General Description
The MAX13037/MAX13038 automotive contact monitor
and level shifters monitor and debounce eight remote
mechanical switches and assert an interrupt (INT) if a
switch changes state. The state of each switch is sam-
pled through an SPI™ interface by reading the status
register. Any switch can be prohibited from asserting an
interrupt by writing to the command register. Four of the
switch inputs are intended for ground-connected
switches (IN0–IN3) and the other four inputs (IN4–IN7)
are programmable in groups of two for either ground-
connected or battery-connected switches. Two switch
inputs (IN0, IN1) have direct level-shifted outputs (DO0,
DO1) to be used for PWM or other timing-based signals.
Switch input thresholds are set to 50% of the voltage
applied to BATREF. The threshold hysteresis is set by
connecting an external resistor from HYST to ground.
The MAX13037/MAX13038 supply an adjustable wet-
ting current to each closed switch to clean mechanical
switch contacts that are exposed to adverse conditions.
The MAX13037/MAX13038 feature a low dropout (LDO)
linear regulator capable of supplying up to 150mA of
current. The MAX13037 LDO has an output voltage of
+5V, whereas the MAX13038 has an output voltage of
+3.3V. The MAX13037/MAX13038 also feature a watch-
dog timer and an open-drain reset output with
adjustable timing.
The MAX13037/MAX13038 operate with a +6V to +26V
battery voltage applied to BAT. The MAX13037/
MAX13038 are available in a 6mm x 6mm, 36-pin TQFN
package and operate over the automotive -40°C to
+125°C temperature range.
Applications
Body Computers
Window Lifters
Seat Movers
Electric Sunroofs
Other Control ECUs
Features
o+6V to +26V Operating Voltage Range
o+42V Compatibility on BAT
oSwitch Inputs Withstand Reverse Battery
o150mA LDO, +5V (MAX13037) or +3.3V
(MAX13038)
oUltra-Low Operating Current 28µA (typ) in 64ms
Scan Mode with LDO ON
oResistor Adjustable Switching Hysteresis
oWatchdog and Reset
oBuilt-In Switch Debouncing
oInterrupt Output
oImmunity to Transients
oHigh Modularity
oThermal Protection
o±8kV HBM ESD Protection on IN0–IN7 Without
External Components
oTwo Inputs (IN0, IN1) Programmable as Direct
Outputs
oFour Inputs (IN4–IN7) Programmable for BAT or
GND Related Switches
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-1084; Rev 0; 11/07
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
+
Denotes a lead-free package.
*
EP = Exposed paddle.
PART
LDO
OUTPUT
VO L T A G E
TEMP
RANGE
PIN-
PACKAGE
PKG
CODE
M A X13 037 ATX+ +5V -40°C to
+125°C
36 TQFN - E P *
( 6m m x
6m m )
T3666-3
M A X13 038 ATX+ +3.3V -40°C to
+125°C
36 TQFN - E P *
( 6m m x
6m m )
T3666-3
Pin Configuration and Typical Application Circuit at end of data sheet.
SPI is a trademark of Motorola, Inc.
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS
(BAT = +6V to +26V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at BAT = +14V, TA= +25°C.) (Note 2)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VLO ........................................................................-0.3V to +6.0V
BAT.........................................................................-0.3V to +42V
IN_ , BATREF...........................................................-45V to +45V
IN_ to BAT ...............................................................-45V to +45V
SD, REGON. ...........................................................-0.3V to +45V
HYST, WET, TD, TDEB, THRESH, OT, INT, RST......-0.3V to 6.0V
CS, CLK, SDI, SDO, WDI,
DO0, DO1, REGOFF.......................................-0.3V to (VLO + 0.3V)
Continuous Current (CS, CLK, SDI, SDO, WDI, DO0,
DO1, REGOFF) .............................................................±20mA
Continuous Power Dissipation (TA= +70°C)
36-Pin TQFN (derate 35.7mW/°C above +70°C) .......2857mW
Junction-to-Case Thermal Resistance (θJC) (Note 1)
36-Pin TQFN .............................................................. 1.4°C/W
Junction-to-Ambient Thermal Resistance (θJA) (Note 1)
36-Pin TQFN ............................................................... 28°C/W
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
POWER SUPPLY
BAT Supply Range V
BAT
626V
BAT Supply Current with
Regulator On I
SUP_REG
V
BAT
= +14V, continuous scan (SC2 = 1,
SC1 = 1, SC0 = 0), programmable
hysteresis off (M0 = M1 = 1),
IN0–IN7 = unconnected, regulator on
(REGON = REGOFF = GND).
57 110 µA
BAT Supply Current with
Regulator Off I
SUP
V
BAT
= +14V, continuous scan (SC2 = 1,
SC1 = 1, SC0 = 0), programmable
hysteresis off (M0 = M1 = 1),
IN0–IN7 = unconnected, regulator off
(REGON = BAT, REGOFF = GND).
46 80 µA
BAT Supply Current in Scan
Mode with Regulator On I
SCAN_REG
V
BAT
= +14V, scan mode (SC0 = 0,
SC1 = 0, SC2 = 0), regulator on
(REGON = REGOFF = GND).
28 48 µA
BAT Supply Current in Scan
Mode with Regulator Off I
SCAN
V
BAT
= +14V, scan mode (SC0 = 0,
SC1 = 0, SC2 = 0), regulator off
(REGON = BAT, REGOFF = GND).
17 35 µA
T
A
= +25°C 3 5
BAT Supply Current in Shutdown
Mode I
SHDN
V
SD
= 0V, V
BAT
= +14V,
REGON = BAT T
A
= +125°C 4 7 µA
BATREF Input Resistance R
BATREF
V
BATREF
= +14V 1 2.7 MΩ
BATREF Input Leakage Current in
Shutdown I
L_BATREF
V
SD
= 0V, V
BATREF
= +14V 1 µA
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a 4-layer
board. For detailed information on package thermal considerations see
www.maxim-ic.com/thermal-tutorial
.
