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General Description The MAX712 MAX713 fast charge Nickel Metal Hydride NiMH and Nickel Cadmium NiCd batteries from a DC source at least 5V higher than the maximum battery voltage to 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 5m A 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 pin DIP and SO packages An external power PNP tran sistor 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 MAX713EVKIT SO to evaluate the switch mode charger

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Description

_______________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 5m A 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. 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 MAX713EVKIT- SO to evaluate the switch-mode charger.

  • charge time

  • max712

  • fast-charge controllers

  • max713

  • trickle-charge vsense

  • nimh battery

  • external components

  • current


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Informations

Publié par
Ajouté le 18 juin 2012
Nombre de lectures 686
Langue English
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MAX712/MAX713
19-0100; Rev 3; 1/97
NiCd/NiMH Battery
Fast-Charge Controllers
_______________General Description ____________________________Features
The MAX712/MAX713 fast charge Nickel Metal Hydride Fast Charge NiMH or NiCd Batteries
(NiMH) and Nickel Cadmium (NiCd) batteries from a DC Voltage Slope, Temperature, and Timer
source at least 1.5V higher than the maximum battery Fast-Charge Cutoff
voltage. 1 to 16 series cells can be charged at rates up
Charge 1 to 16 Series Cells
to 4C. A voltage-slope detecting analog-to-digital convert-
Supply Battery’s Load while Charging (Linear Mode)er, timer, and temperature window comparator determine
charge completion. The MAX712/MAX713 are powered Fast Charge from C/4 to 4C Rate
by the DC source via an on-board +5V shunt regulator. C/16 Trickle-Charge Rate
They draw a maximum of 5 A from the battery when not
Automatically Switch from Fast to Trickle Chargecharging. A low-side current-sense resistor allows the
Linear or Switch-Mode Power Controlbattery charge current to be regulated while still
supplying power to the battery’s load. 5µA Max Drain on Battery when Not Charging
The MAX712 terminates fast charge by detecting zero 5V Shunt Regulator Powers External Logic
voltage slope, while the MAX713 uses a negative
voltage-slope detection scheme. Both parts come in 16- ______________Ordering Information
pin DIP and SO packages. An external power PNP tran-
PART TEMP. RANGE PIN-PACKAGEsistor, blocking diode, three resistors, and three
capacitors are the only required external components. MAX712CPE 0°C to +70°C 16 Plastic DIP
For high-power charging requirements, the MAX712/ MAX712CSE 16 Narrow SO
MAX713 can be configured as a switch-mode battery MAX712C/D 0°C to +70°C Dice*
charger that minimizes power dissipation. Two evaluation MAX712EPE -40°C to +85°C 16 Plastic DIP
kits are available: Order the MAX712EVKIT-DIP for quick
MAX712ESE 16 Narrow SO
evaluation of the linear charger, and the MAX713EVKIT-
MAX712MJE -55°C to +125°C 16 CERDIP**SO to evaluate the switch-mode charger.
Ordering Information continued at end of data sheet.
________________________Applications *Contact factory for dice specifications.
**Contact factory for availability and processing to MIL-STD-883.
Battery-Powered Equipment
Laptop, Notebook, and Palmtop Computers __________Typical Operating Circuit
Handy-Terminals
Q1
Cellular Phones DC IN
2N6109
Portable Consumer Products
C4 R2Portable Stereos
R1 0.01 F 150
Cordless Phones
DRVTHI__________________Pin Configuration WALL D1
1N4001CUBE
V+
TOP VIEW
C1 VLIMIT BATT+
REFVLIMIT 1 16 1 F REF
BATT+ 2 15 V+ C3
R3 MAX712 10 FBATTERYDRVPGM0 3 14 68k
MAX713
PGM1 4 MAX712 13 GND TEMP
MAX713
LOADTHI 5 12 BATT- R4
10 F CC BATT- TLO GND22k
11 CCTLO 6
TEMP 7 10 PGM3 C2
0.01 F RPGM2 SENSEFASTCHG 8 9
SEE FIGURE 19 FOR SWITCH-MODE CHARGER CIRCUIT.DIP/SO
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
''''W'mm'WWm'm'm'm'
EVALUATION KIT MANUALS
FOLLOW DATA SHEETNiCd/NiMH Battery
Fast-Charge Controllers
ABSOLUTE MAXIMUM RATINGS
V+ to BATT-.................................................................-0.3V, +7V REF Current.........................................................................10mA
BATT- to GND........................................................................±1V Continuous Power Dissipation (T = +70°C)A
BATT+ to BATT- Plastic DIP (derate 10.53mW/°C above +70°C............842mW
Power Not Applied............................................................±20V Narrow SO (derate 8.70mW/°C above +70°C .............696mW
With Power Applied................................The higher of ±20V or CERDIP (derate 10.00mW/°C above +70°C ................800mW
±2V x (programmed cells) Operating Temperature Ranges
DRV to GND ..............................................................-0.3V, +20V MAX71_C_E .......................................................0°C to +70°C
FASTCHG to BATT-...................................................-0.3V, +12V MAX71_E_E .................................................... -40°C to +85°C
All Other Pins to GND......................................-0.3V, (V+ + 0.3V) MAX71_MJE ................................................. -55°C to +125°C
V+ Current.........................................................................100mA Storage Temperature Range .............................-65°C to +150°C
DRV Current......................................................................100mA Lead Temperature (soldering, 10sec) .............................+300°C
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.
ELECTRICAL CHARACTERISTICS
(I = 10mA, T = T to T , unless otherwise noted. Refer to Typical Operating Circuit. All measurements are with respect toV+ A MIN MAX
BATT-, not GND.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
V+ Voltage 5mA < I < 20mA 4.5 5.5 VV+
I (Note 1) 5 mAV+
BATT+ Leakage V+ = 0V, BATT+ = 17V 5 µA
BATT+ Resistance with Power On PGM0 = PGM1 = BATT-, BATT+ = 30V 30 kΩ
C1 Capacitance 0.5 µF
C2 Capacitance 5 nF
REF Voltage 0mA < I < 1mA 1.96 2.04 VREF
Undervoltage Lockout Per cell 0.35 0.50 V
External VLIMIT Input Range 1.25 2.50 V
THI, TLO, TEMP Input Range 02 V
THI, TLO Offset Voltage (Note 2) 0V < TEMP < 2V, TEMP voltage rising -10 10 mV
THI, TLO, TEMP, VLIMIT Input Bias Current -1 1 µA
1.2V < V < 2.5V, 5mA < I < 20mA,LIMIT DRVVLIMIT Accuracy -30 30 mV
PGM0 = PGM1 = V+
Internal Cell Voltage Limit V = V+ 1.6 1.65 1.7 VLIMIT
Fast-Charge VSENSE 225 250 275 mV
PGM3 = V+ 1.5 3.9 7.0
PGM3 = open 4.5 7.8 12.0
Trickle-Charge VSENSE mV
PGM3 = REF 12.0 15.6 20.0
PGM3 = BATT- 26.0 31.3 38.0
MAX713 -2.5 mV/tAVoltage-Slope Sensitivity (Note 3)
per cellMAX712 0
Timer Accuracy -15 15 %
Battery-Voltage to Cell-Voltage
-1.5 1.5 %
Divider Accuracy
DRV Sink Current V = 10V 30 mADRV
2 _______________________________________________________________________________________
MAX712/MAX713MAX712/MAX713
NiCd/NiMH Battery
Fast-Charge Controllers
ELECTRICAL CHARACTERISTICS (continued)
(I + = 10mA, T = T to T , unless otherwise noted. Refer to Typical Operating Circuit. All measurements are with respect toV A MIN MAX
BATT-, not GND.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
FASTCHG Low Current V = 0.4V 2 mAFASTCHG High Current V = 10V 10 µAFASTCHG
A/D Input Range (Note 4) