AVAILABLE
Functional Diagrams
Pin Configurations appear at end of data sheet.
Functional Diagrams continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
EVALUATION KIT AVAILABLE
General Description
The MAX712/MAX713 fast-charge Nickel Metal Hydride
(NiMH) and Nickel Cadmium (NiCd) batteries from a DC
source at least 1.5V higher than the maximum battery
voltage. 1 to 16 series cells can be charged at rates up
to 4C. A voltage-slope detecting analog-to-digital convert-
er, timer, and temperature window comparator determine
charge completion. The MAX712/MAX713 are powered
by the DC source via an on-board +5V shunt regulator.
They draw a maximum of 5µA from the battery when not
charging. A low-side current-sense resistor allows the
battery charge current to be regulated while still
supplying power to the battery’s load.
The MAX712 terminates fast charge by detecting zero
voltage slope, while the MAX713 uses a negative
voltage-slope detection scheme. Both parts come in 16-
pin DIP and SO packages. An external power PNP tran-
sistor, blocking diode, three resistors, and three
capacitors are the only required external components.
The evaluation kit is available: Order the MAX712EVKIT-
DIP for quick evaluation of the linear charger.
________________________Applications
Battery-Powered Equipment
Laptop, Notebook, and Palmtop Computers
Handy-Terminals
Cellular Phones
Portable Consumer Products
Portable Stereos
Cordless Phones
Features
♦Fast-Charge NiMH or NiCd Batteries
♦Voltage Slope, Temperature, and Timer
Fast-Charge Cutoff
♦Charge 1 to 16 Series Cells
♦Supply Battery’s Load While Charging
(Linear Mode)
♦Fast Charge from C/4 to 4C Rate
♦C/16 Trickle-Charge Rate
♦Automatically Switch from Fast to Trickle Charge
♦Linear Mode Power Control
♦5µA (max) Drain on Battery when Not Charging
♦5V Shunt Regulator Powers External Logic
NiCd/NiMH Battery
Fast-Charge Controllers
MAX712
MAX713
THI
R2
150Ω
R3
68kΩ
R4
22kΩ
R1
10μF
C4
0.01μF
C1
1μF
C3
10μF
C2
0.01μF
DRV
Q1
2N6109
DC IN
WALL
CUBE
D1
1N4001
BATTERY
RSENSE
V+
VLIMIT BATT+
REF
TEMP
BATT- TLO GNDCC
LOAD
Typical Operating Circuit
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
REF
V+
DRV
GND
BATT-
CC
PGM3
PGM2
VLIMIT
BATT+
PGM0
PGM1
THI
TLO
TEMP
FASTCHG
TOP VIEW
MAX712
MAX713
DIP/SO
Pin Configuration
19-0100; Rev 6; 12/08
PART
MAX712CPE
MAX712CSE
MAX712C/D 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP RANGE PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
Ordering Information
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
**Contact factory for availability and processing to MIL-STD-883.
MAX712EPE
MAX712ESE
MAX712MJE -55°C to +125°C
-40°C to +85°C
-40°C to +85°C 16 Plastic DIP
16 Narrow SO
16 CERDIP**
MAX712/MAX713
NiCd/NiMH Battery
Fast-Charge Controllers
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(IV+ = 10mA, TA= TMIN to TMAX, unless otherwise noted. Refer to the Typical Operating Circuit. All measurements are with respect to
BATT-, not GND.)
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.
V+ to BATT- .................................................................-0.3V, +7V
BATT- to GND ........................................................................±1V
BATT+ to BATT-
Power Not Applied............................................................±20V
With Power Applied ................................The higher of ±20V or
±2V x (programmed cells)
DRV to GND ..............................................................-0.3V, +20V
FASTCHG to BATT- ...................................................-0.3V, +12V
All Other Pins to GND......................................-0.3V, (V+ + 0.3V)
V+ Current.........................................................................100mA
DRV Current. .....................................................................100mA
REF Current.........................................................................10mA
Continuous Power Dissipation (TA= +70°C)
Plastic DIP (derate 10.53mW/°C above +70°C............842mW
Narrow SO (derate 8.70mW/°C above +70°C .............696mW
CERDIP (derate 10.00mW/°C above +70°C ................800mW
Operating Temperature Ranges
MAX71_C_E .......................................................0°C to +70°C
MAX71_E_E .................................................... -40°C to +85°C
MAX71_MJE ................................................. -55°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
VDRV = 10V
V+ = 0V, BATT+ = 17V
PGM3 = BATT-
5mA < IV+ < 20mA
PGM3 = REF
PGM3 = open
PGM3 = V+
0V < TEMP < 2V, TEMP voltage rising
VLIMIT = V+
Per cell
PGM0 = PGM1 = BATT-, BATT+ = 30V
1.2V < VLIMIT < 2.5V, 5mA < IDRV < 20mA,
PGM0 = PGM1 = V+
0mA < IREF < 1mA
CONDITIONS
mA30DRV Sink Current
%-1.5 1.5
Battery-Voltage to Cell-Voltage
Divider Accuracy
%-15 15Timer Accuracy
mV
26.0 31.3 38.0
Trickle-Charge VSENSE 12.0 15.6 20.0
4.5 7.8 12.0
1.5 3.9 7.0
mV225 250 275Fast-Charge VSENSE
V1.6 1.65 1.7Internal Cell Voltage Limit
mV-30 30VLIMIT Accuracy
µA-1 1THI, TLO, TEMP, VLIMIT Input Bias Current
µA5BATT+ Leakage
mA5IV+ (Note 1)
V4.5 5.5V+ Voltage
mV-10 10THI, TLO Offset Voltage (Note 2)
V02THI, TLO, TEMP Input Range
V1.25 2.50External VLIMIT Input Range
V0.35 0.50Undervoltage Lockout
kΩ30BATT+ Resistance with Power On
µF0.5C1 Capacitance
nF5C2 Capacitance
V1.96 2.04REF Voltage
UNITSMIN TYP MAXPARAMETER
MAX712
MAX713 mV/tA
per cell
0
Voltage-Slope Sensitivity (Note 3) -2.5
MAX712/MAX713
Maxim Integrated
ELECTRICAL CHARACTERISTICS (continued)
(IV+ = 10mA, TA= TMIN to TMAX, unless otherwise noted. Refer to the Typical Operating Circuit. All measurements are with respect to
BATT-, not GND.)
Note 1: The MAX712/MAX713 are powered from the V+ pin. Since V+ shunt regulates to +5V, R1 must be small enough to allow at
least 5mA of current into the V+ pin.
Note 2: Offset voltage of THI and TLO comparators referred to TEMP.
Note 3: tAis the A/D sampling interval (Table 3).
Note 4: This specification can be violated when attempting to charge more or fewer cells than the number programmed. To ensure
proper voltage-slope fast-charge termination, the (maximum battery voltage) ÷ (number of cells programmed) must fall
within the A/D input range.
NiCd/NiMH Battery
Fast-Charge Controllers
Battery voltage ÷ number of cells programmed
VFASTCHG = 10V
VFASTCHG = 0.4V
CONDITIONS
V1.4 1.9A/D Input Range (Note 4)
µA10
FASTCHG High Current
mA2
FASTCHG Low Current
UNITSMIN TYP MAXPARAMETER
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
20
1k 100k 1M10k 10M
CURRENT-SENSE AMPLIFIER
FREQUENCY RESPONSE (with 15pF)
-20
FREQUENCY (Hz)
GAIN (dB)
PHASE (DEGREES)
-10
0
10
40
-120
-80
-40
0
C2 = 15pF
FASTCHG = 0V
VOUT
VIN
CURRENT-
SENSE
AMP
BATT-
BATT-
CC
GND
--
++
AV
Φ
MAX712/13
toc01
20
-10
-20
10 1k
CURRENT-SENSE AMPLIFIER
FREQUENCY RESPONSE (with 10nF)
0
10
40
-80
-120
-40
0
FREQUENCY (Hz)
GAIN (dB)
PHASE (DEGREES)
100 10k
C2 = 10nF
FASTCHG = 0V
AV
Φ
MAX712/13
toc02
100
0.1
1.95 1.97 2.01 2.05
CURRENT ERROR-AMPLIFIER
TRANSCONDUCTANCE
1
10
VOLTAGE ON CC PIN (V)
DRV PIN SINK CURRENT(mA)
1.99 2.03
FASTCHG = 0V, V+ = 5V
MAX712/13 toc03
5.8
4.8
060
SHUNT-REGULATOR VOLTAGE
vs. CURRENT
5.6
CURRENT INTO V+ PIN (mA)
V+ VOLTAGE (V)
30
5.2
5.0
10 20 50
5.4
4.0
4.4
4.2
4.6
40
DRV NOT SINKING CURRENT
DRV SINKING CURRENT
MAX712/13 toc04
1.0
060
ALPHA SENSORS PART No. 14A1002
STEINHART-HART INTERPOLATION
1.6
BATTERY TEMPERATURE(°C)
TEMP PIN VOLTAGE (V)
BATTERY THERMISTOR RESISTANCE (kΩ)
30
1.4
1.2
10 20 50
0.2
0.6
0.4
0.8
20
35
30
25
0
10
5
15
40
MAX712/13
toc05
MAX712/MAX713
Maxim Integrated
3
NiCd/NiMH Battery
Fast-Charge Controllers
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
90
MAX713
NiMH BATTERY CHARGING
CHARACTERISTICS AT C RATE
CHARGE TIME (MINUTES)
03060
V
T
MAX712/13
toc07
ΔV
ΔtCUTOFF
1.60
CELL VOLTAGE (V)
CELL TEMPERATURE (°C)
1.45
1.55
1.50
40
25
35
30
150
MAX713
NiMH BATTERY CHARGING
CHARACTERISTICS AT C/2 RATE
1.55
1.40
050
1.50
1.45
40
25
35
30
V
T
ΔV
ΔtCUTOFF
CHARGE TIME (MINUTES)
CELL VOLTAGE (V)
CELL TEMPERATURE (°C)
100
MAX712/13
toc09
1.40
0
MAX713
NiCd BATTERY-CHARGING
CHARACTERISTICS AT C/2 RATE
1.45
CHARGE TIME (MINUTES)
CELL VOLTAGE (V)
CELL TEMPERATURE (°C)
1.50
25
30
35
50 150100
ΔV
ΔtCUTOFF
V
T
MAX712/13
toc08
15 20
MAX713
CHARGING CHARACTERISTICS OF A
FULLY-CHARGED NiMH BATTERY
1.60
CHARGE TIME (MINUTES)
CELL VOLTAGE (V)
CELL TEMPERATURE (°C)
1.45
1.65
05
1.55
1.50
40
25
35
30
10
V
T
ΔV
ΔtCUTOFF
5 MINUTE REST
BETWEEN CHARGES
MAX712/13
toc10
1.45
0
MAX713
CHARGING CHARACTERISTICS OF A
FULLY CHARGED NiMH BATTERY
1.50
CHARGE TIME (MINUTES)
CELL VOLTAGE (V)
CELL TEMPERATURE (°C)
1.60
1.65
1.55
25
30
40
35
51510
5-HOUR REST
BETWEEN CHARGES
ΔV
ΔtCUTOFF
V
T
20
MAX712/13
toc11
90
MAX713
NiCd BATTERY CHARGING
CHARACTERISTICS AT C RATE
1.55
CHARGE TIME (MINUTES)
CELL VOLTAGE (V)
CELL TEMPERATURE (°C)
1.40
030
1.50
1.45
40
25
35
30
60
V
T
ΔV
ΔtCUTOFF
MAX712/13
toc06
MAX712/MAX713
Maxim Integrated
NiCd/NiMH Battery
Fast-Charge Controllers
Pin Description
Compensation input for constant current regulation loopCC11
Negative terminal of batteryBATT-12
System ground. The resistor placed between BATT- and GND monitors the current into the battery.GND13
Current sink for driving the external PNP current sourceDRV14
Shunt regulator. The voltage on V+ is regulated to +5V with respect to BATT-, and the shunt current
powers the MAX712/MAX713.
