1
LTC2902
2902f
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
Programmable Quad Supply
Monitor with Adjustable Reset Timer
and Supply Tolerance
■
Simultaneously Monitors Four Supplies
■
16 User Selectable Combinations of 5V, 3.3V, 3V,
2.5V, 1.8V, 1.5V and/or ±Adjustable Voltage
Thresholds
■
Guaranteed Threshold Accuracy: ±1.5% of Monitored
Voltage Over Temperature
■
Selectable Supply Tolerance: 5%, 7.5%,
10%, 12.5% Below Monitored Voltage
■
Low Supply Current: 43µA Typ
■
Adjustable Reset Time
■
RESET Disable Pin for Margining Applications
■
Open-Drain RST Output (LTC2902-1)
■
Push-Pull RST Output (LTC2902-2)
■
Individual Nondelayed Monitor Outputs for Each Supply
■
Power Supply Glitch Immunity
■
Guaranteed RESET for V
CC
≥ 1V
The LTC
®
2902 is a programmable supply monitor for sys-
tems with up to four supply voltages. One of 16 preset or
adjustable voltage monitor combinations can be selected
using an external resistor divider connected to the pro-
gram pin. The preset voltage thresholds are digitally pro-
grammable to 5%, 7.5%, 10% or 12.5% below the nomi-
nal operating voltage, and are accurate to 1.5% over tem-
perature. All four voltage comparator outputs are con-
nected to separate pins for individual supply monitoring.
The reset delay time is adjustable using an external
capacitor. Tight voltage threshold accuracy and glitch
immunity ensure reliable reset operation without false
triggering. The RST output is guaranteed to be in the
correct state for V
CC
down to 1V and may be disabled
during supply margin testing. The LTC2902-1 features
an open-drain RST output, while the LTC2902-2 has a
push-pull RST output.
The 43µA supply current makes the LTC2902 ideal for power
conscious systems and the part may be configured to
monitor less than four inputs. The LTC2902-1/LTC2902-2
are available in the 16-lead narrow SSOP package.
Quad Supply Monitor with Adjustable Tolerance (5V, 3.3V, 2.5V, 1.8V)
■
Desktop and Notebook Computers
■
Multivoltage Systems
■
Telecom Equipment
■
Portable Battery-Powered Equipment
■
Network Servers
, LTC and LT are registered trademarks of Linear Technology Corporation.
V1
V2
VREF
VPG
COMP1
COMP2
COMP3
COMP4
RST
RDIS
T0
T1
GND
10
11
R1
59k
1%
R3
10k POWER
GOOD
R2
40.2k
1%
12
7
9
8
6
15
1
16
2
133
14
4
5CRT
47nF
C2
0.1µF
C1
0.1µF
V4V3
LTC2902-2
CRT tRST = 216ms
MARGIN
TOLERANCE = 5%
2902 TA01
DC/DC
CONVERTER 1.8V
2.5V
3.3V
5V
SYSTEM
LOGIC
2
LTC2902
2902f
ORDER PART
NUMBER
GN16 PART MARKING
29021
29022
29021I
29022I
T
JMAX
= 125°C, θ
JA
= 130°C/W
(Notes 1, 2, 3)
V1, V2, V3, V4, V
PG
..................................... –0.3V to 7V
RST (LTC2902-1)........................................ –0.3V to 7V
RST (LTC2902-2).......................... –0.3V to (V2 + 0.3V)
COMPX, RDIS ............................................. –0.3V to 7V
T0, T1 .......................................... –0.3V to (V
CC
+ 0.3V)
CRT ............................................. –0.3V to (V
CC
+ 0.3V)
V
REF
............................................. –0.3V to (V
CC
+ 0.3V)
Reference Load Current (I
VREF
) ............................ ±1mA
V4 Input Current (–ADJ Mode) ............................ –1mA
Operating Temperature Range
LTC2902-1C/LTC2902-2C ....................... 0°C to 70°C
LTC2902-1I/LTC2902-2I .................... –40°C to 85°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
LTC2902-1CGN
LTC2902-2CGN
LTC2902-1IGN
LTC2902-2IGN
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
T0
RDIS
COMP2
COMP4
V2
V4
VREF
VPG
GND
T1
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
RT50
5V, 5% Reset Threshold V1 Input Threshold ●4.600 4.675 4.750 V
5V, 7.5% Reset Threshold ●4.475 4.550 4.625 V
5V, 10% Reset Threshold ●4.350 4.425 4.500 V
5V, 12.5% Reset Threshold ●4.225 4.300 4.375 V
V
RT33
3.3V, 5% Reset Threshold V1, V2 Input Threshold ●3.036 3.086 3.135 V
3.3V, 7.5% Reset Threshold ●2.954 3.003 3.053 V
3.3V, 10% Reset Threshold ●2.871 2.921 2.970 V
3.3V, 12.5% Reset Threshold ●2.789 2.838 2.888 V
V
RT30
3V, 5% Reset Threshold V2 Input Threshold ●2.760 2.805 2.850 V
3V, 7.5% Reset Threshold ●2.685 2.730 2.775 V
3V, 10% Reset Threshold ●2.610 2.655 2.700 V
3V, 12.5% Reset Threshold ●2.535 2.580 2.625 V
V
RT25
2.5V, 5% Reset Threshold V2, V3 Input Threshold ●2.300 2.338 2.375 V
2.5V, 7.5% Reset Threshold ●2.238 2.275 2.313 V
2.5V, 10% Reset Threshold ●2.175 2.213 2.250 V
2.5V, 12.5% Reset Threshold ●2.113 2.150 2.188 V
V
RT18
1.8V, 5% Reset Threshold V3, V4 Input Threshold ●1.656 1.683 1.710 V
1.8V, 7.5% Reset Threshold ●1.611 1.638 1.665 V
1.8V, 10% Reset Threshold ●1.566 1.593 1.620 V
1.8V, 12.5% Reset Threshold ●1.521 1.548 1.575 V
V
RT15
1.5V, 5% Reset Threshold V3, V4 Input Threshold ●1.380 1.403 1.425 V
1.5V, 7.5% Reset Threshold ●1.343 1.365 1.388 V
1.5V, 10% Reset Threshold ●1.305 1.328 1.350 V
1.5V, 12.5% Reset Threshold ●1.268 1.290 1.313 V
V
RTA
ADJ, 5% Reset Threshold V3, V4 Input Threshold ●0.492 0.500 0.508 V
ADJ, 7.5% Reset Threshold ●0.479 0.487 0.494 V
ADJ, 10% Reset Threshold ●0.466 0.473 0.481 V
ADJ, 12.5% Reset Threshold ●0.453 0.460 0.467 V
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Note 3)
ELECTRICAL CHARACTERISTICS
3
LTC2902
2902f
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Note 3)
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: All voltage values are with respect to GND.
Note 3: The greater of V1, V2 is the internal supply voltage (V
CC
).
Note 4: Under static no-fault conditions, V1 will necessarily supply quiescent
current. If at any time V2 is larger than V1, V2 must be capable of supplying
the quiescent current, programming (transient) current and reference load
current.
Note 5: The output pins RST and COMPX have internal pull-ups to V2 of
typically 6µA. However, external pull-up resistors may be used when faster
rise times are required or for V
OH
voltages greater than V2.
Note 6: The push-pull RST output pin on the LTC2902-2 is
actively
pulled up
to V2.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
RTAN
–ADJ Reset Threshold V4 Input Threshold ●–18 0 18 mV
V
CC
Minimum Internal Operating Voltage RST, COMPX in Correct Logic State; ●1V
V
CC
Rising Prior to Program
V
CCMINP
Minimum Required for Programming V
CC
Rising ●2.42 V
V
CCMINC
Minimum Required for Comparators V
CC
Falling ●2.32 V
V
REF
Reference Voltage V
CC
≥ 2.3V, I
VREF
= ±1mA, C
REF
≤ 1000pF
T0 Low, T1 Low ●1.192 1.210 1.228 V
T0 Low, T1 High ●1.160 1.178 1.195 V
T0 High, T1 Low ●1.128 1.146 1.163 V
T0 High, T1 High ●1.096 1.113 1.130 V
V
PG
Programming Voltage Range V
CC
≥ V
CCMINP
●0V
REF
V
I
VPG
V
PG
Input Current V
PG
= V
REF
●±20 nA
I
V1
V1 Input Current V1 = 5V, I
VREF
= 12µA, (Note 4) ●43 75 µA
I
V2
V2 Input Current V2 = 3.3V ●0.8 2 µA
I
V3
V3 Input Current V3 = 2.5V ●0.52 1.2 µA
V3 = 0.55V (ADJ Mode) –15 15 nA
I
V4
V4 Input Current V4 = 1.8V ●0.34 0.8 µA
V4 = 0.55V (ADJ Mode) ●–15 15 nA
V4 = –0.05V (–ADJ Mode) ●–15 15 nA
I
CRT(UP)
CRT Pull-Up Current V
CRT
= 0V ●–1.4 –2 –2.6 µA
I
CRT(DN)
CRT Pull-Down Current V
CRT
= 1.3V ●10 20 30 µA
t
RST
Reset Time-Out Period C
RT
= 1500pF ●579 ms
t
UV
V
X
Undervoltage Detect to RST or COMPX V
X
Less Than Reset Threshold V
RTX
150 µs
by More Than 1%
V
OL
Output Voltage Low RST, COMPX I
SINK
= 2.5mA; V1 = 3V, V2 = 3V; ●0.15 0.4 V
