Datasheet MAX713MJE, MAX713CSE, MAX713EPE, MAX713CPE, MAX712EPE Datasheet (Maxim)

19-0100; Rev 3; 1/97

EVALUATION KIT MANUALS

FOLLOW DATA SHEET

NiCd/NiMH Battery

Fast-Charge Controllers

_______________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 convert­er, 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 16­pin DIP and SO packages. An external power PNP tran­sistor, blocking diode, three resistors, and three
capacitors are the only required external components.

For high-power charging requirements, the MAX712/
MAX713 can be configured as a switch-mode battery
charger that minimizes power dissipation. Two evaluation
kits are available: Order the MAX712EVKIT-DIP for quick
evaluation of the linear charger, and the MAX713EVKIT­SO to evaluate the switch-mode 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 or Switch-Mode Power Control
♦ 5µA Max Drain on Battery when Not Charging
♦ 5V Shunt Regulator Powers External Logic

______________Ordering Information

PART

MAX712CPE

MAX712CSE
MAX712C/D 0°C to +70°C
MAX712EPE
MAX712ESE
MAX712MJE -55°C to +125°C

Ordering Information continued at end of data sheet.

*

Contact factory for dice specifications.

**

Contact factory for availability and processing to MIL-STD-883.

TEMP. RANGE PIN-PACKAGE

0°C to +70°C
0°C to +70°C

-40°C to +85°C 16 Plastic DIP

-40°C to +85°C

16 Plastic DIP
16 Narrow SO
Dice*

16 Narrow SO
16 CERDIP**

__________Typical Operating Circuit

R2
150Ω

Q1

2N6109



DC IN

R1

C4

0.01µF

MAX712/MAX713

__________________Pin Configuration

TOP VIEW

VLIMIT

1

BATT+

2

PGM0

3

PGM1

THI

TLO

TEMP

FASTCHG

________________________________________________________________

MAX712

4

MAX713

5
6
7
8

DIP/SO

REF

16

V+

15

DRV

14

GND

13

BATT-

12
11

CC

10

PGM3
PGM2

9

WALL 

CUBE

C1
1µF

R3

68kΩ

10µF

SEE FIGURE 19 FOR SWITCH-MODE CHARGER CIRCUIT.

R4

22kΩ

THI

V+

VLIMIT
REF

TEMP

C2

0.01µF

DRV

BATT+

MAX712
MAX713

BATT- TLO GNDCC

Maxim Integrated Products

BATTERY

R

D1
1N4001

C3
10µF

SENSE

LOAD

1

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone]

NiCd/NiMH Battery
Fast-Charge Controllers

ABSOLUTE MAXIMUM RATINGS

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

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

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.

MAX712/MAX713

ELECTRICAL CHARACTERISTICS

(IV+= 10mA, TA= T
BATT-, not GND.)

Trickle-Charge VSENSE

Voltage-Slope Sensitivity (Note 3)

Battery-Voltage to Cell-Voltage
Divider Accuracy

MIN

to T

±2V x (programmed cells)

, unless otherwise noted. Refer to

MAX

5mA < IV+< 20mA

V+ = 0V, BATT+ = 17V
PGM0 = PGM1 = BATT-, BATT+ = 30V

0mA < I

REF

Per cell

0V < TEMP < 2V, TEMP voltage rising

1.2V < V
PGM0 = PGM1 = V+

V

PGM3 = V+
PGM3 = open
PGM3 = REF
PGM3 = BATT­MAX713
MAX712

V

LIMIT

DRV

LIMIT

= V+

= 10V

< 1mA

REF Current.........................................................................10mA

Continuous Power Dissipation (T

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, 10sec).............................+300°C

Typical Operating Circuit

CONDITIONS

< 2.5V, 5mA < I

DRV

< 20mA,

. All measurements are with respect to

= +70°C)

A

1.5 3.9 7.0

4.5 7.8 12.0

12.0 15.6 20.0

26.0 31.3 38.0

-2.5
0

UNITSMIN TYP MAXPARAMETER

mV/t

per cell

V4.5 5.5V+ Voltage

mA5IV+(Note 1)

µA5BATT+ Leakage
kΩ30BATT+ Resistance with Power On
µF0.5C1 Capacitance
nF5C2 Capacitance

V1.96 2.04REF Voltage
V0.35 0.50Undervoltage Lockout
V1.25 2.50External VLIMIT Input Range
V02THI, TLO, TEMP Input Range

mV-10 10THI, TLO Offset Voltage (Note 2)

µA-1 1THI, TLO, TEMP, VLIMIT Input Bias Current

mV-30 30VLIMIT Accuracy

V1.6 1.65 1.7Internal Cell Voltage Limit

mV225 250 275Fast-Charge VSENSE

mV

A

%-15 15Timer Accuracy
%-1.5 1.5

mA30DRV Sink Current

2 _______________________________________________________________________________________

NiCd/NiMH Battery

Fast-Charge Controllers

ELECTRICAL CHARACTERISTICS (continued)

(IV+ = 10mA, TA= T
BATT-, not GND.)

FASTCHG Low Current
FASTCHG High Current

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: t

is the A/D sampling interval (Table 3).

A

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.

MIN

to T

, unless otherwise noted. Refer to

MAX

V

FASTCHG

V

FASTCHG

Battery voltage ÷ number of cells programmed

CONDITIONS

= 0.4V
= 10V

Typical Operating Circuit

. All measurements are with respect to

UNITSMIN TYP MAXPARAMETER

mA2

µA10

V1.4 1.9A/D Input Range (Note 4)

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

20

10

0

GAIN (dB)

-10

-20



CURRENT-SENSE AMPLIFIER

FREQUENCY RESPONSE (with 15pF)

C2 = 15pF

FASTCHG = 0V

A

Φ

BATT-

+

V

IN

-

GND

1k

CURRENT-

SENSE 

AMP

FREQUENCY (Hz)

CC

BATT-

100k

V

OUT

+

-



1M10k 10M

40

MAX712/13 LOG1

0

V

-40

PHASE (DEGREES)

-80

-120

20



10

GAIN (dB)

-10

-20

CURRENT-SENSE AMPLIFIER

FREQUENCY RESPONSE (with 10nF)

0

Φ

10 1k

100 10k

FREQUENCY (Hz)

C2 = 10nF

FASTCHG = 0V

A

V

40

MAX712/13 LOG2

0



-40

PHASE (DEGREES)

-80

-120

MAX712/MAX713

CURRENT ERROR-AMPLIFIER

TRANSCONDUCTANCE

100

FASTCHG = 0V, V+ = 5V

10

1

DRV PIN SINK CURRENT(mA)

0.1

1.95 1.97 2.01 2.05

1.99 2.03

VOLTAGE ON CC PIN (V)

_______________________________________________________________________________________ 3

MAX712/13 LOG3

V+ VOLTAGE (V)

SHUNT-REGULATOR VOLTAGE

vs. CURRENT

5.8
DRV NOT SINKING CURRENT

5.6

5.4

5.2

5.0

4.8

4.6

4.4

4.2

4.0

10 20 50

060

DRV SINKING CURRENT

30

40

CURRENT INTO V+ PIN (mA)

MAX712/13 LOG4

ALPHA THERMISTOR PART No. 13A1002

STEINHART-HART INTERPOLATION

1.6

1.4

1.2

1.0

0.8

0.6

TEMP PIN VOLTAGE (V)

0.4

0.2
10 20 50

060

BATTERY TEMPERATURE(°C)

35
30

25

20

15

10

5

BATTERY THERMISTOR RESISTANCE (kΩ)

30

40

0

NiCd/NiMH Battery
Fast-Charge Controllers

____________________________Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

MAX713

NiCd BATTERY-CHARGING

CHARACTERISTICS AT C RATE

CHARACTERISTICS AT C RATE

MAX713

NiMH BATTERY-CHARGING

1.55

1.50

1.45

CELL VOLTAGE (V)

1.40

∆V

V

CUTOFF

∆t

T

MAX712/MAX713

0

CHARACTERISTICS AT C/2 RATE

1.50

1.45

CELL VOLTAGE (V)

1.40

30 9060

CHARGE TIME (MINUTES)

MAX713

NiCd BATTERY-CHARGING

∆V

CUTOFF

∆t

V

T

MAX712/713

40

35

30

25

MAX712/713

35

30

25

MAX712/713

1.60

1.55

1.50

CELL VOLTAGE (V)

CELL TEMPERATURE (°C)

1.45

0

30 9060

CHARGE TIME (MINUTES)

∆V

V

T

∆t

CUTOFF

40

35

30

CELL TEMPERATURE (°C)

25

MAX713

NiMH BATTERY-CHARGING

CHARACTERISTICS AT C/2 RATE

MAX712/713

1.55

1.50

1.45

CELL VOLTAGE (V)

CELL TEMPERATURE (°C)

1.40

∆V

CUTOFF

∆t

V

T

40

35

30

CELL TEMPERATURE (°C)

25

0

50 150100

CHARGE TIME (MINUTES)

MAX713

CHARGING CHARACTERISTICS OF A 



FULLY CHARGED NiMH BATTERY

1.65

1.60

1.55

1.50

CELL VOLTAGE (V)

1.45

V

T

0

CHARGE TIME (MINUTES)

BETWEEN CHARGES

∆V

5152010

5-MINUTE REST 

∆t

CUTOFF

MAX712/713

40

35

30

25

0

CHARGING CHARACTERISTICS OF A 

1.65

1.60

1.55

1.50

CELL TEMPERATURE (°C)

CELL VOLTAGE (V)

1.45

0



50 150100

CHARGE TIME (MINUTES)

MAX713

FULLY CHARGED NiMH BATTERY

V

∆V

CUTOFF

∆t

5-HOUR REST 

BETWEEN CHARGES

T

51510

CHARGE TIME (MINUTES)

4 _______________________________________________________________________________________

MAX712/713

40

35

30

CELL TEMPERATURE (°C)

25

20

NiCd/NiMH Battery

Fast-Charge Controllers

______________________________________________________________Pin Description

PIN

3, 4

8

9, 10

VLIMIT1

PGM0,

PGM1

TLO6

FASTCHG

PGM2,

PGM3

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. Tie VLIMIT to VREF for normal operation.

Positive terminal of batteryBATT+2
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 open (Table

2). For cell counts greater than 11, see the
or fewer cells than the number programmed may inhibit ∆V fast-charge termination.

Trip point for the over-temperature comparator. If the voltage-on TEMP rises above THI, fast charge ends.THI5
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.
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.
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 open (Table 3).
PGM3 also sets the fast-charge to trickle-charge current ratio (Table 5).

Compensation input for constant current regulation loopCC11

FUNCTIONNAME

Linear-Mode, High Series Cell Count

section. Charging more

MAX712/MAX713

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

V+15

Shunt regulator. The voltage on V+ is regulated to +5V with respect to BATT-, and the shunt current
powers the MAX712/MAX713.

2V reference outputREF16

_______________________________________________________________________________________ 5

NiCd/NiMH Battery
Fast-Charge Controllers

____________________Getting Started

The MAX712/MAX713 are simple to use. A complete
linear-mode or switch-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, while a switch-mode design may be neces­sary if lower heat dissipation is desired.

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.

Table 1. Fast-Charge Termination Methods

Charge

MAX712/MAX713

Rate

> 2C

2C to C/2

< C/2

2) Decide on a charge rate (Tables 3 and 5). The slow­est 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:

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 power­conversion 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

Mode High Series Cell Count

changing the number of cells to be charged, PGM0

NiMH Batteries NiCd Batteries

∆V/∆t and
temperature,
MAX712 or MAX713

∆V/∆t and/or
temperature,
MAX712 or MAX713

∆V/∆t and/or
temperature, MAX712

I

= (capacity of battery in mAh)

FAST

–––––––––––––––––––––––

(charge time in hours)

∆V/∆t and/or
temperature, MAX713

∆V/∆t and/or
temperature, MAX713

∆V/∆t and/or
temperature, MAX713

section. Whenever

––

Linear-

and PGM1 must be adjusted accordingly. Attempting
to charge more or fewer cells than the number pro­grammed can disable the voltage-slope fast-charge
termination circuitry. The internal ADC’s input volt­age range is limited to between 1.4V and 1.9V (see

Electrical Characteristics

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 cir­cuitry 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 (2V
for switch mode) than the maximum battery voltage
while charging. This specification is critical because
normal fast-charge termination is ensured only if this
requirement is maintained (see

MAX712/MAX713

5) For linear-mode designs, calculate the worst-case
power dissipation of the power PNP and diode (Q1
and D1 in the
using the following formula:

PD
load - minimum battery voltage) x (charge current
in amps)

If the maximum power dissipation is not tolerable for
your application, refer to the
use a switch-mode design (see

= (maximum wall-cube voltage under

PNP

Operation

and see the MAX713 EV kit manual).

6) For both linear and switch-mode designs, limit cur­rent into V+ to between 5mA and 20mA. For a fixed
or narrow-range input voltage, choose R1 in the

section for more details).

Typical Operating Circuit

in the

Applications Information

Typical Operation Circuit

R1 = (minimum wall-cube voltage - 5V) / 5mA

For designs requiring a large input voltage variation,
choose the current-limiting diode D4 in Figure 19.

7) Choose R

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.

using the following formula:

SENSE

RSENSE = 0.25V / (I

), and is equal to the

Powering the

) in watts,

Detailed Description

or

Switch-Mode

section,

using the following formula:

)

FAST

6 _______________________________________________________________________________________

NiCd/NiMH Battery

Fast-Charge Controllers

Table 2. Programming the Number
of Cells

Number
of Cells

1 V+ V+
2 Open V+
3 REF V+
4 BATT- V+
5 V+ Open
6 Open Open
7 REF Open
8 BATT- Open

9 V+ REF
10 Open REF
11 REF REF
12 BATT- REF
13 V+ BATT­14 Open BATT­15 REF BATT­16 BATT- BATT-

PGM1 Connection PGM0 Connection

Table 3. Programming the Maximum
Charge Time

Timeout

(min)

22 V+ Open
22 V+ REF
33 V+ V+
33 V+ BATT­45 Open Open
45 Open REF
66 Open V+
66 Open BATT­90 REF Open

90 REF REF
132 REF V+
132 REF BATT­180 BATT- Open
180 BATT- REF
264 BATT- V+
264 BATT- BATT-

A/D

Sampling

Interval

(sec) (tA)

21
21
21
21
42
42
42
42
84
84
84

84
168
168
168
168

Voltage-

Slope

Termination

Disabled

Enabled

Disabled

Enabled

Disabled

Enabled

Disabled

Enabled

Disabled

Enabled

Disabled

Enabled

Disabled

Enabled

Disabled

Enabled

PGM3

Connection

Connection

MAX712/MAX713

PGM2

PGM2 PGM3

TIMER

PGM2

PGM3

THI

TEMP

TLO

∆V

DETECTION

TEMPERATURE

COMPARATORS

Figure 1. Block Diagram

_______________________________________________________________________________________ 7

TIMED_OUT

∆V_DETECT

HOT
COLD

V+

BATT-

CONTROL LOGIC

MAX712
MAX713

+5V SHUNT

REGULATOR

POWER_ON_RESET

FAST_CHARGE

IN_REGULATION

UNDER_VOLTAGE

CELL_VOLTAGE

0.4V
BATT-

GND

N

BATT-

CURRENT

AND

VOLTAGE

REGULATOR

BATT-

FASTCHG

DRV
CC

BATT­GND

VLIMIT
BATT+

PGM0
PGM1

INTERNAL IMPEDANCE OF PGM0–PGM3 PINS

PGMx

100k

100k

V+

REF

NiCd/NiMH Battery
Fast-Charge Controllers

_______________Detailed Description

The MAX712/MAX713 fast charge NiMH or NiCd batter­ies 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.

1.5

1.4

MAX712/MAX713

1. NO POWER TO CHARGER

2. CELL VOLTAGE LESS THAN 0.4V

3. FAST CHARGE

4. TRICKLE CHARGE

5. CHARGER POWER REMOVED

1.3

0.4

CELL VOLTAGE (V)CURRENT INTO CELL

0

A

mA

µA

Figure 2. Typical Charging Using Voltage Slope

VOLTAGE

TEMPERATURE

1

2



TIME





4

53

Figure 1 shows the block diagram for the MAX712/
MAX713. The timer, voltage-slope detection, and temper­ature 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 bat­tery. When power is applied to DC IN (time 2), the
power-on reset circuit (see the POWER
nal in Figure 1) holds the MAX712/MAX713 in trickle
charge. Once POWER
enters the fast-charge state (time 3) as long as the cell
voltage is above the undervoltage lockout (UVLO) volt­age (0.4V per cell). Fast charging cannot start until (bat­tery voltage) / (number of cells) exceeds 0.4V.

When the cell voltage slope becomes negative, fast

CELL TEMPERATURE

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 tempera­ture full-charge detection. In the case shown, the bat­tery 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 trick­le charge (time 4).

-

-

_ON

_RESET sig-

-

-

_ON

_RESET goes high, the device

VREF = VLIMIT

THI



TLO

CELL TEMPERATURECURRENT INTO CELL

A

mA

µA

1

1. NO POWER TO CHARGER

2. CELL TEMPERATURE TOO LOW

3. FAST CHARGE

4. TRICKLE CHARGE

243



TIME



Figure 3. Typical Charging Using Temperature

8 _______________________________________________________________________________________

1. BATTERY NOT INSERTED

2. FAST CHARGE

3. TRICKLE CHARGE

4. BATTERY REMOVED

Figure 4. Typical Charging with Battery Insertion

1.5


1.4

1.3

CELL VOLTAGE (V)CURRENT INTO CELL

A

mA

µA

1





243



TIME

NiCd/NiMH Battery

IN_REGULATION

POWER_ON_RESET

COLD

HOT

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.

the voltage on the battery pack is higher during a fast­charge cycle than while in trickle charge or while supply­ing a load. The voltage across some battery packs may
approach 1.9V/cell.

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 cur­rent flow into the battery and switch to fast-charge

DC IN

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 trans­former, a full-wave bridge rectifier, and a capacitor.
Figures 10–12 show the characteristics of three con­sumer 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 (2V for switch mode) than the maxi­mum battery voltage while being fast charged. Typically,

Figure 5. DRV Pin Cascode Connection (for high DC IN voltage
or to reduce MAX712/MAX713 power dissipation in linear mode)

Table 4. MAX712/MAX713 Charge-State Transition Table

UNDER_VOLTAGE

0 x x

↑
↑
↑
↑
↑

1 0 0
1 0 0
1
1 0
1 0 0
1 0 0
1 x x
1 x x
1
1 0
1 x x x

1 x
x 1
x x
x x
0 0

↓

↑

0

↓

0

↑

x
x
x

0

x
1
1

↓

1
1
1

↑

0

x

x

x

R2

R1

V+ DRV

MAX712
MAX713

†

x
x
x

x
0
1
1
1
1
1

↑

1
x
0
x
x

↓

Set trickle
No change
No change
No change
No change***
Set fast
No change
No change
Set fast
Set fast
No change***
Set fast**
Trickle to fast transition inhibited
Trickle to fast transition inhibited
Set trickle
Set trickle
Set trickle

MAX712/MAX713

D1Q1

2N3904

Result*

†

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.

_______________________________________________________________________________________ 9

NiCd/NiMH Battery
Fast-Charge Controllers

DC IN

DRV

D1

MAX712/MAX713

BATT-

R

SENSE

GND

Figure 6. Current and Voltage Regulator (linear mode)

The 1.5V of overhead is needed to allow for worst-case
voltage drops across the pass transistor (Q1 of

Operating Circuit

resistor (R
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

(Figure 19). Once C1 charges to 5V, the internal shunt

SENSE

V+

REF

VLIMIT

GND

CURRENT-SENSE AMPLIFIER

PGM3 FAST_CHARGE Av

OPEN

BATT-

V+

REF



1

X

0
0
0
0

CELL_VOLTAGE

8
512
256
128

64

BATT-

IN_REGULATION

1.25V
BATT-

), the diode (D1), and the sense

). This minimum input voltage require-

) or the current-limiting diode

Typical

CC

BATT-

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.
Furthermore, if Figure 19’s DC IN exceeds 15V, a tran­sistor level-shifter is needed to provide the proper volt­age swing to the MOSFET gate. See the MAX713 EV kit
manual for details.

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 =

C2

5V x (maximum current into V+)

Sink current into the DRV pin also causes power dissipa­tion. Do not allow the total power dissipation to exceed
the specifications shown in the

Ratings

.

Absolute Maximum

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.

R

sets the fast-charge current into the battery. In

SENSE

fast charge, the voltage difference between the BATT­and 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 volt­age difference exceeds 250mV.

fast-charge current (I

) = 0.25V / R

FAST

SENSE

Trickle Charge

Selecting a fast-charge current (I
4C ensures a C/16 trickle-charge current. Other fast­charge rates can be used, but the trickle-charge
current will not be exactly C/16.

) of C/2, C, 2C, or

FAST

10 ______________________________________________________________________________________

NiCd/NiMH Battery

Fast-Charge Controllers

Table 5. Trickle-Charge Current
Determination from PGM3

PGM3

V+ 4C I

OPEN 2C I

REF C I

BATT- C/2 I

Fast-Charge Rate

The MAX712/MAX713 internally set the trickle-charge
current by increasing the current amplifier gain (Figure

6), which adjusts the voltage across R
Trickle-Charge V

SENSE

in the

Electrical Characteristics

table).

Nonstandard Trickle-Charge

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-, R
I

= 167mA), R1 = (6V - 5V) / 5mA = 200Ω

FAST

= 1.5Ω (fast-charge current,

SENSE

Since PGM3 = BATT-, the voltage on R
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 = (V

where V

BATT

I

TRlCKLE

current setting
I

BATT

+ 0.4V) / (l

BATT

TRlCKLE

= battery voltage when charged

= MAX712/MAX713 trickle-charge

= desired battery trickle-charge current

Trickle-Charge

Current (I

FAST
FAST
FAST

FAST

TRICKLE

SENSE

)

/64
/32
/16

/8

(see

Current Example

is regulat-

SENSE

- I

)

BATT

DC IN

DRV

MAX712
MAX713

GND

Figure 7. Reduction of Trickle Current for NiMH Batteries
(linear mode)

FASTCHG

V+

10k

10k

D1Q1

R7

BATTERY

Q2

R

SENSE

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
V

, or when the battery current exceeds the pro-

LIMIT

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

Operating Circuit

, the battery current is regulated

Typical

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 V

2.5V, then:
Maximum BATT+ voltage (referred to BATT-) = V

(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 V

LIMIT

operation .
With the battery removed, the MAX712/MAX713 do not

provide constant current; they regulate BATT+ to the
maximum voltage as determined above.

is set to less than

LIMIT

to V

REF

LIMIT

for normal

x

MAX712/MAX713

______________________________________________________________________________________ 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 C

C

OUT

where BW

(in farads) = (50 x I

= loop bandwidth in Hz

VRL

LOAD

) / (V

OUT

OUT

x BW

VRL

(10,000 recommended)

C

> 10µF

OUT

I

= external load current in amps

LOAD

V

= programmed output voltage

OUT

(V

x number of cells)

LIMIT

Current Loop

Figure 6 shows the current-regulation loop for a linear­mode circuit. To ensure loop stability, make sure that

MAX712/MAX713

the bandwidth of the current regulation loop (BW
lower than the pole frequency of transistor Q1 (fB). Set
BW

by selecting C2.

CRL

BW

CRL

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:

BW

CRL

< f

B

The MAX712/MAX713 dissipate power due to the cur­rent-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 or by using a switch-mode circuit.

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 con­verter has 2.5mV of resolution. It determines if the bat­tery 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

as:

CRL

terminated. Note that each cycle has two tAintervals
and two voltage measurements.

The MAX712 terminates fast charge when a compari­son shows that the battery voltage is unchanging. The

)

MAX713 terminates when a conversion shows the bat­tery 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 over­and 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

) is

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 tem­perature 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 charge­cutoff 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.

Some battery packs come with a temperature-detecting
thermistor connected to the battery pack’s negative

ZERO

VOLTAGE

COUNTS

Figure 8. Voltage Slope Detection

VOLTAGE

RISES

0t

5ms 5ms 5ms 5ms 5ms 5ms

t

INTERVAL
NOTE: SLOPE PROPORTIONAL TO VBATT

t

A

A

INTERVAL INTERVAL INTERVAL INTERVAL INTERVAL

SLOPE

CUTOFF FOR MAX712

POSITIVE
RESIDUAL

t

t

A

A

NEGATIVE

VOLTAGE

SLOPE

CUTOFF FOR MAX712

OR MAX713

ZERO

RESIDUAL

t

A

t

A

NEGATIVE
RESIDUAL

12 ______________________________________________________________________________________

NiCd/NiMH Battery

Fast-Charge Controllers

IN THERMAL

CONTACT WITH

TEMPERATURE

R5

BATTERY

AMBIENT

T3

0.022µF

REF

R3

THI

HOT

R4

+2.0V

TEMP

COLD

TLO

0.022µF

MAX712
MAX713

BATT-

AMBIENT

TEMPERATURE

NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.

Figure 9a. Temperature Comparators

AMBIENT

REF

TEMPERATURE

terminal. In this case, use the configuration shown in

MAX712/MAX713

Figure 9b. Thermistors T2 and T3 can be replaced by
standard resistors if absolute temperature charge cut­off is acceptable. All resistance values in Figures 9a
and 9b should be chosen in the 10kΩto 500kΩrange.

T1

__________Applications Information

Switch-Mode Operation

For applications where the power dissipation in the
pass transistor cannot be tolerated (ie., where heat
sinking is not feasible or is too costly), a switch-mode

T2

1µF

charger is recommended.
Switch-mode operation can be implemented simply by

using the circuit of Figure 19. The circuit of Figure 19
uses the error amplifier at the CC pin as a comparator
with the 33pF capacitor adding hysteresis. Figure 19 is
shown configured to charge two cells at 1A. Lower
charge currents and a different number of cells can be
accommodated simply by changing R

SENSE

and

PGM0–PGM3 connections (Tables 2 and 3).
The input power-supply voltage range is 8V to 15V and

must be at least 2V greater than the peak battery
voltage, under fast charge. As shown in Figure 19, the
source should be capable of greater than 1.3A of
output current. The source requirements are critical
because if violated, proper termination of the fast­charge cycle might not occur. For input voltages
greater than 15V, see the MAX713SWEVKIT data sheet.

T2

HOT

+2.0V

COLD

MAX712
MAX713

NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE
REPLACED BY STANDARD RESISTORS.

THI

TEMP

TLO

BATT-

0.022µF

0.022µF

T1

IN THERMAL

CONTACT WITH

BATTERY

R3R5

1µF

R4

T3

AMBIENT

TEMPERATURE

Figure 9b. Alternative Temperature Comparator Configuration

______________________________________________________________________________________ 13

11

MAX712/713

10

HIGH PEAK

9

8

OUTPUT VOLTAGE (V)

7

6

0 200 600 1000

400

LOAD CURRENT (mA)

120Hz RIPPLE

LOW PEAK

800



Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic,
9VDC 800mA

NiCd/NiMH Battery
Fast-Charge Controllers

The voltage-slope, fast-charge termination circuitry
might become disabled if attempting to charge a
different number of cells than the number programmed.

The switching frequency (nominally 30kHz) can be
decreased by increasing the value of the capacitor
connected between CC and BATT-. Make sure that
the two capacitors connected to the CC node are
placed as close as possible to the CC pin on the
MAX712/MAX713 and that their leads are of minimum
length. The CC node is a high-impedance point, so do
not route logic lines near the CC pin. The circuit of
Figure 19 cannot service a load while charging.

Order the MAX713SWEVKIT-SO for quick evaluation of
the MAX712/MAX713 in switch-mode operation. For
more information on switch-mode operation and
ordering information for external components, order the

MAX712/MAX713

MAX713EVKIT data sheet.

11

10

9

8

7

OUTPUT VOLTAGE (V)

6

5

0 200 600 1000

HIGH PEAK

LOW PEAK

400

LOAD CURRENT (mA)

120Hz 

RIPPLE

800

Figure 11. Sony CD Player AC Adapter AC-96N Load
Characteristic, 9VDC 600mA

MAX712/713

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 [phone]) at a 1A rate
using the MAX712 and MAX713, respectively. The

Typical Operating Circuit

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, R
C1 = 1µF, C2 = 0.01µF, C3 = 10µF, V
R3 = 10kΩ, R4 = 15kΩ
T1, T2 = part #13A1002 (Alpha Thermistor: [phone])
R5 omitted, T3 omitted, TLO = BATT-



18

16

14

12

OUTPUT VOLTAGE (V)

10

8

Figure 12. Panasonic Modem AC Adapter KX-A11 Load
Characteristic, 12VDC 500mA

LOW PEAK

0 200 600

LOAD CURRENT (mA)

is used with Figure 9a’s

= 0.25Ω

SENSE

120Hz 

RIPPLE

400



HIGH PEAK

LIMIT

= REF

800

MAX712/713



5.0

4.9

4.8

4.7

4.6

4.5

BATTERY VOLTAGE (V)