V+15
Trip point for the under-temperature comparator. If the MAX712/MAX713 power on with the voltage-on
TEMP less than TLO, fast charge is inhibited and will not start until TEMP rises above TLO.
TLO6
Sense input for temperature-dependent voltage from thermistors.TEMP7
Open-drain, fast-charge status output. While the MAX712/MAX713 fast charge the battery, FASTCHG
sinks current. When charge ends and trickle charge begins, FASTCHG stops sinking current.
FASTCHG
8
PGM2 and PGM3 set the maximum time allowed for fast charging. Timeouts from 33 minutes to 264
minutes can be set by connecting to any of V+, REF, or BATT-, or by leaving the pin unconnected
(Table 3). PGM3 also sets the fast-charge to trickle-charge current ratio (Table 5).
PGM2,
PGM3
9, 10
Trip point for the over-temperature comparator. If the voltage-on TEMP rises above THI, fast charge ends.THI5
PGM0 and PGM1 set the number of series cells to be charged. The number of cells can be set from
1 to 16 by connecting PGM0 and PGM1 to any of V+, REF, or BATT-, or by leaving the pin unconnected
(Table 2). For cell counts greater than 11, see the Linear-Mode, High Series Cell Count section.
Charging more or fewer cells than the number programmed may inhibit ΔV fast-charge termination.
PGM0,
PGM1
3, 4
PIN
Positive terminal of batteryBATT+2
Sets the maximum cell voltage. The battery terminal voltage (BATT+ - BATT-) will not exceed VLIMIT x
(number of cells). Do not allow VLIMIT to exceed 2.5V. Connect VLIMIT to VREF for normal operation.
VLIMIT1
FUNCTIONNAME
2V reference outputREF16
MAX712/MAX713
Maxim Integrated
5
NiCd/NiMH Battery
Fast-Charge Controllers
Getting Started
The MAX712/MAX713 are simple to use. A complete
linear-mode fast-charge circuit can be designed in a
few easy steps. A linear-mode design uses the fewest
components and supplies a load while charging.
1) Follow the battery manufacturer’s recommendations
on maximum charge currents and charge-termination
methods for the specific batteries in your application.
Table 1 provides general guidelines.
2) Decide on a charge rate (Tables 3 and 5). The slow-
est fast-charge rate for the MAX712/MAX713 is C/4,
because the maximum fast-charge timeout period is
264 minutes. A C/3 rate charges the battery in about
three hours. The current in mA required to charge at
this rate is calculated as follows:
IFAST = (capacity of battery in mAh)
–––––––––––––––––––––––
––
(charge time in hours)
Depending on the battery, charging efficiency can be
as low as 80%, so a C/3 fast charge could take 3 hours
and 45 minutes. This reflects the efficiency with which
electrical energy is converted to chemical energy within
the battery, and is not the same as the power-
conversion efficiency of the MAX712/MAX713.
3) Decide on the number of cells to be charged (Table 2).
If your battery stack exceeds 11 cells, see the Linear-
Mode High Series Cell Count section. Whenever
changing the number of cells to be charged, PGM0
and PGM1 must be adjusted accordingly. Attempting
to charge more or fewer cells than the number pro-
grammed can disable the voltage-slope fast-charge
termination circuitry. The internal ADC’s input volt-
age range is limited to between 1.4V and 1.9V (see
the Electrical Characteristics), and is equal to the
voltage across the battery divided by the number of
cells programmed (using PGM0 and PGM1, as in
Table 2). When the ADC’s input voltage falls out of
its specified range, the voltage-slope termination cir-
cuitry can be disabled.
4) Choose an external DC power source (e.g., wall
cube). Its minimum output voltage (including ripple)
must be greater than 6V and at least 1.5V higher
than the maximum battery voltage while charging.
This specification is critical because normal fast-
charge termination is ensured only if this require-
ment is maintained (see Powering the
MAX712/MAX713 section for more details).
5) For linear-mode designs, calculate the worst-case
power dissipation of the power PNP and diode (Q1
and D1 in the Typical Operating Circuit) in watts,
using the following formula:
PDPNP = (maximum wall-cube voltage under
load - minimum battery voltage) x (charge current
in amps)
6) Limit current into V+ to between 5mA and 20mA. For a
fixed or narrow-range input voltage, choose R1 in the
Typical Operation Circuit using the following formula:
R1 = (minimum wall-cube voltage - 5V)/5mA
7) Choose RSENSE using the following formula:
RSENSE = 0.25V/(IFAST)
8) Consult Tables 2 and 3 to set pin-straps before
applying power. For example, to fast charge at a
rate of C/2, set the timeout to between 1.5x or 2x the
charge period, three or four hours, respectively.
Table 1. Fast-Charge Termination Methods
Charge
Rate NiMH Batteries NiCd Batteries
ΔV/Δt and/or
temperature, MAX713
ΔV/Δt and
temperature,
MAX712 or MAX713
> 2C
2C to C/2
ΔV/Δt and/or
temperature,
MAX712 or MAX713
ΔV/Δt and/or
temperature, MAX713
ΔV/Δt and/or
temperature, MAX713
ΔV/Δt and/or
temperature, MAX712
< C/2
MAX712/MAX713
Maxim Integrated
NiCd/NiMH Battery
Fast-Charge Controllers
Table 2. Programming the Number
of Cells
Table 3. Programming the Maximum
Charge Time
CONTROL LOGIC
+5V SHUNT
REGULATOR
TIMER
PGM2 PGM3
V+
BATT-
BATT-
UNDER_VOLTAGE
BATT-
DRV
V+
REF
100kΩ
100kΩ
N
HOT
ΔV_DETECT
TIMED_OUT
BATT-
FASTCHG
GND
CC
BATT-
GND
CELL_VOLTAGE
INTERNAL IMPEDANCE OF PGM0–PGM3 PINS
FAST_CHARGE
POWER_ON_RESET
IN_REGULATION
VLIMIT
BATT+
PGM0
PGM1
PGM2
PGM3
PGMx
THI
TEMP
TLO
ΔV
DETECTION
TEMPERATURE
COMPARATORS
CURRENT
AND
VOLTAGE
REGULATOR
COLD
0.4V
MAX712
MAX713
Figure 1. Block Diagram
PGM1
CONNECTION
PGM0
CONNECTION
1V+ V+
NUMBER
OF CELLS
2Open V+
4BATT- V+
3REF V+
6Open Open
5V+ Open
8BATT- Open
7REF Open
10 Open REF
9V+ REF
12 BATT- REF
11 REF REF
14 Open BATT-
13 V+ BATT-
16 BATT- BATT-
15 REF BATT-
22 V+ REF
PGM3
CONN
PGM2
CONN
22 V+ Open
33 V+ BATT-
TIMEOUT
(min)
33 V+ V+
45 Open REF
45 Open Open
66 Open BATT-
66 Open V+
90 REF REF
90 REF Open
132 REF BATT-
132 REF V+
180 BATT- REF
180 BATT- Open
264 BATT- BATT-
264 BATT- V+
21
21
21
A/D
SAMPLING
INTERVAL
(s) (tA)
21
42
42
42
42
84
84
84
84
168
168
168
168
Enabled
Disabled
Enabled
VOLTAGE-
SLOPE
TERMINATION
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
MAX712/MAX713
Maxim Integrated
7
NiCd/NiMH Battery
Fast-Charge Controllers
Detailed Description
The MAX712/MAX713 fast charge NiMH or NiCd batter-
ies by forcing a constant current into the battery. The
MAX712/MAX713 are always in one of two states: fast
charge or trickle charge. During fast charge, the
current level is high; once full charge is detected, the
current reduces to trickle charge. The device monitors
three variables to determine when the battery reaches
full charge: voltage slope, battery temperature, and
charge time.
Figure 1 shows the block diagram for the MAX712/
MAX713. The timer, voltage-slope detection, and temper-
ature comparators are used to determine full charge
state. The voltage and current regulator controls output
voltage and current, and senses battery presence.
Figure 2 shows a typical charging scenario with batteries
already inserted before power is applied. At time 1, the
MAX712/MAX713 draw negligible power from the bat-
tery. When power is applied to DC IN (time 2), the
power-on reset circuit (see the POWER
-
_ON
-
_RESET sig-
nal in Figure 1) holds the MAX712/MAX713 in trickle
charge. Once POWER
-
_ON
-
_RESET goes high, the device
enters the fast-charge state (time 3) as long as the cell
voltage is above the undervoltage lockout (UVLO) volt-
age (0.4V per cell). Fast charging cannot start until (bat-
tery voltage)/(number of cells) exceeds 0.4V.
When the cell voltage slope becomes negative, fast
charge is terminated and the MAX712/MAX713 revert
to trickle-charge state (time 4). When power is removed
(time 5), the device draws negligible current from the
battery.
Figure 3 shows a typical charging event using tempera-
ture full-charge detection. In the case shown, the bat-
tery pack is too cold for fast charging (for instance,
brought in from a cold outside environment). During
time 2, the MAX712/MAX713 remain in trickle-charge
state. Once a safe temperature is reached (time 3), fast
charge starts. When the battery temperature exceeds
the limit set by THI, the MAX712/MAX713 revert to trick-
le charge (time 4).
0
A
mA
μA
1
0.4
TIME
VOLTAGE
CELL VOLTAGE (V)CURRENT INTO CELL
CELL TEMPERATURE
1.4
1.5
1.3
2453
1. NO POWER TO CHARGER
2. CELL VOLTAGE LESS THAN 0.4V
3. FAST CHARGE
4. TRICKLE CHARGE
5. CHARGER POWER REMOVED
TEMPERATURE
Figure 2. Typical Charging Using Voltage Slope
A
mA
μA
1
TIME
CELL TEMPERATURECURRENT INTO CELL
TLO
THI
243
1. NO POWER TO CHARGER
2. CELL TEMPERATURE TOO LOW
3. FAST CHARGE
4. TRICKLE CHARGE
Figure 3. Typical Charging Using Temperature
A
1.5
1.4
1.3
mA
μA
1
TIME
VREF = VLIMIT
CELL VOLTAGE (V)CURRENT INTO CELL
243
1. BATTERY NOT INSERTED
2. FAST CHARGE
3. TRICKLE CHARGE
4. BATTERY REMOVED
Figure 4. Typical Charging with Battery Insertion
MAX712/MAX713
Maxim Integrated
NiCd/NiMH Battery
Fast-Charge Controllers
The MAX712/MAX713 can be configured so that voltage
slope and/or battery temperature detects full charge.
Figure 4 shows a charging event in which a battery is
inserted into an already powered-up MAX712/MAX713.
During time 1, the charger’s output voltage is regulated
at the number of cells times VLIMIT. Upon insertion of
the battery (time 2), the MAX712/MAX713 detect cur-
rent flow into the battery and switch to fast-charge
state. Once full charge is detected, the device reverts
to trickle charge (time 3). If the battery is removed (time
4), the MAX712/MAX713 remain in trickle charge and
the output voltage is once again regulated as in time 1.
Powering the MAX712/MAX713
AC-to-DC wall-cube adapters typically consist of a trans-
former, a full-wave bridge rectifier, and a capacitor.
Figures 10–12 show the characteristics of three con-
sumer product wall cubes. All three exhibit substantial
120Hz output voltage ripple. When choosing an adapter
for use with the MAX712/MAX713, make sure the lowest
wall-cube voltage level during fast charge and full load is
at least 1.5V higher than the maximum battery voltage
while being fast charged. Typically, the voltage on the
battery pack is higher during a fast-charge cycle than
while in trickle charge or while supplying a load. The volt-
age across some battery packs may approach 1.9V/cell.
The 1.5V of overhead is needed to allow for worst-case
voltage drops across the pass transistor (Q1 of Typical
2N3904
D1Q1
V+ DRV
DC IN
R1
R2
MAX712
MAX713
Figure 5. DRV Pin Cascode Connection (for high DC IN voltage
or to reduce MAX712/MAX713 power dissipation in linear mode)
↑1 x
UNDER_VOLTAGE IINN__RREEGGUULLAATTIIOONN
0 x x
↑x x
PPOOWWEERR__OONN__RREESSEETT
↑x 1
↑0 0
↑x x
1 0 0
1 0 0
1 0 ↓
1↓0
1 0 0
1 0 0
1 x x
1 x x
1 0 ↑
1↑0
Table 4. MAX712/MAX713 Charge-State Transition Table†
x
CCOOLLDD
x
0
x
1
x
↓
1
1
1
↑
1
x
0
x
x
x
HHOOTT
x
x
x
1
0
1
1
1
1
1
↑
0
x
x
x
No change
RESULT*
Set trickle
No change
No change
Set fast
No change***
No change
No change
Set fast
Set fast
Set fast**
No change***
Trickle to fast transition inhibited
Trickle to fast transition inhibited
Set trickle
Set trickle
1 x x x ↓Set trickle
†Only two states exist: fast charge and trickle charge.
*Regardless of the status of the other logic lines, a timeout or a voltage-slope detection will set trickle charge.
** If the battery is cold at power-up, the first rising edge on COLD will trigger fast charge; however, a second rising edge will
have no effect.
***Batteries that are too hot when inserted (or when circuit is powered up) will not enter fast charge until they cool and power is recycled.
MAX712/MAX713
Maxim Integrated
9
NiCd/NiMH Battery
Fast-Charge Controllers
Operating Circuit), the diode (D1), and the sense
resistor (RSENSE). This minimum input voltage require-
ment is critical, because violating it can inhibit proper
termination of the fast-charge cycle. A safe rule of
thumb is to choose a source that has a minimum input
voltage = 1.5V + (1.9V x the maximum number of cells
to be charged). When the input voltage at DC IN drops
below the 1.5V + (1.9V x number of cells), the part
oscillates between fast charge and trickle charge and
might never completely terminate fast-charge.
The MAX712/MAX713 are inactive without the wall cube
attached, drawing 5µA (max) from the battery. Diode
D1 prevents current conduction into the DRV pin. When
the wall cube is connected, it charges C1 through R1
(see Typical Operating Circuit) or the current-limiting
diode (Figure 19). Once C1 charges to 5V, the internal
shunt regulator sinks current to regulate V+ to 5V, and
fast charge commences. The MAX712/MAX713 fast
charge until one of the three fast-charge terminating
conditions is triggered.
If DC IN exceeds 20V, add a cascode connection in
series with the DRV pin as shown in Figure 5 to prevent
exceeding DRV’s absolute maximum ratings.
Select the current-limiting component (R1 or D4) to
pass at least 5mA at the minimum DC IN voltage (see
step 6 in the Getting Started section). The maximum
current into V+ determines power dissipation in the
MAX712/MAX713.
maximum current into V+ =
(maximum DC IN voltage - 5V)/R1
power dissipation due to shunt regulator =
5V x (maximum current into V+)
Sink current into the DRV pin also causes power dissipa-
tion. Do not allow the total power dissipation to exceed
the specifications shown in the Absolute Maximum
Ratings.
Fast Charge
The MAX712/MAX713 enter the fast-charge state under
one of the following conditions:
1) Upon application of power (batteries already
installed), with battery current detection (i.e., GND
voltage is less than BATT- voltage), and TEMP
higher than TLO and less than THI and cell voltage
higher than the UVLO voltage.
2) Upon insertion of a battery, with TEMP higher than
TLO and lower than THI and cell voltage higher than
the UVLO voltage.
RSENSE sets the fast-charge current into the battery. In
fast charge, the voltage difference between the BATT-
and GND pins is regulated to 250mV. DRV current
increases its sink current if this voltage difference falls
below 250mV, and decreases its sink current if the volt-
age difference exceeds 250mV.
fast-charge current (IFAST) = 0.25V/RSENSE
Trickle Charge
Selecting a fast-charge current (IFAST) of C/2, C, 2C, or
4C ensures a C/16 trickle-charge current. Other fast-
charge rates can be used, but the trickle-charge
current will not be exactly C/16.
The MAX712/MAX713 internally set the trickle-charge
current by increasing the current amplifier gain (Figure
6), which adjusts the voltage across RSENSE (see
Trickle-Charge VSENSE in the Electrical Characteristics
table).
BATT-
X
V+
OPEN
REF
BATT-
1
0
0
0
0
8
512
256
128
64
CURRENT-SENSE AMPLIFIER
PGM3 FAST_CHARGE Av
1.25V
V+
DC IN
GND
DRV
GND
CC
BATT-
RSENSE
D1
REF
VLIMIT
CELL_VOLTAGE
BATT-
BATT-
IN_REGULATION
C2
Figure 6. Current and Voltage Regulator (linear mode)
MAX712/MAX713
10
Maxim Integrated
NiCd/NiMH Battery
Fast-Charge Controllers
Nonstandard Trickle-Charge
Current Example
Configuration:
Typical Operating Circuit
2 x Panasonic P-50AA 500mAh AA NiCd batteries
C/3 fast-charge rate
264-minute timeout
Negative voltage-slope cutoff enabled
Minimum DC IN voltage of 6V
Settings:
Use MAX713
PGM0 = V+, PGM1 = open, PGM2 = BATT-,
PGM3 = BATT-, RSENSE = 1.5Ω(fast-charge current,
IFAST = 167mA), R1 = (6V - 5V)/5mA = 200Ω
Since PGM3 = BATT-, the voltage on RSENSE is regulat-
ed to 31.3mV during trickle charge, and the current is
20.7mA. Thus the trickle current is actually C/25, not
C/16.
Further Reduction of Trickle-Charge
Current for NiMH Batteries
The trickle-charge current can be reduced to less than
C/16 using the circuit in Figure 7. In trickle charge,
some of the current will be shunted around the battery,
since Q2 is turned on. Select the value of R7 as follows:
R7 = (VBATT + 0.4V)/(lTRlCKLE - IBATT)
where VBATT = battery voltage when charged
ITRlCKLE = MAX712/MAX713 trickle-charge
current setting
IBATT = desired battery trickle-charge current
Regulation Loop
The regulation loop controls the output voltage between
the BATT+ and BATT- terminals and the current
through the battery via the voltage between BATT- and
GND. The sink current from DRV is reduced when the
output voltage exceeds the number of cells times
VLIMIT, or when the battery current exceeds the pro-
grammed charging current.
For a linear-mode circuit, this loop provides the following
functions:
1) When the charger is powered, the battery can be
removed without interrupting power to the load.
2) If the load is connected as shown in the Typical
Operating Circuit, the battery current is regulated
regardless of the load current (provided the input
power source can supply both).
Voltage Loop
The voltage loop sets the maximum output voltage
between BATT+ and BATT-. If VLIMIT is set to less than
2.5V, then:
Maximum BATT+ voltage (referred to BATT-) = VLIMIT x
(number of cells as determined by PGM0, PGM1)
VLIMIT should be set between 1.9V and 2.5V. If VLIMIT
is set below the maximum cell voltage, proper
termination of the fast-charge cycle might not occur.
Cell voltage can approach 1.9V/cell, under fast charge,
in some battery packs. Tie VLIMIT to VREF for normal
operation.
With the battery removed, the MAX712/MAX713 do not
provide constant current; they regulate BATT+ to the
maximum voltage as determined above.
OPEN 2C IFAST/32
FAST-CHARGE
RATE
TRICKLE-CHARGE
CURRENT (ITRICKLE)
V+ 4C IFAST/64
BATT- C/2 IFAST/8
PGM3
REF C IFAST/16
Table 5. Trickle-Charge Current
Determination from PGM3
FASTCHG
RSENSE
BATTERY
R7
Q2
10k
V+
10k
DRV
D1Q1
DC IN
GND
MAX712
MAX713
Figure 7. Reduction of Trickle Current for NiMH Batteries
(Linear Mode)
MAX712/MAX713
Maxim Integrated
11
NiCd/NiMH Battery
Fast-Charge Controllers
The voltage loop is stabilized by the output filter
capacitor. A large filter capacitor is required only if the
load is going to be supplied by the MAX712/MAX713 in
the absence of a battery. In this case, set COUT as:
COUT (in farads) = (50 x ILOAD)/(VOUT x BWVRL)
where BWVRL = loop bandwidth in Hz
(10,000 recommended)
COUT > 10µF
ILOAD = external load current in amps
VOUT = programmed output voltage
(VLIMIT x number of cells)
Current Loop
Figure 6 shows the current-regulation loop for a linear-
mode circuit. To ensure loop stability, make sure that
the bandwidth of the current regulation loop (BWCRL) is
lower than the pole frequency of transistor Q1 (fB). Set
BWCRL by selecting C2.
BWCRL in Hz = gm/C2, C2 in farads,
gm = 0.0018 Siemens
The pole frequency of the PNP pass transistor, Q1, can
be determined by assuming a single-pole current gain
response. Both fTand Boshould be specified on the
data sheet for the particular transistor used for Q1.
fBin Hz = fT/Bo, fTin Hz, Bo= DC current gain
Condition for Stability of Current-Regulation Loop:
BWCRL < fB
The MAX712/MAX713 dissipate power due to the cur-
rent-voltage product at DRV. Do not allow the power
dissipation to exceed the specifications shown in the
Absolute Maximum Ratings. DRV power dissipation can
be reduced by using the cascode connection shown in
Figure 5.
Power dissipation due to DRV sink current =
(current into DRV) x (voltage on DRV)
Voltage-Slope Cutoff
The MAX712/MAX713’s internal analog-to-digital con-
verter has 2.5mV of resolution. It determines if the bat-
tery voltage is rising, falling, or unchanging by
comparing the battery’s voltage at two different times.
After power-up, a time interval of tAranging from 21sec
to 168sec passes (see Table 3 and Figure 8), then a
battery voltage measurement is taken. It takes 5ms to
perform a measurement. After the first measurement is
complete, another tAinterval passes, and then a
second measurement is taken. The two measurements
are compared, and a decision whether to terminate
charge is made. If charge is not terminated, another full
two-measurement cycle is repeated until charge is
terminated. Note that each cycle has two tAintervals
and two voltage measurements.
The MAX712 terminates fast charge when a compari-
son shows that the battery voltage is unchanging. The
MAX713 terminates when a conversion shows the bat-
tery voltage has fallen by at least 2.5mV per cell. This is
the only difference between the MAX712 and MAX713.
Temperature Charge Cutoff
Figure 9a shows how the MAX712/MAX713 detect over-
and under-temperature battery conditions using negative
temperature coefficient thermistors. Use the same model
thermistor for T1 and T2 so that both have the same
nominal resistance. The voltage at TEMP is 1V (referred
to BATT-) when the battery is at ambient temperature.
The threshold chosen for THI sets the point at which
fast charging terminates. As soon as the voltage-on
TEMP rises above THI, fast charge ends, and does not
restart after TEMP falls below THI.
The threshold chosen for TLO determines the tem-
perature below which fast charging will be inhibited.
If TLO > TEMP when the MAX712/MAX713 start up, fast
charge will not start until TLO goes below TEMP.
The cold temperature charge inhibition can be disabled
by removing R5, T3, and the 0.022μF capacitor; and by
tying TLO to BATT-.
To disable the entire temperature comparator charge-
cutoff mechanism, remove T1, T2, T3, R3, R4, and R5,
and their associated capacitors, and connect THI to V+
and TLO to BATT-. Also, place a 68kQ resistor from
REF to TEMP, and a 22kΩresistor from BATT- to TEMP.
5
ms 5
ms 5
ms 5
ms 5
ms 5
ms
tAtAtAtAtAtA
INTERVAL
NOTE: SLOPE PROPORTIONAL TO VBATT
INTERVAL INTERVAL INTERVAL INTERVAL INTERVAL
NEGATIVE
RESIDUAL
POSITIVE RESIDUAL
ZERO
RESIDUAL
VOLTAGE
RISES
0t
ZERO
VOLTAGE
SLOPE
CUTOFF FOR MAX712
NEGATIVE
VOLTAGE
SLOPE
CUTOFF FOR MAX712
OR MAX713
COUNTS
Figure 8. Voltage Slope Detection
MAX712/MAX713
12
Maxim Integrated
NiCd/NiMH Battery
Fast-Charge Controllers
Some battery packs come with a temperature-detect-
ing thermistor connected to the battery pack’s negative
terminal. In this case, use the configuration shown in
Figure 9b. Thermistors T2 and T3 can be replaced by
standard resistors if absolute temperature charge cut-
off is acceptable. All resistance values in Figures 9a
and 9b should be chosen in the 10kΩto 500kΩrange.
__________Applications Information
Battery-Charging Examples
Figures 13 and 14 show the results of charging 3 AA,
1000mAh, NiMH batteries from Gold Peak (part no.
GP1000AAH, GP Batteries (619) 438-2202) at a 1A rate
using the MAX712 and MAX713, respectively. The
Typical Operating Circuit is used with Figure 9a’s
thermistor configuration .
DC IN = Sony AC-190 +9VDC at 800mA AC-DC adapter
PGM0 = V+, PGM1 = REF, PGM2 = REF, PGM3 = REF
R1 = 200Ω, R2 = 150Ω, RSENSE = 0.25Ω
C1 = 1µF, C2 = 0.01µF, C3 = 10µF, VLIMIT = REF
R3 = 10kΩ, R4 = 15kΩ
T1, T2 = part #14A1002 (Alpha Sensors: 858-549-4660) R5
omitted, T3 omitted, TLO = BATT-
0.022μF
0.022μF
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
1μF
TEMP
TLO
IN THERMAL
CONTACT WITH
BATTERY
AMBIENT
TEMPERATURE
AMBIENT
TEMPERATURE
T3
+2.0V
T2
T1
R3
R4
R5
HOT
REF
THI
BATT-
COLD
MAX712
MAX713
Figure 9a. Temperature Comparators
MAX712
MAX713
0.022μF
0.022μF
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.
1μF
TEMP
TLO
AMBIENT
TEMPERATURE
AMBIENT
TEMPERATURE
IN THERMAL
CONTACT WITH
BATTERY
T3
+2.0V
T1
T2
R4
R3R5
HOT
REF
THI
BATT-
COLD
Figure 9b. Alternative Temperature Comparator Configuration
11
6
0 200 600 1000
7
10
MAX712/713
OUTPUT VOLTAGE (V)
400 800
9
8120Hz RIPPLE
LOW PEAK
HIGH PEAK
LOAD CURRENT (mA)
Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic,
9VDC 800mA
MAX712/MAX713
Maxim Integrated
13
NiCd/NiMH Battery
Fast-Charge Controllers
Linear-Mode, High Series Cell Count
The absolute maximum voltage rating for the BATT+ pin
is higher when the MAX712/MAX713 are powered on. If
more than 11 cells are used in the battery, the BATT+
input voltage must be limited by external circuitry when
DC IN is not applied (Figure 15).
Efficiency During Discharge
The current-sense resistor, RSENSE, causes a small
efficiency loss during battery use. The efficiency loss is
significant only if RSENSE is much greater than the
battery stack’s internal resistance. The circuit in Figure
16 can be used to shunt the sense resistor whenever
power is removed from the charger.
Status Outputs
Figure 17 shows a circuit that can be used to indicate
charger status with logic levels. Figure 18 shows a
circuit that can be used to drive LEDs for power and
charger status.
11
6
5
0 200 600 1000
7
10
MAX712/713
OUTPUT VOLTAGE (V)
400 800
9
8
LOW PEAK
HIGH PEAK
120Hz
RIPPLE
LOAD CURRENT (mA)
Figure 11. Sony CD Player AC Adapter AC-96N Load
Characteristic, 9VDC 600mA
4.3
4.2
030 90
4.5
5.0
4.9
4.7
4.4
BATTERY VOLTAGE (V)
BATTERY TEMPERATURE (°C)
60
TIME (MINUTES)
4.8
4.6
ΔV
ΔtCUTOFF
26
24
30
40
38
34
28
36
32
V
T
MAX712/713
Figure 13. 3 NiMH Cells Charged with MAX712
10
8
0 200 600
12
18
MAX712/713
OUTPUT VOLTAGE (V)
400
LOAD CURRENT (mA)
800
16
14
HIGH PEAK
LOW PEAK
120Hz
RIPPLE
Figure 12. Panasonic Modem AC Adapter KX-A11 Load
Characteristic, 12VDC 500mA
4.3
4.2
030 90
4.5
5.0
4.9
4.7
4.4
MAX712/713
BATTERY VOLTAGE (V)
BATTERY TEMPERATURE (°C)
60
TIME (MINUTES)
4.8
4.6
26
24
30
40
38
34
28
36
32
ΔV
ΔtCUTOFF
V
T
Figure 14. NiMH Cells Charged with MAX713
MAX712/MAX713
14
Maxim Integrated
NiCd/NiMH Battery
Fast-Charge Controllers
Q1 D1
R2
150Ω
DC IN
33kΩ
Q2
500Ω
DRV
BATT+
TO
BATTERY
POSITIVE
TERMINAL
MAX712
MAX713
Figure 15. Cascoding to Accommodate High Cell Counts for
Linear-Mode Circuits
100kΩ
D1
V+
GND
RSENSE
>4 CELLS
LOW RON
LOGIC LEVEL
N-CHANNEL
POWER
MOSFET
*
*
MAX712
MAX713
100kΩ
Figure 16. Shunting RSENSE for Efficiency Improvement
VCC
OV = NO POWER
5V = POWER
OV = FAST
VCC = TRICKLE OR
NO POWER
MAX712
MAX713
V+
FASTCHG
10kΩ
Figure 17. Logic-Level Status Outputs
V+
R1
470ΩMIN
FASTCHG
DC IN
CHARGE POWER
FAST CHARGE
MAX712
MAX713
Figure 18. LED Connection for Status Outputs
MAX712/MAX713
Maxim Integrated
15
NiCd/NiMH Battery
Fast-Charge Controllers
Ordering Information (continued) ___________________Chip Topography
DRV
THI
TLO
PGM3
0.126
(3.200mm)
0.80"
(2.032mm)
TEMP FASTCHG PGM2
GND
BATT-
CC
BATT+ VLIMIT REF V+
PGM1
PGM0
TRANSISTOR COUNT: 2193
SUBSTRATE CONNECTED TO V+
*Contact factory for dice specifications.
**Contact factory for availability and processing to MIL-STD-883.
PART TEMP RANGE PIN-PACKAGE
MAX713CPE 0°C to +70°C 16 Plastic DIP
16 Narrow SO0°C to +70°CMAX713CSE
MAX713C/D 0°C to +70°C Dice*
16 Plastic DIP-40°C to +85°CMAX713EPE
MAX713ESE
MAX713MJE
-40°C to +85°C
-55°C to +125°C
16 Narrow SO
16 CERDIP**
Package Information
(For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages.)
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
16 Plastic DIP P16-1 21-0043
16 Narrow SO S16-1 21-0041
16 CERDIP J16-3 21-0045
MAX712/MAX713
16
Maxim Integrated
NiCd/NiMH Battery
Fast-Charge Controllers
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
6 12/08 Removed switch mode power control and added missing package
information
1, 5, 6, 9, 10, 12,
13, 14, 16, 17
17
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
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. The parametric values (min and max limits) shown in the Electrical
Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
© 2008 Maxim Integrated The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.
MAX712/MAX713