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
_______________________________________________________________________________________ 3
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SWITCH INPUTS (IN0–IN7)
R
HYST
= ∞ or programmable hysteresis
disabled
0.425 x
V
BATRE F
0.5 x
V
BATREF
0.575 x
V
BATRE F
Input Voltage Threshold Center
(Note 3) V
TH_C
R
HYST
= 90kΩ0.4 x
V
BATRE F
0.5 x
V
BATREF
0.63 x
V
BATRE F
V
R
HYST
= ∞ or programmable hysteresis
disabled
0.133 x
V
BATRE F
0.166 x
V
BATREF
0.22 x
V
BATRE F
R
HYST
= 90kΩ0. 26 x
V
BATRE F
0.361 x
V
BATREF
0. 48 x
V
BATRE F
Input Voltage Threshold
Hysteresis (Note 4) V
TH_HYS
R
HYST
= 0Ω0.5 x
V
BATREF
V
Switch-State Sense Resistor R
SENSE
11 16 22 kΩ
Rise 6
Wetting Current Rise/Fall Time
(Note 5)
I
WET_RISE_
FALL
R
WET
= 61kΩFall 1 µs
R
WET
= 61kΩ22
R
WET
= 30kΩ28 40 51Wetting Current I
WET
R
WET
= 330kΩ7.5
mA
IN0–IN7 Input Impedance in
Shutdown V
SD
= 0V, V
IN
_ = +14V 5.5 8.5 MΩ
ESD Protection IN0–IN7 Human Body Model (HBM) 8 kV
LOGIC-LEVELS (CS, CLK, SDI , SDI, DO0, DO1, INT, OT, RST, SD, REGON, REGOFF)
SDO, DO1, DO2
Output Voltage High V
OH
Source current = 2mA 0.8 x V
LO
V
SDO, DO1, DO2
Output Voltage Low V
OL
Sink current = 4mA 0.2 x V
LO
V
INT, OT, RST Output Voltage Low V
INTL
Sink current = 4mA 0.4 V
SD Input Leakage Current I
L_SD
V
SD
= V
BAT
= +14V 1 µA
SD, REGON Input Voltage Low V
IL_SD
0.8 V
SD, REGON Input Voltage High V
IH_SD
2.4 V
REGON Pullup Current I
REGON
REGON = 0 0.4 1 3.0 µA
CS, CLK, SDI, REGOFF, WDI
Input Voltage Low V
IL
0.33 x V
LO
V
CS, CLK, SDI, REGOFF, WDI
Input Voltage High V
IH
0.66 x V
LO
V
CS, CLK, WDI, REGOFF Input
Leakage Current I
IL
-1 +1 µA
INT, OT, RST Leakage Current I
OL
-1 +1 µA
SDI Pulldown Resistor R
SDI
65 100 145 kΩ
ELECTRICAL CHARACTERISTICS (continued)
(BAT = +6V to +26V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at BAT = +14V, TA= +25°C.) (Note 2)
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(BAT = +6V to +26V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at BAT = +14V, TA= +25°C.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
LINEAR REGULATOR
MAX13037, VBAT = +14V, ILOAD = 1mA 4.92 5.00 5.08
Output Voltage VLO MAX13038, VBAT = +14V, ILOAD = 1mA 3.234 3.300 3.366 V
VLO = +5V
(MAX13037) 0.53 1
ILOAD = 1mA to 50mA,
VBAT = +14V VLO = +3.3V
(MAX13038) 0.53 1
VLO = +5V
(MAX13037) 1 1.85
Load Regulation LOAD _REG
ILOAD = 1mA to 150mA,
VBAT = +14V VLO = +3.3V
(MAX13038) 1 1.85
%
Line Regulation LINE_REG VBAT = +6V to +26V -0.9 +0.9 mV/V
VLO = +5V, ILO = 50mA (MAX13037) 330
VLO = +5V, ILO = 150mA (MAX13037) 1000Dropout Voltage VDROP
VLO = +3.3V, ILO = 150mA (MAX13038) 1300
mV
Output Current Limit ILIM VBAT = +14V 150 mA
Power-Supply Rejection Ratio PSRR ILO = 10mA, f = 100Hz, 500mVP-P,
AC-coupled into VBAT 68 dB
Start-Up Time tSTART 1ms
RESET, WATCHDOG
Reset Reference Voltage VRST THRESH from high to low 1.20 1.24 1.28 V
THERMAL SHUTDOWN
Thermal Shutdown Temperature TSHDN (Note 6) 165 °C
Thermal Shutdown Temperature
for Wetting Currents Only TWARN (Note 7) 135 °C
Thermal Shutdown Hysteresis THYST 15 °C
TIMING CHARACTERISTICS
(BAT = +6V to +26V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at BAT = +14V, TA= +25°C.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
V
BAT
= +6V 22 35
IN0 to DO0 Propagation Delay,
IN1 to DO1 Propagation Delay t
PROP
V
BAT
= +14V 22 µs
CLK Frequency f
CLK
Input rise/fall time < 2ns 5 MHz
Falling Edge of CS to Rising
Edge of CLK
Required Setup Time
t
LEAD
Input rise/fall time < 2ns, Figure 1 110 ns
Falling Edge of CLK to Rising
Edge of CS
Required Setup Time
t
LAG
Input rise/fall time < 2ns, Figure 1 50 ns
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
_______________________________________________________________________________________ 5
TIMING CHARACTERISTICS (continued)
(BAT = +6V to +26V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at BAT = +14V, TA= +25°C.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SDI to Falling Edge of CLK
Required Setup Time t
SI(SU)
Input rise/fall time < 2ns, Figure 1 30 ns
Falling Edge of CLK to SDI
Required Hold Time t
SI
(
HOLD
)
Input rise/fall time < 2ns, Figure 1 20 ns
Time from Falling Edge of CS to
SDO Low Impedance t
SO(EN)
Input rise/fall time < 2ns, Figure 1 55 ns
Time from Rising Edge of CS to
SDO High Impedance t
SO
(
DIS
)
Figures 1 and 2 55 ns
Time from Rising Edge of CLK to
SDO Data Valid t
VALID
C
SDO
=15pF, Figure 1 70 ms
C
TDEB
= 500pF 3.18 5.9 9.42 ms
Debounce Time t
DEB
C
TDEB
= 10nF 63 120 188 ms
Scanning Time Pulse t
SCAN
130 250 400 µs
Scanning Time Period t
SCAN-P
SC0 = 0, SC1 = 1, SC2 = 1 4 8 14 ms
Wetting Time Pulse t
WETT
WTOFF = 0 10 21 35 ms
Time from Shutdown to Normal
Operation t
SD
SD low-to-high transition to input monitoring
enabled 200 µs
Time from SCAN Mode to Normal
Operation t
SM
(Note 8) 500 µs
Reset Output Pulse Width t
RST
C
TD
= 10nF (Figure 3) 10 21 36 ms
Watchdog Timeout Period 1 t
WD1
C
TD
= 10nF, time before INT goes low
(Figure 3) 40 84 144 ms
Watchdog Timeout Period 2 t
WD2
C
TD
= 10nF, time before RST goes low
(Figure 3) 2 x t
WD1
ms
Minimum Watchdog Timeout
Reset on WDI t
WDI
300 ns
Note 2: All units are 100% production tested at TA= 125°C. Limits over the operating temperature range are guaranteed by design and
not production tested.
Note 3: VTH_C = (VTH_HIGH + VTH_LOW) / 2.
Note 4: VTH_HYS = (VTH_HIGH - VTH_LOW).
Note 5: Wetting current rise/fall time is measured as the time it takes to go from 20% to 80% of the maximum wetting current.
Note 6: TSHDN is the temperature at which the wetting currents and LDO are disabled.
Note 7: TWARN is the temperature at which only the wetting currents are disabled.
Note 8: When exiting SCAN mode to enter Normal Mode (through SPI) any input change is ignored for 500µs (typ) to allow correct
wake-up of input comparators. After this time elapses, the inputs are monitored in continuous mode.
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
6 _______________________________________________________________________________________
CS
CLK
SDI MSB IN
MSB OUT LSB OUT
tSO(DIS)
tVALID
tSO(EN)
tLEAD
SDO
tLAG
tSI(SU) tSI(HOLD)
Figure 1. SPI Timing Characteristics
MAX13037/
MAX13038
CS
SDO
SDOCS
15pF 1/3VL
1kΩ
tSO(EN)
VL
tSO(DIS)
VOL + 0.1VL
Figure 2. SDO Enable/Disable Test Circuit and Timing Diagram
WDI
INT
RST
NORMAL OPERATION
(NO SWITCHES ACTIVE)
tWD1
tWD1
tWD2 tRST
Figure 3. Watchdog Interrupt/Reset Timing Diagram
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
_______________________________________________________________________________________
7
WETTING CURRENT vs. VBAT
MAX13037/8toc01
VBAT (V)
WETTING CURRENT (mA)
1410 18 22
-20
-10
0
10
20
30
-30
626
GND-CONNECTED SWITCH
BAT-CONNECTED SWITCH
WETTING CURRENT vs. RWET
MAX13037/8toc02
RWET (kΩ)
WETTING CURRENT (mA)
280180 23013080
-50
0
-30
-20
10
-40
20
40
-10
50
30
30 330
GND-CONNECTED SWITCH
BAT-CONNECTED SWITCH
WETTING CURRENT PULSE (NORMAL MODE
,
WTOFF = 0, WEN = WEND = 1)
MAX13037/8toc03
VIN_
10V/div
IIN_
20mA/div
INT
2V/div
20ms/div
BAT CURRENT vs. TEMPERATURE
(NORMAL MODE)
MAX13037/8toc04
TEMPERATURE (°C)
IBAT (μA)
0
100
70
40
80
50
20
10
90
60
30
110
-40 125-10-25 5 3520 50 8065 95 110
ADJUSTABLE HYSTERESIS ON
ADJUSTABLE HYSTERESIS OFF
BAT CURRENT vs. TEMPERATURE
(NORMAL MODE)
MAX13037/8toc05
TEMPERATURE (°C)
IBAT (μA)
0
7
2
5
6
3
1
4
8
-40 125-25 95 11020-10 5 35 8050 65
SD = LOW
BAT CURRENT vs. TEMPERATURE
(SCANNING MODE)
MAX13037/8toc06
TEMPERATURE (°C)
IBAT (μA)
20
40
25
45
35
30
-40 12595 1105035205-10-25 8065
LDO = ON
SCANNING PERIOD = 2ms
SCANNING PERIOD = 64ms
TYPICAL IN0 DRIVING
(NORMAL MODE, WTOFF = WEN = WEND = 0)
MAX13037/8toc07
40μs/div
VIN0
5V/div
VDO0
2V/div
f = 5kHz
TYPICAL IN0 DRIVING
(NORMAL MODE, WTOFF = WEN = WEND = 0)
MAX13037/8 toc08
2ms/div
VIN0
5V/div
VDO0
2V/div
f = 100Hz
ADJUSTABLE HYSTERESIS OFF
HYSTERESIS vs. RHYST
MAX13037/8toc09
RHYST (kΩ)
HYSTERESIS (V)
0
7
2
5
6
3
1
4
8
0 400 1000200 600 800
ADJUSTABLE HYSTERESIS ON
Typical Operating Characteristics
(BAT = +14V, SD = VBAT, RWET = 61kΩ, RHYST = 90kΩ, CTDEB = 4700pF, CTD = 4700pF, TA= +25°C, unless otherwise noted.)
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(BAT = +14V, SD = VBAT, RWET = 61kΩ, RHYST = 90kΩ, CTDEB = 4700pF, CTD = 4700pF, TA= +25°C, unless otherwise noted.)
SWITCHING THRESHOLD vs. TEMPERATURE
MAX13037/8toc10
TEMPERATURE (°C)
SWITCHING THRESHOLD (V)
5
8
6
9
7
10
-40 95 12511053520-10-25 806550
ADJUSTABLE HYSTERESIS OFF
VIN_ RISING
VIN_ FALLING
SWITCHING THRESHOLD vs. VBAT
MAX13037/8toc11
VBAT (V)
SWITCHING THRESHOLD (V)
0
20
10
5
15
62618 2210 14
ADJUSTABLE HYSTERESIS OFF
VIN_ RISING
VIN_ FALLING
INPUT WAVEFORM IN SCAN MODE
(SCAN MODE, WTOFF = WEN = 0, WEND = 1)
MAX13037/8toc12
400μs/div
VIN_
5V/div
SCANNING PERIOD = 2ms
INPUT SWITCH OPEN
DEBOUNCE TIME vs. TEMPERATURE
MAX13037/8toc13
TEMPERATURE (°C)
DEBOUNCE TIME (ms)
40
44
58
42
54
52
56
48
46
50
60
-40 125-10-25 1109535205806550
DEBOUNCE TIME vs. BAT VOLTAGE
MAX13037/8toc14
VBAT (V)
DEBOUNCE TIME (ms)
47
50
48
51
49
6261410 2218
DEBOUNCE TIME vs. CTDEB
MAX13037/8toc15
CTDEB (pF)
DEBOUNCE TIME (ms)
0
40
100
120
20
80
60
0 10,00040002000 80006000
VLO OUTPUT VOLTAGE vs. TEMPERATURE
MAX13037/8toc16
TEMPERATURE (°C)
VLO OUTPUT VOLTAGE (V)
3.0
5.0
3.5
5.5
4.5
4.0
-40 12595 1105035205-10-25 8065
VLO OUTPUT VOLTAGE vs. LOAD CURRENT
MAX13037/8toc17
LOAD CURRENT (mA)
VLO OUTPUT VOLTAGE (V)
50 100 150
2.0
4.5
5.0
2.5
3.0
3.5
4.0
5.5
0200
MAX13038
MAX13037
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
_______________________________________________________________________________________ 9
Pin Description
PIN NAME FUNCTION
1, 15, 31 GND Ground
2 IN0 Switch Input Channel 0. Connect IN0 to a switch connected to GND. IN0 can be programmed as a
direct input with a level-shifted output on DO0 (see the Mechanical Switch Inputs (IN0–IN7) section).
3 IN1 Switch Input Channel 1. Connect IN1 to a switch connected to GND. IN1 can be programmed as a
direct input with a level-shifted output on DO1 (see the Mechanical Switch Inputs (IN0–IN7) section).
4 IN2 Switch Input Channel 2. Connect IN2 to a switch connected to GND.
5 IN3 Switch Input Channel 3. Connect IN3 to a switch connected to GND.
6 IN4 Switch Input Channel 4. Connect IN4 to a switch connected to GND or BAT.
7 IN5 Switch Input Channel 5. Connect IN5 to a switch connected to GND or BAT.
8 IN6 Switch Input Channel 6. Connect IN6 to a switch connected to GND or BAT.
9 IN7 Switch Input Channel 7. Connect IN7 to a switch connected to GND or BAT.
10, 11, 34 N.C. No Connection. Not internally connected.
12 HYST Hysteresis Input. Connect HYST to GND with a 0Ω to 900kΩ resistor to set the input voltage
hysteresis on IN0–IN7.
13 WET Wetting Current Input. Connect a 30kΩ to 330kΩ resistor from WET to GND to set the wetting current
on IN0–IN7.
14 TDEB Switch Debounce Time Input. Connect a 500pF to 10nF capacitor from TDEB to GND to set the
switch debounce time.
16 OT Overtemperature Warning Output. OT is an open-drain output that asserts low when the thermal
warning threshold is exceeded.
17 INT Interrupt Output. INT is an open-drain output that asserts low when one or more of the IN0–IN7 inputs
change state and are enabled for interrupts or when the watchdog times out.
18 TD Reset and Watchdog Timeout Input. Connect TD to GND with a 500pF to 10nF capacitor to set the
timeout period for the reset and watchdog.
VLO TRANSIENT LOAD REGULATION
MAX13037/8toc18
1ms/div
ILO
50mA/div
VLO
(AC-COUPLED)
50mV/div
Typical Operating Characteristics (continued)
(BAT = +14V, SD = VBAT, RWET = 61kΩ, RHYST = 90kΩ, CTDEB = 4700pF, CTD = 4700pF, TA= +25°C, unless otherwise noted.)
WATCHDOG INTERRUPT AND RESET
PERIOD vs. TEMPERATURE
MAX13037/8toc19
TEMPERATURE (°C)
PERIOD (ms)
50
90
70
80
60
100
-40 125-10-25 5 20 35 65 11050 80 95
WATCHDOG INTERRUPT AND RESET
PERIOD vs. CTD
MAX13037/8toc20
CTD (pF)
PERIOD (ms)
0
100
125
50
75
25
150
0 10,0002000 80004000 6000
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
10 ______________________________________________________________________________________
Pin Description (continued)
PIN NAME FUNCTION
19 SD Shutdown Input. Drive SD low to place the MAX13037/MAX13038 into shutdown mode and disable
the linear regulator. Drive SD high for normal operation. SD is compatible with voltages up to VBAT.
20 REGON
Linear Regulator Enable Input (Active Low). Connect REGON to INT to enable a wake-up when a
switch status change is detected. Drive REGON using an open-drain logic output to control the
regulator directly. REGON is internally pulled up to an internal bias voltage of approximately +4.8V.
21 REGOFF Linear Regulator Disable Input (Active Low). REGOFF is used in conjunction with REGON when the
internal regulator is enabled by an interrupt (see the Low-Dropout Linear Regulator (VLO) section).
22 CS SPI Chip-Select Input. Drive CS low to enable the clocking of data into and out of the
MAX13037/MAX13038. SPI data is latched into the MAX13037/MAX13038 on the rising edge of CS.
23 SDO SPI Serial-Data Output. SPI data is output on SDO on the rising edges of CLK while CS is held low.
SDO is three-state when CS is high.
24 SDI SPI Serial-Data Input. SPI data is latched into the internal shift register on the falling edges of CLK
while CS is held low. SDI has an internal 100kΩ pulldown resistor.
25 CLK SPI Serial-Clock Input
26 RST Reset Output. RST is an open-drain output that asserts low when VLO is below the threshold
determined by the THRESH input. RST also asserts low when the watchdog times out.
27 DO1 Data Output Channel 1. DO1 is the level-shifted output of IN1 when WEND = 0.
28 DO0 Data Output Channel 0. DO0 is the level-shifted output of IN0 when WEND = 0.
29 THRESH Reset Threshold Level Input. Connect THRESH to a resistor divider between VLO and GND to set the
reset reference level.
30 WDI Watchdog Timer Input. The watchdog timer is reset at every transition on the WDI input.
32 BATREF Battery Reference Input. Switch thresholds are set to 50% of the voltage applied to BATREF. Connect
BATREF to the system’s battery supply voltage.
33 VLO
Linear Regulator Output. VLO is the output of an internal linear regulator and is the reference voltage
for all digital I/O. Bypass VLO with a 2.2µF or greater ceramic capacitor. Alternatively, a 10µF
electrolytic capacitor can be used in parallel with a 0.1µF ceramic capacitor.
35, 36 BAT
Battery Supply Input. Connect BAT to a positive +6V to +26V battery supply voltage. Bypass BAT to
ground with a 0.1µF ceramic capacitor and a 10µF electrolytic capacitor placed as close as possible
to BAT.
— EP Exposed Paddle. Connect EP to GND.
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
______________________________________________________________________________________ 11
Detailed Description
The MAX13037/MAX13038 automotive contact monitor
and level shifters monitor and debounce eight remote
mechanical switches and assert an interrupt (INT) if a
switch changes state. Any of the switch inputs can be
prohibited from asserting an interrupt. The switch
threshold levels are set to 50% of the voltage applied to
BATREF and all switch inputs feature a common
adjustable hysteresis, debounce time, and wetting cur-
rent. Two switch inputs (IN0, IN1) are programmable to
have direct outputs (DO0, DO1), useable for PWM or
other timing-based signals.
The MAX13037/MAX13038 feature an SPI interface to
monitor individual switch inputs and to configure inter-
rupt masking, hysteresis, and wetting current
enable/disable, switch configuration (battery-
connected or ground-connected), and scanning period.
The MAX13037/MAX13038 provide an internal low
dropout (LDO) linear regulator capable of supplying up
to 150mA. The LDO can be enabled or disabled
through two digital control inputs: REGON and REGOFF.
A watchdog timer and power-on reset circuitry is provid-
ed on the MAX13037/MAX13038 to supervise external
microcontrollers (µC).
The MAX13037/MAX13038 feature three modes of
operation: normal mode, scanning mode, and shut-
down mode. In normal mode, the part is fully functional
and internal sensing resistors are connected to all
switch inputs. In scanning mode, the sensing resistors
are connected for a finite duration to reduce power
consumption. In shutdown mode, all switch inputs are
high impedance and the internal LDO is switched off to
further reduce power consumption.
Functional Diagram
MAX13037
MAX13038
WAKE-UP
LOGIC
LINEAR
REGULATOR
WETTING
CURRENT
CONTROL
LEVEL
TRANSLATORS SHIFT
REGISTER
SPI
INTERFACE
INTERRUPT
LOGIC
IN0
IN1
IN2
IN3
IN4
IN5
IN6
DIGITAL
INTERFACE
RESET +
WATCHDOG
IN7
REGON
REGOFF
BATREF
OT
RST
INT
SDO
CS
SDI
CLK
WDI
TD
THRESH
DO0
VLO
DO1
SD BAT
WET TDEB GNDHYST
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
12 ______________________________________________________________________________________
BAT
BAT is the main power-supply input. Bypass BAT to
ground with a 0.1µF ceramic capacitor placed as close
as possible to BAT. In addition, bypass BAT with a
10µF or greater capacitor. BAT can withstand DC volt-
ages up to +42V.
Low-Dropout Linear Regulator (VLO)
The MAX13037/MAX13038 contain an internal LDO lin-
ear regulator supplied by the BAT input. The LDO out-
put voltage is present on VLO and is capable of
supplying up to 150mA of current. The MAX13037 out-
put voltage is set to +5V and the MAX13038 output
voltage is set to +3.3V.
The LDO regulator is controlled through the REGON
and REGOFF inputs as shown in Figure 4. REGON is
an input able to withstand voltages up to VBAT. The
LDO startup time is 1ms (typ).
There are two options for controlling the linear regulator:
•Wake-Up on Interrupt: In this case, REGON is con-
nected to INT and when the MAX13037/MAX13038
generate an interrupt, the linear regulator is turned
on, thus providing power to the local µCs. The µC
pulls REGOFF high to keep the regulator on before
making an SPI read (which causes INT and REGON
to go high). The linear regulator can then be turned
off by pulling REGOFF low.
•Direct Control: In this case, the regulator is
enabled/disabled by some other signal in the sys-
tem which must be connected to REGON. If
REGOFF is not used, it must be connected to GND
to allow the turnoff of the LDO.
Linear Regulator Wake-Up
Regulator wake-up can be controlled with the INT out-
put by connecting it to REGON. REGON is a TTL input
with an internal pullup to a low-voltage internal refer-
ence of +4.8V (typ). With this control scheme, any
change of the input switches (enabled for interrupt gen-
eration) causes the regulator to turn on, thus providing
power to any external circuitry connected to VLO. If an
external microcontroller is supplied from VLO, the
microcontroller can keep the LDO on by forcing
REGOFF high. Reading from the MAX13037/MAX13038
over the SPI interface causes the INT output to go into
high-impedance so that both INT and REGON are
pulled high. After this phase, the microcontroller can
turn off the regulator again by driving REGOFF low.
Note that it is also possible to tie multiple open-drain
active-low outputs in an ORing configuration, allowing
the wakeup of the regulator from other devices.
If the INT output is not used to control the regulator,
connect the REGOFF input to ground and use REGON
to enable or disable the regulator as shown in Figure 4.
Watchdog Timer (WDI)
The MAX13037/MAX13038 feature a watchdog timer
that is reset on every transition on the WDI input. If
there is no transition on WDI before the first timeout
period (tWD1) the INT output asserts low. If there is still
no transition on WDI after the second timeout period
(tWD2), the RST output is pulsed low for tRST and the
INT output deasserts (see Figure 3). The watchdog
timeout period can be adjusted by changing the
capacitor value on the TD input.
tRST (ms) = 2 x CTD (nF)
tWD1 = 4 x tRST (ms)
tWD2 = 8 x tRST (ms)
Note that WDI can be tied to the CS input to allow a
watchdog reset for every read/write operation over the
SPI interface. To avoid any corruption of the internal
command register, it is necessary to transmit the full pro-
gramming word (16 bits) for every CS negative pulse.
Reset Output (
RST
)
The RST output asserts low when a watchdog timeout
occurs or when the LDO output voltage drops below a
certain threshold. The threshold voltage is set by con-
necting an external voltage divider on the THRESH
input between VLO and GND. The voltage on THRESH
is compared with an internal reference voltage of
+1.24V and if it is lower, the RST output asserts low
for tRST and remains low if VLO does not rise above
the threshold.
REGOFF = 1
REGOFF = 0
REGOFF = 0
LDO ON
REGON = 0
REGOFF = 0
LDO ON
REGON = 0
REGOFF = 1
LDO ON
REGON = 1
REGOFF = 1
LDO OFF
REGON = 1
REGOFF = 0
REGON = 1 REGON = 0 REGON = 0 REGON = 1
REGOFF = 1 IS NOT ALLOWED
BECAUSE VLO IS ABSENT.
Figure 4. Linear Regulator State Diagram
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
______________________________________________________________________________________ 13
Mechanical Switch Inputs (IN0–IN7)
IN0–IN7 are the inputs for remote mechanical switches.
The status of each switch input is indicated by the SW0
through SW7 bits in the status register, and each switch
input can be programmed to not assert an interrupt
(INT) by writing to the P0–P7 bits in the command reg-
ister. All switch inputs are configured to assert an inter-
rupt upon power-up.
The first four inputs (IN0–IN3) are intended for ground-
connected switches. The remaining four inputs (IN4–IN7)
can be programmed in sets of two for either ground-con-
nected or battery-connected switches by writing to the
M0 and M1 bits (see Table 5). The default state after
power-up is IN2–IN7 configured for ground-connected
switches, and IN0/IN1 configured for direct inputs.
All switch inputs have internal 16kΩsense resistors to
detect switch transitions. Inputs configured for ground-
connected switches are pulled up to BAT and inputs con-
figured for battery-connected switches are pulled down to
GND. Figure 5 shows the switch input structure for IN0
and IN1. IN0 and IN1 can be programmed as direct
inputs with level-shifted outputs (DO0 and DO1) by clear-
ing the WEND bit in the command register (normal mode
only). When programmed as direct inputs, IN0 and IN1
can be used for PWM or other signaling. Clearing the
WEND bit disables the sense resistors and wetting cur-
rents on IN0 and IN1. When programmed as direct inputs,
the status of IN0 and IN1 is not reflected in the status reg-
ister, and interrupts are not allowed on these inputs.
Switch Threshold Levels and
Hysteresis (BATREF, HYST)
Input thresholds for the remote switches are 50% of the
voltage applied to BATREF. The BATREF input is typical-
ly connected to the battery voltage before the reverse-
battery protection diode. The MAX13037/MAX13038
feature adjustable hysteresis on the switch inputs by
connecting an external 0 to 900kΩresistor from HYST to
ground (normal mode only). Short HYST to ground to
obtain the maximum hysteresis of (0.5 x VBATREF). The
approximate formula for hysteresis is given below:
To reduce power consumption, the adjustable hystere-
sis can be disabled by setting [SC2:SC1:SC0 = 1:1:0]
in the command register. When the adjustable hystere-
sis is disabled, the hysteresis is set to 0.166 x VBATREF.
Switch Debounce and Deglitch
The switch inputs IN0–IN7 share a common program-
mable debounce timer to increase the noise immunity
of the system in normal and scan mode. The switch
debounce time is set by connecting a capacitor
between the tDEB input and ground. The minimum
value of this capacitor is 500pF and the maximum value
is 10nF, corresponding to a debounce time of 5ms to
100ms respectively. To calculate other debounce times
the following formula should be used:
C(nF) = tDEB(ms) / 10
All switch input glitches of less than 20µs in duration are
automatically rejected by the MAX13037/MAX13038.
Debounce in Normal Mode
When a change of state occurs at the switch input the
debounce timer starts. If the new state is stable for at least
tDEB, the status register is updated and an interrupt is
generated (if enabled). If the input returns to its previous
state before the debounce time has elapsed, an interrupt
is not generated and the status register is not updated.
Debounce in Scan Mode
A change of state at the switch input causes the device to
automatically enter normal mode and the debounce timing
to start. The device remains in normal mode as long as the
input state differs from the previous state. As soon as the
debounce time ends, the status register is updated, an
interrupt is generated, and the device re-enters scan mode.
If the input returns to its previous state before the end
of the debounce time, the device re-enters scan mode,
an interrupt is not generated, and the status register is
not updated.
VRV
HYST HYST(k ) BATREF
=+
+
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
Ω
0 166 43
123
.(( )
()
MAX13037
MAX13038
16kΩ*
NOTES:
*WETTING CURRENT AND PULLUP/DOWN RESISTORS ARE
CONTROLLED BY THE WEN AND WEND BITS IN THE COMMAND
REGISTER (SEE TABLE 4).
WETTING*
CURRENT
IN0, IN1
VBAT
CONTROL
LOGIC
Figure 5. Input Structure of IN0 and IN1
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
14 ______________________________________________________________________________________
Wetting Current (WET)
The MAX13037/MAX13038 feature adjustable wetting
current to any closed switch to clean switch contacts
that are exposed to adverse conditions. The wetting
current is set by connecting a 30kΩto 330kΩresistor
from WET to ground. A 30kΩresistor corresponds to a
wetting current of 40mA (typ) and a 330kΩresistor cor-
responds to a 4mA (typ) wetting current. See the
Typical Operating Characteristics
section for the rela-
tionship between the wetting current and RWET.
The WEN and WEND bits in the command register
enable and disable the wetting currents and the
WTOFF bit allows the wetting current to be activated for
a duration of 20ms (typ) (see the
Command Register
section). Disabling wetting currents, or limiting the
active wetting current time reduces power consump-
tion. The default state upon power-up is all wetting cur-
rents disabled.
Wetting current is activated on closed switches just
after the debounce time. The wetting current pulse
starts after the debounce time. A wetting current pulse
is provided to all closed switches when a valid input
change is detected. Wetting current rise and fall times
are controlled to enhance EMC performance. There is
one wetting current timer for all switch inputs.
Therefore, it is possible to observe wetting pulses
longer than expected whenever two switches turn on in
sequence and are spaced out less than tWET. In scan
mode, the wetting current is enabled during the polling
pulse only.
When using wetting currents, special care must be
taken to avoid exceeding the maximum power dissipa-
tion of the MAX13037/MAX13038 (see the
Applications
Information
section).
Switch Outputs (DO0, DO1)
DO0 and DO1 are direct level-shifted outputs of the
switch inputs IN0 and IN1 when the WEND bit of the
command register is cleared and when operating in
normal mode. When configured as direct inputs, the
wetting currents and sensing resistors are disabled on
IN0 and IN1. DO0 and DO1 are three-stated when the
WEND bit is set or when operating in scan mode.
When programmed as direct inputs, the status of IN0
and IN1 are not reflected in the status register and
interrupts are not allowed on these inputs.
Interrupt Output (
INT
)
INT is an active-low, open-drain output that asserts
when any of the switch inputs change state, as long as
the particular input is enabled for interrupts (set by
clearing P7–P0 in the command register). INT also
asserts when the first watchdog timeout period elapses
(tWD1). A pullup resistor to VLO is needed on INT. INT is
cleared when CS is driven low for a read/write operation.
The INT output still asserts when VLO is disabled pro-
vided that it is pulled up to a different supply voltage.
Thermal Protection (
OT
)
The MAX13037/MAX13038 feature a two-level thermal
protection strategy that prevents the device from being
damaged by overheating. At the initial warning temper-
ature of +135°C (typ), only wetting currents are dis-
abled. The MAX13037/MAX13038 return to normal
operation after the internal temperature decreases
below +120°C (typ). This protection feature is disabled
when WEN = 0 or when all inputs are open. At the sec-
ond thermal warning temperature of +170°C (typ), the
LDO is shut down. Because a µC is often supplied by
the LDO, an overheating event caused by excessive
power dissipation related to I/O wetting currents is nor-
mally resolved without affecting the µC status.
An open-drain, active-low output (OT) asserts low when
the internal temperature of the device rises above the
thermal warning threshold. OT is immediately cleared
when the CS input is driven low for read/write opera-
tions, regardless of whether the temperature is above
the threshold, or not. The overtemperature status of the
MAX13037/MAX13038 can also be monitored by read-
ing the OT bit in the status register. The OT bit is set
when the internal temperature rises above the tempera-
ture threshold, and it is cleared when the temperature
falls below the temperature hysteresis level. This allows
a µC to monitor the overtemperature status, even if the
OT output has been cleared. See Figure 6 for an exam-
ple timing diagram of the overtemperature alerts.
If desired, the OT and INT outputs can be connected
to the same µC GPIO in a wired-OR configuration to
save a µC pin. The OT output still asserts when VLis
absent provided that it is pulled up to a different sup-
ply voltage.
TEMPERATURE
OT
CS
OT BIT
Figure 6. Example Timing Diagram of the Overtemperature Alerts
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
______________________________________________________________________________________ 15
Serial Peripheral Interface
(
CS
, SD0, SDI, CLK)
The MAX13037/MAX13038 operate as a Serial Peripheral
Interface (SPI) slave devices. An SPI master accesses
the MAX13037/MAX13038 by reading from a status reg-
ister and writing to a command register. Both registers
are 16 bits long and are accessed most significant bit
(MSB) first.
On the falling edge of CS, the status register is immedi-
ately loaded to an internal shift register and the con-
tents are transferred out of the SDO output on the rising
edge of CLK. Serial data on the SDI input is latched
into the shift register on the falling edge of CLK. On the
rising edge of CS, the contents of the shift register are
copied to the command register (see Figure 7). The
status and command registers are 16 bits wide, so it is
essential to clock a total of 16 bits while CS is low for
the input and output data to be valid. When CS is high,
the SDO output is high-impedance and any transitions
on CLK and SDI are ignored. The INT and OT flags are
cleared on the CS falling edge. Input status changes
occurring during the CS reading/writing operation are
allowed. If a switch status changes when CS is low, the
interrupt is asserted as usual. This allows the part to be
used even if VLO is disabled provided that the INT out-
put is pulled up to another supply voltage.
Status Register
The status register contains the status of the switches
connected to IN7 through IN0 and it also contains an
overtemperature warning bit (see Table 1). The status
register is accessed through an SPI-compatible master.
Notes:
Bits 15–8: Switch 7 Through 0 Status (SW7–SW0)
SW7 through SW0 reflect the status of the switches
connected to inputs IN7 through IN0, respectively.
Open switches are returned as a [0] and closed switch-
es are returned as a [1].
Bit 7: Overtemperature Warning (OT)
The OT bit returns a [1] when the internal temperature of
the MAX13037/MAX13038 is above the temperature
warning threshold of +135°C (typ). The OT bit returns a
[0] when the MAX13037/MAX13038 is either below the
temperature threshold, or it has fallen below the tempera-
ture hysteresis level following an overtemperature event.
Bits 6–0: Unused
Bits 6 through 0 are unused and should be ignored.
Command Register
The command register is used to configure the
MAX13037/MAX13038 for various modes of operation
and is accessed by an SPI-compatible master (see
Table 2). The power-on reset (POR) value of the com-
mand register is 0x00.
CLK
* = UNUSED.
SDI
CS
SDO
15
STATUS REGISTER
IS COPIED TO
SHIFT REGISTER
SHIFT REGISTER IS
COPIED TO COMMAND
REGISTER
14131211109876543210
WTOFF SC2 SC1 SC0 WEN WEND M1 M0 P7 P6 P5 P4 P3 P2 P1 P0
SW7 SW6 SW5 SW4 SW3 SW2 SW1 SW0 OT * * * * * * *
Figure 7. SPI Read/Write Example
Table 1. Status Register
BIT 151413121110 9 8 7 6 5 4 3 2 1 0
NAME SW7 SW6 SW5 SW4 SW3 SW2 SW1 SW0 OT — — — — — — —
Table 2. Command Register
BIT 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
NAME WTOFF SC2 SC1 SC0 WEN WEND M1 M0 P7 P6 P5 P4 P3 P2 P1 P0
POR 0 0000 0 0000000000
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
16 ______________________________________________________________________________________
Notes:
Bit 15: Wetting Current Mode (WTOFF)
Set the WTOFF bit to configure the wetting currents as
continuous on closed switches. Clear the WTOFF bit to
configure the wetting current as a pulse where the wet-
ting current is turned on for a set duration of 20ms after
a switch closes (and the debounce is timed out). After
20ms elapses, the wetting current is turned off. Either
wetting current mode is only applicable to switches that
have wetting currents enabled (see WEN and WEND
bits). In scan mode, the wetting currents are on for the
polling time of 250µs (typ) and are pulsed at the pro-
grammed scanning period. When WTOFF is set, the
wetting current continuously pulses at the programmed
scanning period. When WTOFF is cleared, the wetting
current pulses at the programmed scanning period, but
turns off after 20ms elapses.
Bits 14, 13, 12: Scanning Period (SC2, SC1, SC0)
The SC2, SC1, and SC0 bits are used to program the
scanning period as depicted in Table 3. Switch inputs
are simultaneously polled for a finite duration of 250µs
(typ), and polling occurs at a period selected through
the SC2, SC1, and SC0 inputs. Figure 8 shows a timing
diagram of switch scanning and sampling. When the
inputs are not being polled, the sense resistors are dis-
connected, reducing the current consumption caused
from polling closed switches. For a continuous scanning
period ([SC2:SC1:SC0] = [1:1:1] or [1:1:0]), the switch
inputs are constantly being monitored and the sense
resistors are always connected. The state [SC2:SC1:SC0]
= [1:1:0] also disables adjustable hysteresis (normally set
by RHYST) and fixes hysteresis at 0.166 x VBATREF. When
adjustable hysteresis is not needed, it is recommended to
disable this feature to reduce power consumption.
Bit 11: Global Wetting Current Enable (WEN)
The WEN bit is a global enable for the wetting currents
on all the channels. Set the WEN bit to enable wetting
currents on all channels and clear the WEN bit to dis-
able wetting currents. Even with wetting currents glob-
ally enabled, the wetting currents and sense resistors
on IN0 and IN1 can still be turned off with the WEND bit
(see Table 4).
Bit 10: IN0 and IN1 Wetting Current Enable (WEND)
The WEND bit is used to turn on wetting currents and
sense resistors on inputs IN0 and IN1. Set the WEND
bit to enable wetting currents on IN0 and IN1 and clear
the WEND bit to turn off the wetting current and sense
resistors on IN0 and IN1. When the wetting currents
and sense resistors are disabled (WEND = 0), IN0 and
IN1 are configured as direct inputs with level-shifted
outputs on DO0 and D01. DO0 and DO1 can only be
used as level-shifted outputs in normal mode and are
three-stated in scan mode (see the
Scan Mode
sec-
tion). Note that both the WEN and WEND bits need to
be set for wetting currents to be enabled on IN0 and
Table 3. Programmable Scanning Period
SC2 SC1 SC0 SCANNING PERIOD (ms)
000 64
001 32
010 16
011 8
100 4
101 2
110
Continuous/adjustable
hysteresis off
1 1 1 Continuous
GND-CONNECTED
SWITCH INPUT
SWITCHES ARE
POLLED FOR 250μsSWITCH
DEBOUNCE
STARTS
INT
tSCAN
tSCAN-P tDEB
SWITCH
CLOSES
STATUS REGISTERS AND
INT ARE UPDATED
AFTER tDEB
Figure 8. Switch Sampling in Scan Mode
Table 4. Truth Table for WEN and WEND
WEN WEND WETTING CURRENT
(IN0, IN1)
16kΩ SENSE RESISTOR
(IN0, IN1)
WETTING CURRENT
(IN2–IN7)
16kΩ SENSE RESISTOR
(IN2–IN7)
0 0 Off Off Off On
0 1 Off On Off On
1 0 Off Off On On
1 1 On On On On
IN1 (see Table 4). The DO0 and DO1 outputs are three-
stated when WEND = 1. When programmed as direct
inputs (WEND = 0), any input changes on IN0 and IN1
are not reflected by the status register.
Bits 9 and 8: Switch Configuration for IN7–IN4 (M1, M0)
The M1 and M0 bits set the switch configuration in
groups of two for IN7 through IN4 (see Table 5). Set M1
to configure IN7 and IN6 for battery-connected switches
and clear M1 for ground-connected switches. Set M0 to
configure IN5 and IN4 for battery-connected switches
and clear M0 for ground-connected switches.
Bits 7–0: Interrupt Enable for IN7–IN0 (P7–P0)
The P7 through P0 bits allow independent control of
whether inputs IN7 through IN0 generate an interrupt
(INT). Set any bit to disable interrupts on the corre-
sponding input and clear the bit to enable interrupts on
the corresponding channel. An interrupt is asserted
when any input configured for interrupts changes state.
IN0 and IN1 do not generate an interrupt when confi-
gured as direct inputs (WEND = 0).
Operating Modes
The MAX13037/MAX13038 feature three modes of oper-
ation: normal mode, scan mode, and shutdown mode.
Normal mode is entered when the scanning period bits
in the command register are configured for continuous
scanning ([SC2:SC1:SC0] = [1:1:1] or [1:1:0]). Scan
mode is entered when the scanning period bits are set
for a periodic scanning time as shown in Table 3.
Shutdown mode is entered by driving the shutdown
input (SD) low. The default mode after power-up is scan
mode (when SD = high) with a scan period of 64ms.
Normal Mode (Continuous Scanning)
In normal mode, the input sense resistors are always
connected to the switch inputs to detect any input status
change (except IN0 and IN1 when WEND = [0]). Wetting
currents are enabled according to the WEN, WEND, and
WTOFF bits in the command register. If adjustable hys-
teresis is not required, this feature can be disabled to
reduce power consumption (see the
Typical Operating
Characteristics
) by setting the scanning period bits in the
command register to ([SC2:SC1:SC0] = [1:1:0]). The
hysteresis is set to 0.166 x VBATREF when adjustable
hysteresis is disabled.
Scan Mode
In scan mode, each sense resistor is connected for a
finite duration of 250µs (typ) and is repeated at a period
according to the scanning period bits SC2, SC1, and SC0
(see Table 3). All input resistors are connected simultane-
ously and the inputs are polled at the same time. When all
external switches are open and the scanning period is set
to 64ms the scanning mode reduces current consump-
tion to typically 28µA (LDO on) and 17µA (LDO off).
Wetting currents (if enabled) are applied to closed
switches during the polling time of 250µs (typ) and are
pulsed at the programmed scanning period. When
WTOFF is set, the wetting current continuously pulses at
the programmed scanning period. When WTOFF is
cleared, the wetting current pulses at the programmed
scanning period, but turns off after 20ms elapses. Inputs
IN0 and IN1 cannot be used as direct inputs (WEND = 0)
in scan mode. When configured as direct inputs in scan
mode, the outputs DO0 and DO1 are high impedance.
The quiescent current for a given scan mode can be cal-
culated by the following formula (LDO off):
Where VBAT = SD = +14V, IBAT is the BAT current
expressed in microamps and tSCAN_P is the scanning
period expressed in milliseconds.
Shutdown Mode
In shutdown mode, the LDO is disabled, all switch
inputs are high impedance and the external switches
are no longer monitored, reducing current consumption
on BAT to 2.85µA (typ). The MAX13037/MAX13038
reset upon entering shutdown mode and the contents
of the command register are lost. Exit shutdown mode
by bringing the voltage on SD above +2.4V. The SD
input is compatible with voltages up to VBAT. The
MAX13037/MAX13038 take 200µs (typ) to exit shutdown
It
BAT( A) SCAN P(ms)
μ=×+
⎛
⎝
⎜
⎞
⎠
⎟
16 1 1
_
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
______________________________________________________________________________________ 17
Table 5. Switch Configuration Controlled by M1 and M0
M1 M0 IN7 AND IN6 SWITCH
CONFIGURATION
IN5 AND IN4 SWITCH
CONFIGURATION
IN3–IN0 SWITCH
CONFIGURATION
0 0 Ground Ground Ground
0 1 Ground Battery Ground
1 0 Battery Ground Ground
1 1 Battery Battery Ground
MAX13037/MAX13038
at which point the command register is restored to its
power-up default (0x00) and the MAX13037/
MAX13038 enter scan mode. Note that SD is compati-
ble with both logic and BAT voltage levels. Having SD
compatible to VBAT allows the MAX13037/MAX13038 to
retain the settings in the command register as well as
input monitoring even when VLO is disabled, provided
that SD = VBAT.
Applications Information
Automotive Considerations
Reverse-Battery Tolerance
The BATREF and IN0–IN7 inputs can withstand voltages
down to -45V without damage so that reverse battery is
not an issue. The BAT input should be protected with a
reverse-battery diode as shown in the
Typical Application
Circuit
. The shutdown (SD) and REGON inputs can be
controlled from a battery-level source, but should be pro-
tected against reverse battery in the application.
Power Dissipation
Wetting currents and the LDO output current can result in
overheating the MAX13037/MAX13038. At the early ther-
mal warning threshold of +135°C (typ), wetting currents
are disabled. This allows the LDO output to remain
enabled if overheating is caused by the wetting currents.
At temperatures above +170°C, the LDO is also turned
off to avoid damage to the device.
It is important to consider the effects of wetting currents
on the power dissipated by the MAX13037/MAX13038.
For example, assume all inputs are configured for a
continuous wetting current of 25mA, all external switch-
es have an on-resistance of 1Ωand the battery voltage
is +16V. If all switches are simultaneously closed, the
corresponding power dissipated due to wetting currents
only is (16V - (25mA x 1Ω)) x 25mA x 8 = 3.12W, which
is higher than the absolute maximum power dissipation
of 2857mW at +70°C.
The LDO is a second source of power dissipation. For
example, if VLO = +3.3V, ILO = 100mA and VBAT =
+16V, the power dissipated by the LDO is (16V - 3.3V)
+ (0.1) = 1.27W. Both the LDO and wetting currents
should be taken into account for correct use of the
MAX13037/MAX13038.
ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electro-
static discharges encountered during handling and
assembly. The IN7–IN0 inputs have extra protection
against static electricity. Maxim’s engineers have
developed state-of-the-art structures to protect these
pins against ESD of ±8kV without damage.
Human Body Model
The MAX13037/MAX13038 IN7–IN0 pins are charac-
terized for ±8kV ESD protection using the Human
Body Model. Figure 7a shows the Human Body Model,
and Figure 7b shows the current waveform it gener-
ates when discharged into a low impedance. This
model consists of a 100pF capacitor charged to the
ESD voltage of interest, which is then discharged into
the device through a 1.5kΩresistor.
Automotive Contact Monitor and
Level Shifters with LDO Regulator
18 ______________________________________________________________________________________
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
Cs
100pF
RC 1MΩRD 1500Ω
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
Figure 7a. Human Body ESD Test Model
IP 100%
90%
36.8%
tRL TIME
tDL
CURRENT WAVEFORM
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
Ir
10%
0
0
AMPERES
Figure 7b. Human Body Model Current Waveform
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
______________________________________________________________________________________ 19
27
26
25
24
23
22
21
1
2
3
4
5
6
7
12
13
14
15
16
17
18
34
33
32
31
30
29
28
MAX13037/MAX13038
TQFN
(6mm x 6mm)
TOP VIEW
THRESH
DO0
WDI
GND
BATREF
VLO
N.C.
DO1
CLK
SDI
SD0
TD
GND
TDEB
WET
HYST
10
11
36
35
BAT
BAT
N.C.
N.C.
*EP
*CONNECT EXPOSED PADDLE TO GROUND
IN5
IN4
IN3
IN2
IN1
IN0
GND
+
INT
OT
CS
RST
20
19
8
9
IN7
IN6
SD
REGOFF
REGON
Pin Configuration
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
20 ______________________________________________________________________________________
MAX13036
IN7
IN6
IN5
IN4
IN3
IN2
IN1
IN0
0.1μF 0.1μF
47μF
BATREF
0.01μF0.01μF
BAT
MAX13037
MAX13038
IN7
IN6
IN5
IN4
IN3
IN2
IN1
4.7μF
IN0
ECU CONNECTOR
DO0
THRESH
DO1
DO0
DO1
GND
BATREF
SDI SDO
SDO SDI
WDI
CLK CLK
CS CS
BATTERY
+6V TO +26V,
+42V LOAD
DUMP
BAT
VLO
4700pF
4700pF
61kΩ
30kΩ
HYST
WET
TD
TDEB
4700pF
90kΩ
30kΩ
HYST
WET
TDEB
GND
REGOFF
REGON
SD
RST
OT
INT
VLO
0.1μF
VL
SD
OT
INT
μC
Typical Operating Circuit
Chip Information
PROCESS: BiCMOS
MAX13037/MAX13038
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
QFN THIN.EPS
Automotive Contact Monitor and
Level Shifters with LDO Regulator
______________________________________________________________________________________ 21
MAX13037/MAX13038
Automotive Contact Monitor and
Level Shifters with LDO Regulator
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
22
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