V3, V4 = 0V; V
PG
= 0V
I
SINK
= 100µA; V2 = 1V; V1, V3, V4 = 0V ●0.05 0.3 V
I
SINK
= 100µA; V1 = 1V; V2, V3, V4 = 0V ●0.05 0.3 V
V
OH
Output Voltage High RST, COMPX (Note 5) I
SOURCE
= 1µA●V2 – 1 V
V
OH
Output Voltage High RST (LTC2902-2) I
SOURCE
= 200µA●0.8 • V2 V
(Note 6)
Digital Inputs T0, T1, RDIS
V
IL
T0, T1 Low Level Input Voltage V
CC
= 3.3V to 5.5V ●0.3V
CC
V
V
IH
T0, T1 High Level Input Voltage V
CC
= 3.3V to 5.5V ●0.7V
CC
V
I
INTOL
T0, T1 Input Current T0 = 0V, T1 = V
CC
●±0.1 ±1µA
V
IL
RDIS Input Threshold Low V
CC
= 3.3V to 5.5V ●0.4 V
V
IH
RDIS Input Threshold High V
CC
= 3.3V to 5.5V ●1.6 V
I
RDIS
RDIS Pull-Up Current V
RDIS
= 0V –10 µA
4
LTC2902
2902f
TEST CIRCUITS
TI I G DIAGRA
UWW
TYPICAL PERFOR A CE CHARACTERISTICS
UW
V1
V2
V3
V4
2902 F01
LTC2902-1 RST
OR COMPX
I
SOURCE
1µA
V1
V2
V3
V4
2902 F02
LTC2902-1 ISINK
2.5mA,
100µA
RST
OR COMPX
V1
V2
V3
V4
2902 F03
LTC2902-2 RST
I
SOURCE
200µA
Figure 1. RST, COMPX VOH Test Figure 2. RST, COMPX VOL Test Figure 3. Active Pull-Up RST VOH Test
t
RST
2902 TD
V
RTX
V
X
RST
COMPX
t
UV
1.5V
VX Monitor Timing
5V Threshold Voltage
vs Temperature
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RT50
(V)
4.75
4.70
4.65
4.60
4.55
4.50
4.45
4.40
4.35
4.30
4.25 –20 20 40
2902 G01
–40 0 60 80 100
5%
7.5%
10%
12.5%
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RT33
(V)
3.135
3.100
3.065
3.030
2.995
2.960
2.925
2.890
2.855
2.820
2.785 –20 20 40
2902 G02
–40 0 60 80 100
5%
7.5%
10%
12.5%
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RT30
(V)
2.850
2.815
2.780
2.745
2.710
2.675
2.640
2.605
2.570
2.535 –20 20 40
2902 G03
–40 0 60 80 100
5%
7.5%
10%
12.5%
3.3V Threshold Voltage
vs Temperature 3V Threshold Voltage
vs Temperature
5
LTC2902
2902f
2.5V Threshold Voltage
vs Temperature 1.8V Threshold Voltage
vs Temperature 1.5V Threshold Voltage
vs Temperature
ADJ Threshold Voltage
vs Temperature –ADJ Threshold Voltage
vs Temperature
IV1 vs Temperature
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RT25
(V)
2.375
2.350
2.325
2.300
2.275
2.250
2.225
2.200
2.175
2.150
2.125
2.100 –20 20 40
2902 G04
–40 0 60 80 100
5%
7.5%
10%
12.5%
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, VRT18 (V)
1.710
1.685
1.660
1.635
1.610
1.585
1.560
1.535
1.510 –20 20 40
2902 G05
–40 0 60 80 100
5%
7.5%
10%
12.5%
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RT15
(V)
1.425
1.405
1.385
1.365
1.345
1.325
1.305
1.285
1.265 –20 20 40
2902 G06
–40 0 60 80 100
5%
7.5%
10%
12.5%
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, V
RTA
(V)
0.508
0.503
0.498
0.493
0.488
0.483
0.478
0.473
0.468
0.463
0.458
0.453 –20 20 40
2902 G07
–40 0 60 80 100
5%
7.5%
10%
12.5%
VREF vs Temperature
IV2 vs Temperature IV3 vs Temperature
TEMPERATURE (°C)
–60
THRESHOLD VOLTAGE, VRTAN (V)
0.018
0.012
0.006
0
–0.006
–0.012
–0.018 –20 20 40
2902 G08
–40 0 60 80 100
TEMPERATURE (°C)
–60
VREF (V)
1.228
1.216
1.204
1.192
1.180
1.168
1.156
1.144
1.132
1.112
1.108
1.096 –20 20 40
2902 G09
–40 0 60 80 100
5%
7.5%
10%
12.5%
TEMPERATURE (°C)
–60
0
I
V1
(µA)
10
30
40
50
100
70
–20 20 40
2902 G10
20
80
90
60
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
TEMPERATURE (°C)
–60
0.5
I
V2
(µA)
0.6
0.8
0.9
1.0
1.5
1.2
–20 20 40
2902 G11
0.7
1.3
1.4
1.1
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
TEMPERATURE (°C)
–60
0.1
I
V3
(µA)
0.2
0.4
0.5
0.6
1.1
0.8
–20 20 40
2902 G12
0.3
0.9
1.0
0.7
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
6
LTC2902
2902f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Typical Transient Duration
vs Comparator Overdrive (V1, V2)
RST Output Voltage
vs V1, VPG = 0V Reset Time-Out Period
vs Temperature Reset Time-Out Period
vs Capacitance
IV4 vs Temperature
RST, COMPX ISINK
vs Supply Voltage
TEMPERATURE (°C)
–60
0
I
V4
(µA)
0.1
0.3
0.4
0.5
1.0
0.7
–20 20 40
2902 G13
0.2
0.8
0.9
0.6
–40 0 60 80 100
V1 = 5V
V2 = 3.3V
V3 = 2.5V
V4 = 1.8V
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V
RTX
)
0.1
250
TYPICAL TRANSIENT DURATION (µs)
300
350
400
450
1 10 100
2902 G14
200
150
50
0
100
RESET OCCURS
ABOVE CURVE
T
A
= 25°C
V1 (V)
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
RST OUTPUT VOLTAGE (V)
2902 G15
5
4
3
2
1
0
V1 = V2 = V3 = V4
10k PULL-UP FROM RST TO V1
TA = 25°C
TEMPERATURE (°C)
–60
4.9
RESET TIME-OUT PERIOD, t
RST
(ms)
5.9
6.4
6.9
8.9
7.9
–20 20 40
2902 G16
5.4
8.4
7.4
–40 0 60 80 100
C
RT
= 1500pF
(SILVER MICA)
CRT (FARAD)
10p 100p 10n 1µ
10
1
100m
10m
1m
100µ
2902 G17
1n 100n
RESET TIME-OUT PERIOD, tRST (sec)
TA = 25°C
V1 OR V2 (V)
0
0
ISINK (mA)
2
4
6
1234
2902 G18
5
8
10
1
3
5
7
9
6
VOL = 0.4V
TA = 25°C
VOL = 0.2V
RST, COMPX Voltage Output Low
vs Output Sink Current
RST High Level Output Voltage
vs Output Source Current
(LTC2902-2)
I
SINK
(mA)
0
V
OL
(V)
20 40 50 90
2902 G19
10 30 60 70 80
3.0
2.5
2.0
1.5
1.0
0.5
0
85°C
25°C
–40°C
V2 = 3V
V1 = 5V
ISOURCE (mA)
0 0.5 2
VOH (V)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
2902 G20
2.5
1.51
85°C
25°C
–40°C
V1 = 5V
V2 = 3V
V3 = 2.5V
V4 = 1V
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V
RTX
)
0.1
80
TYPICAL TRANSIENT DURATION (µs)
100
120
140
160
1 10 100
2902 G25
60
40
20
0
200
180
220 T
A
= 25°C
RESET OCCURS
ABOVE CURVE
Typical Transient Duration
vs Comparator Overdrive (V3, V4)
7
LTC2902
2902f
UU
U
PI FU CTIO S
COMP3 (Pin 1): Comparator Output 3. Nondelayed, active
high logic output with weak pull-up to V2. Pulls high when
V3 is above reset threshold. May be pulled greater than V2
using external pull-up.
COMP1 (Pin 2): Comparator Output 1. Nondelayed, active
high logic output with weak pull-up to V2. Pulls high when
V1 is above reset threshold. May be pulled greater than V2
using external pull-up.
V3 (Pin 3): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V
or ADJ. See Table 1 for details.
V1 (Pin 4): Voltage Input 1. Select from 5V or 3.3V. See
Table 1 for details. The greater of (V1, V2) is also V
CC
for
the chip. Bypass this pin to ground with a 0.1µF (or
greater) capacitor.
CRT (Pin 5): Reset Delay Time Programming Pin. Attach
an external capacitor (C
RT
) to GND to set a reset delay time
of 4.6ms/nF. Leaving the pin open generates a minimum
delay of approximately 50µs. A 47nF capacitor will gener-
ate a 216ms reset delay time.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
RST Pull-Up Current vs V2
(LTC2902-1) RST Pull-Up Current vs V2
(LTC2902-2)
INPUT OVERDRIVE ABOVE THRESHOLD (mV)
COMPX PROPAGATION DELAY (µs)
250
200
V1, V2
V3, V4
150
2902 G22
0
100
50
1000
10 100
T
A
= 25°C
V2 (V)
2
0
PULL-UP CURRENT (µA)
4
8
12
2.5 33.5 4
2902 G23
4.5
16
20
2
6
10
14
18
5
TA = 25°C
VRT25
VRT30
VRT33
V2 (V)
2
0
PULL-UP CURRENT (mA)
2
4
5
2.5 33.5 4
2902 G24
4.5
1
3
6
5
T
A
= 25°C
V
RT25
V
RT30
V
RT33
COMPX Propagation Delay vs
Input Overdrive Above Threshold
COMPX Pull-Up Current
vs V2 (COMPX Held at 0V)
V2 (V)
1
0
PULL-UP CURRENT (µA)
2
6
8
10
20
14
233.5
2902 G21
4
16
18
12
1.5 2.5 44.5 5
T
A
= 25°C
8
LTC2902
2902f
UU
U
PI FU CTIO S
RST (Pin 6): Reset Logic Output. Active low with weak
pull-up to V2 (LTC2902-1) or active pull-up to V2
(LTC2902-2). Pulls low when any voltage input is below
the reset threshold and held low for programmed delay
time after all voltage inputs are above threshold. May be
pulled above V2 using an external pull-up (LTC2902-1
only).
T0 (Pin 7): Digital Input for Supply Tolerance Selection
(5%, 7.5%, 10% or 12.5%). Used in conjunction with T1
(Pin 9). See Applications Information for tolerance selec-
tion chart (Table 4).
RDIS (Pin 8): Digital Input for RST Disable. A low input on
this pin forces the RST output to V2 (or pull-up voltage).
Useful for determining supply margins without issuing
reset command to processor. A weak internal pull-up
allows pin to be left floating for normal monitor operation.
T1 (Pin 9): Digital Input for Supply Tolerance Selection
(5%, 7.5%, 10% or 12.5%). Used in conjunction with T0
(Pin 7). See Applications Information for tolerance selec-
tion chart (Table 4).
GND (Pin 10): Ground.
V
PG
(Pin 11):
Voltage Threshold Combination Select
Input. Connect to an external 1% resistive divider be-
tween VREF and GND to select 1 of 16 combinations of
preset and/or ±adjustable voltage thresholds (see Table␣ 1).
Do not add capacitance on the VPG pin.
VREF (Pin 12): Buffered Reference Voltage. A 1.210V
nominal reference used for programming voltage (VPG)
and for the offset of negative adjustable applications. The
buffered reference can source and sink up to 1mA. The
reference can drive a bypass capacitor of up to 1000pF
without oscillation.
V4 (Pin 13): Voltage Input 4. Select from 1.8V, 1.5V, ADJ
or –ADJ. See Table 1 for details.
V2 (Pin 14): Voltage Input 2. Select from 3.3V, 3V or 2.5V.
See Table 1 for details. The greater of (V1, V2) is also V
CC
for chip. Bypass this pin to ground with a 0.1µF (or greater)
capacitor. All logic outputs (COMP1, COMP2, COMP3,
COMP4) are weakly pulled up to V2. RST is weakly pulled
up to V2 in the LTC2902-1 and RST is actively pulled up to
V2 in the LTC2902-2.
COMP4 (Pin 15): Comparator Output 4. Nondelayed,
active high logic output with weak pull-up to V2. Pulls high
when V4 is above reset threshold. May be pulled greater
than V2 using external pull-up.
COMP2 (Pin 16): Comparator Output 2. Nondelayed,
active high logic output with weak pull-up to V2. Pulls high
when V2 is above reset threshold. May be pulled greater
than V2 using external pull-up.
9
LTC2902
2902f
–
+
–
+
–
+
–
+
4
14
3
13
V1
V2
V3
RESISTIVE
DIVIDER
MATRIX
V4
10
GND
A/D
BUFFER
11
VPG
12
VREF
5CRT
CRT
BANDGAP
REFERENCE
ADJUSTABLE
RESET PULSE
GENERATOR
BUFFER
GAIN
ADJUST
POWER
DETECT
V1
V2
VCC
6
RST
V2
22µA
VCC
8RDIS
2µA
10µA
15
COMP4
V2
6µA
6µA
VCC
LTC2902-1
1
COMP3
V2
6µA
16
COMP2
V2
6µA
2
COMP1
V2
6µA
9T1
7T0
2902 DB-1
6
RST
V2
LTC2902-2
BLOCK DIAGRA
W
10
LTC2902
2902f
APPLICATIO S I FOR ATIO
WUUU
Power-Up
On power-up, the larger of V1 or V2 will power the drive
circuits for the RST and the COMPX pins. This ensures
that the RST and COMPX outputs will be low as soon as
V1 or V2 reaches 1V. The RST and COMPX outputs will
remain low until the part is programmed. After program-
ming, if any one of the V
X
inputs is below its programmed
threshold, RST will be a logic low. Once all the V
X
inputs
rise above their thresholds, an internal timer is started
and RST is released after the programmed delay time. If
V
CC
< (V3 – 1) and V
CC
< 2.4V, the V3 input impedance
will be low (1kΩ typ).
Monitor Programming
The LTC2902 input voltage combination is selected by
placing the recommended resistor divider from VREF to
GND and connecting the tap point to VPG, as shown in
Figure 4. Table 1 offers recommended 1% resistor values
for the various modes. The last column in Table 1 speci-
fies optimum VPG/VREF ratios (±0.01) to be used when
pro
gramming with a ratiometric DAC.
During power-up, once V1 or V2 reaches 2.4V (max), the
monitor enters a programming period of approximately
150µs during which the voltage on the V
PG
pin is sampled
and the monitor is configured to the desired input combi-
nation. Do not add capacitance to the V
PG
pin. Immediately
after programming, the comparators are enabled and
supply monitoring will begin.
Supply Monitoring
The LTC2902 is a low power, high accuracy program-
mable quad supply monitoring circuit with four nondelayed
monitor outputs, a common reset output and selectable
supply thresholds. Reset timing is adjustable using an
external capacitor. Single pin programming selects 1 of 16
input voltage monitor combinations. Two digital inputs
select one of four supply tolerances (5%, 7.5%, 10% or
12.5%). All four voltage inputs must be above predeter-
mined thresholds for the reset not to be invoked. The
LTC2902 will assert the reset and comparator outputs
during power-up, power-down and brownout conditions
on any one of the voltage inputs.
Table 1. Voltage Threshold Programming
V
PG
MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ)V
REF
0 5.0 3.3 ADJ ADJ Open Short 0.000
1 5.0 3.3 ADJ –ADJ 93.1 9.53 0.094
2 3.3 2.5 ADJ ADJ 86.6 16.2 0.156
3 3.3 2.5 ADJ –ADJ 78.7 22.1 0.219
4 3.3 2.5 1.5 ADJ 71.5 28.0 0.281
5 5.0 3.3 2.5 ADJ 66.5 34.8 0.344
6 5.0 3.3 2.5 1.8 59.0 40.2 0.406
7 5.0 3.3 2.5 1.5 53.6 47.5 0.469
8 5.0 3.0 2.5 ADJ 47.5 53.6 0.531
9 5.0 3.0 ADJ ADJ 40.2 59.0 0.594
10 3.3 2.5 1.8 1.5 34.8 66.5 0.656
11 3.3 2.5 1.8 ADJ 28.0 71.5 0.719
12 3.3 2.5 1.8 –ADJ 22.1 78.7 0.781
13 5.0 3.3 1.8 –ADJ 16.2 86.6 0.844
14 5.0 3.3 1.8 ADJ 9.53 93.1 0.906
15 5.0 3.0 1.8 ADJ Short Open 1.000
Figure 4. Monitor Programming
12
11
10
R1
1%
R2
1%
2902 F04
V
REF
V
PG
GND
LTC2902
The inverting inputs on the V3 and/or V4 comparators are
set to 0.5V when the positive adjustable modes are selected
and with T0 and T1 low (5% tolerance) (Figure 5). The tap
point on an external resistive divider, connected between
the positive voltage being sensed and ground, is connected
to the high impedance noninverting inputs (V3, V4). The
trip voltage is calculated from:
VV
R
R
TRIP =+
05 1 3
4
.
Once the resistor divider is set in the 5% tolerance mode,
there is no need to change the divider for the other
tolerance modes (7.5%, 10%, 12.5%) because the inter-
nal reference is scaled accordingly, moving the trip point
in –2.5% increments.
11
LTC2902
2902f
APPLICATIO S I FOR ATIO
WUUU
In the negative adjustable mode, the noninverting input on
the V4 comparator is connected to ground (Figure 6). The
tap point on an external resistive divider, connected be-
tween the negative voltage being sensed and the V
REF
pin,
is connected to the high impedance inverting input (V4).
V
REF
provides the necessary level shift required to operate
at ground. The trip voltage is calculated from:
VV
R
RVV
TRIP REF REF
=
=–;.
3
41 210
T0,T1 Low (5% Tolerance Mode)
Once the resistor divider is set in the 5% tolerance mode,
there is no need to change the divider for the other
tolerance modes (7.5%, 10%, 12.5%) because V
REF
is
scaled accordingly, moving the trip point in –2.5%
increments.
In a negative adjustable application, the minimum value
for R4 is limited by the sourcing capability of V
REF
(±1mA).
With no other load on V
REF
, R4 (minimum) is:
1.21V ÷ 1mA = 1.21kΩ
Tables 2 and 3 offer suggested 1% resistor values for
various adjustable applications.
Although all four supply monitor comparators have built-in
glitch immunity, bypass capacitors on V1 and V2 are
recommended because the greater of V1 or V2 is also the
V
CC
for the chip. Filter capacitors on the V3 and V4 inputs
are allowed.
Power-Down
On power-down, once any of the V
X
inputs drop below
their threshold, RST and COMPX are held at a logic low.
A logic low of 0.4V is guaranteed until both V1 and V2
drop below 1V. If the bandgap reference becomes invalid
(V
CC
< 2V typ), the part will reprogram once V
CC
rises
above 2.4V (max).
Monitor Output Rise and Fall Time Estimation
All of the outputs (RST, COMPX) have strong pull-down
capability. If the external load capacitance (C
LOAD
) for a
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
V
SUPPLY
(V) V
TRIP
(V) R3 (kΩ) R4 (kΩ)
12 11.25 2150 100
10 9.4 1780 100
8 7.5 1400 100
7.5 7 1300 100
6 5.6 1020 100
5 4.725 845 100
3.3 3.055 511 100
3 2.82 464 100
2.5 2.325 365 100
1.8 1.685 237 100
1.5 1.410 182 100
1.2 1.120 124 100
1 0.933 86.6 100
0.9 0.840 68.1 100
Table 3. Suggested 1% Resistor Values for the –ADJ Input
V
SUPPLY
(V) V
TRIP
(V) R3 (kΩ) R4 (kΩ)
–2 –1.87 187 121
–5 –4.64 464 121
–5.2 –4.87 487 121
–10 –9.31 931 121
–12 –11.30 1130 121
Figure 5. Setting the Positive Adjustable Trip Point
Figure 6. Setting the Negative Adjustable Trip Point
–
+
2902 F06
V4
V
REF
13
12
V
TRIP
R4
1%
R3
1%
LTC2902
–
+
+
–0.5V
5% TOLERANCE MODE
2902 F05
V3 OR V4
VTRIP
R3
1%
R4
1%
LTC2902
12
LTC2902
2902f
APPLICATIO S I FOR ATIO
WUUU
particular output is known, output fall time (10% to 90%)
is estimated using:
t
FALL
≈ 2.2 • R
PD
• C
LOAD
where R
PD
is the on-resistance of the internal pull-down
transistor. The typical performance curve (V
OL
vs I
SINK
)
demonstrates that the pull-down current is somewhat
linear versus output voltage. Using the 25°C curve, R
PD
is
estimated to be approximately 40Ω. Assuming a 150pF
load capacitance, the fall time is about 13.2ns.
Although the outputs are considered to be “open-drain,”
they do have a weak pull-up capability (see COMPX or RST
Pull-Up Current vs V2 curve). Output rise time (10% to
90%) is estimated using:
t
RISE
≈ 2.2 • R
PU
• C
LOAD
where R
PU
is the on-resistance of the pull-up transistor.
The on-resistance as a function of the V2 voltage at room
temperature is estimated using:
RV
PU
=Ω
610
21
5
•
–
with V2 = 3.3V, R
PU
is about 260k. Using 150pF for load
capacitance, the rise time is 86µs. If the output needs to
pull up faster and/or to a higher voltage, a smaller
external pull-up resistor may be used. Using a 10k pull-
up resistor, the rise time is reduced to 3.3µs for a 150pF
load capacitance.
The LTC2902-2 has an active pull-up to V2 on the RST
output. The typical performance curve (RST Pull-Up Cur-
rent vs V2 curve) demonstrates that the pull-up current is
somewhat linear versus the V2 voltage and R
PU
is esti-
mated to be approximately 625Ω. A 150pF load capaci-
tance makes the rise time about 206ns.
Selecting the Reset Timing Capacitor
The reset time-out period is adjustable in order to accom-
modate a variety of microprocessor applications. The
reset time-out period, t
RST
, is adjusted by connecting a
capacitor, C
RT
, between the CRT pin and ground. The value
of this capacitor is determined by:
C
RT
= t
RST
• 217 • 10
–9
with C
RT
in Farads and t
RST
in seconds. The C
RT
value per
millisecond of delay can also be expressed as C
RT
/ms =
217 (pF/ms).
Leaving the CRT pin unconnected will generate a mini-
mum reset time-out of approximately 50µs. Maximum
reset time-out is limited by the largest available low
leakage capacitor. The accuracy of the time-out period will
be affected by capacitor leakage (the nominal charging
current is 2µA) and capacitor tolerance. A low leakage
ceramic capacitor is recommended.
Tolerance Programming and the RESET Disable
Using the two digital inputs T0 and T1, the user can
program the global supply tolerance for the LTC2902 (5%,
7.5%, 10%, 12.5%). The larger tolerances provide more
headroom by lowering the trip thresholds.
Table 4. Tolerance Programming
T0 T1 TOLERANCE (%) V
REF
(V)
Low Low 5 1.210
Low High 7.5 1.178
High Low 10 1.146
High High 12.5 1.113
Under conventional operation, RST and COMPX will go
low when V
X
is below its threshold. At any time, the RDIS
pin can be pulled low, overriding the reset operation and
forcing the RST pin high. This feature is useful when
determining supply margins under processor control since
the reset command will not be invoked. The RDIS pin is
connected to a weak internal pull-up to V
CC
(10µA typ),
allowing the pin to be left floating if unused.
Ensuring RST Valid for V
CC
Down to 0V (LTC2902-2)
When V
CC
is below 1V the RST pull-down capability is
drastically reduced. The RST pin may float to undeter-
mined voltages when connected to high impedance (such
as CMOS logic inputs). The addition of a pull-down resis-
tor from RST to ground will provide a path for stray charge
and/or leakage currents. The resistor value should be
small enough to provide effective pull-down without ex-
cessively loading the pull-up circuitry. Too large a value
may not pull down well enough. A 100k resistor from RST
to ground is satisfactory for most applications.
13
LTC2902
2902f
Quad Supply Monitor, 5% Tolerance
5V, 3V, 1.8V, 12V (ADJ)
TYPICAL APPLICATIO S
U
5V, –5V Monitor with Unused V2, V3 Inputs Pulled
Above Trip Thresholds (5% Tolerance)
COMP2
COMP4
V2
V4
V
REF
V
PG
GND
T1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
T0
RDIS
R4
121k
1%
R3
464k
1%
SYSTEM
RESET
–5V
5V
R2
86.6k
1%
R1
16.2k
1%
LTC2902
V
TRIP
= –4.64V
2902 TA03
C
RT
COMP2
COMP4
V2
V4
VREF
VPG
GND
T1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
T0
RDIS
R3
2.15M
1%
SYSTEM
RESET
1.8V 3V
12V
5V
CRT
R4
100k
1%
LTC2902
VTRIP = 11.25V
2902 TA02
14
LTC2902
2902f
TYPICAL APPLICATIO S
U
Quad Supply Monitor with LED Undervoltage Indicators,
12.5% Tolerance, Reset Disabled
5V, 3.3V, 2.5V, 1.5V
COMP2
COMP4
V2
V4
V
REF
V
PG
GND
T1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
COMP3
COMP1
V3
V1
CRT
RST
T0
RDIS
1.5V
3.3V
5V
2.5V
R2
47.5k
1%
R1
53.6k
1%
R
L2
1k
LED
LTC2902
2902 TA04
C
RT
R
L4
1k
LED
R
L3
1k
LED
R
L1
1k
LED
15
LTC2902
2902f
U
PACKAGE DESCRIPTIO
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
GN16 (SSOP) 0502
12
345678
.229 – .244
(5.817 – 6.198)
.150 – .157**
(3.810 – 3.988)
16 15 14 13
.189 – .196*
(4.801 – 4.978)
12 11 10 9
.016 – .050
(0.406 – 1.270)
.015 ± .004
(0.38 ± 0.10) × 45°
0° – 8° TYP
.007 – .0098
(0.178 – 0.249)
.053 – .068
(1.351 – 1.727)
.008 – .012
(0.203 – 0.305)
.004 – .0098
(0.102 – 0.249)
.0250
(0.635)
BSC
.009
(0.229)
REF
.254 MIN
RECOMMENDED SOLDER PAD LAYOUT
.150 – .165
.0250 TYP.0165 ±.0015
.045 ±.005
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
INCHES
(MILLIMETERS)
NOTE:
1. CONTROLLING DIMENSION: INCHES
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
16
LTC2902
2902f
PART NUMBER DESCRIPTION COMMENTS
LTC690 5V Supply Monitor, Watchdog Timer and Battery Backup 4.65V Threshold
LTC694-3.3 3.3V Supply Monitor, Watchdog Timer and Battery Backup 2.9V Threshold
LTC699 5V Supply Monitor and Watchdog Timer 4.65V Threshold
LTC1232 5V Supply Monitor, Watchdog Timer and Push-Button Reset 4.37V/4.62V Threshold
LTC1326 Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ 4.725V, 3.118V, 1V Thresholds (±0.75%)
LTC1326-2.5 Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and ADJ 2.363V, 3.118V, 1V Thresholds (±0.75%)
LTC1536 Precision Triple Supply Monitor for PCI Applications Meets PCI t
FAIL
Timing Specifications
LTC1726-2.5 Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ Adjustable RESET and Watchdog Time-Outs
LTC1726-5 Micropower Triple Supply Monitor for 5V, 3.3V and ADJ Adjustable RESET and Watchdog Time-Outs
LTC1727-2.5/LTC1727-5 Micropower Triple Supply Monitor with Open-Drain Reset Individual Monitor Outputs in MSOP
LTC1728-1.8/LTC1728-3.3 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package
LTC1728-2.5/LTC1728-5 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package
LTC1985-1.8 Micropower Triple Supply Monitor with Push-Pull Reset Output 5-Lead SOT-23 Package
LTC2900 Programmable Quad Supply Monitor Adjustable RESET, 10-Lead MSOP Package
LTC2901 Programmable Quad Supply Monitor Adjustable RESET and Watchdog Timer,
16-Lead SSOP Package
LT/TP 1002 2K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2002
RELATED PARTS
TYPICAL APPLICATIO
U
Quad Supply Monitor with Hysteresis
5% Tolerance (Supplies Rising)
12.5% Tolerance (After RST Goes High)
COMP1
COMP2
COMP3
COMP4
RST
T0
T1
CRT
4
14
3
13
8
12
11
10
2
16
1
15
6
7
9
5
V1
V2
V3
V4
RDIS
V
REF
V
PG
GND
5V
3.3V
2.5V
1.8V
C
RT
10k
R1
59k
1%
R2
40.2k
1%
LTC2902-1
2902 TA05
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