4.4

4.3

4.2
030 90

∆V

∆t

V

TIME (MINUTES)

CUTOFF

T

60

Figure 13. 3 NiMH Cells Charged with MAX712

40

MAX712/713

38
36
34
32
30
28

26

24



BATTERY TEMPERATURE (°C)

Figure 14. NiMH Cells Charged with MAX713



5.0

4.9

4.8

4.7

4.6

4.5

BATTERY VOLTAGE (V)

4.4

4.3

4.2
030 90

∆V

∆t

V

TIME (MINUTES)

CUTOFF

T

60

14 ______________________________________________________________________________________

40

MAX712/713

38
36
34
32
30
28
26
24



BATTERY TEMPERATURE (°C)

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, R
efficiency loss during battery use. The efficiency loss is

Q1

DC IN

R2

150Ω

500Ω

DRV

, causes a small

SENSE

D1

33k

Q2

TO 
BATTERY 
POSITIVE 

TERMINAL

significant only if R

SENSE

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.

OV = NO POWER
5V = POWER

V

CC





OV = FAST

= TRICKLE OR 

V

CC

NO POWER

MAX712

MAX712
MAX713

MAX713

V+

10k

FASTCHG

MAX712/MAX713

MAX712
MAX713

BATT+

Figure 15. Cascoding to Accommodate High Cell Counts for
Linear-Mode Circuits

D1

>4 CELLS

MAX712
MAX713

100k

V+

Figure 16. Shunting R

100k

*

GND

for Efficiency Improvement

SENSE

R

SENSE

LOW R

*

ON

LOGIC LEVEL
N-CHANNEL
POWER
MOSFET

Figure 17. Logic-Level Status Outputs

DC IN

R1

CHARGE POWER

V+



MAX712

470ΩMIN

MAX713

FAST CHARGE

FASTCHG

Figure 18. LED Connection for Status Outputs

______________________________________________________________________________________ 15

NiCd/NiMH Battery
Fast-Charge Controllers

DC IN

8V TO 15V



3

Q4

CMPTA06

MAX712/MAX713

1

2



REF

68k

22k

C1
1µF
10V

C5
10µF
50V

D4
CCLHM080
(8mA CURRENT-
LIMITING DIODE)

R6

Ω

R7

Ω

R5

5

15

3

4

9

10
16

1
7

C4

0.1µF

THI
V+

PGM0

PGM1

PGM2
PGM3
REF
VLIMIT
TEMP

C6
10µF
50V

R2

5.1k

14

DRV

MAX713

FASTCHG

1

1

8

Q1
CMPTA06

2

Q2
2N2907

3

11

CC

BATT+

BATT-

3

2

TLD

GND





M1

IRFR9024

2

12

6

13



L1

D03340

220µH

D2
MBRS340T3

C2
220pF

R3

Ω

0.25







MBRS340T3





D1

2 x 1000mA-Hr

NiCd CELLS

C3
10µF
50V



BATT +

BATT–



470

Ω

Figure 19. Simplest Switch-Mode Charger

16 ______________________________________________________________________________________

NiCd/NiMH Battery

Fast-Charge Controllers

_Ordering Information (continued) ___________________Chip Topography

PART

MAX713CPE

MAX713CSE
MAX713C/D 0°C to +70°C
MAX713EPE
MAX713ESE
MAX713MJE -55°C to +125°C

*

Contact factory for dice specifications.

**

Contact factory for availability and processing to MIL-STD-883.

TEMP. RANGE PIN-PACKAGE

0°C to +70°C
0°C to +70°C

-40°C to +85°C 16 Plastic DIP

-40°C to +85°C

16 Plastic DIP
16 Narrow SO
Dice*

16 Narrow SO
16 CERDIP**

PGM0

PGM1

TLO

BATT+ VLIMIT REF V+

DRV

GND

0.126

(3.200mm)

BATT-

THI

CC

PGM3

MAX712/MAX713

TEMP FASTCHG PGM2

0.80"

(2.032mm)

TRANSISTOR COUNT: 2193
SUBSTRATE CONNECTED TO V+

______________________________________________________________________________________ 17

NiCd/NiMH Battery
Fast-Charge Controllers

MAX712/MAX713

NOTES

18 ______________________________________________________________________________________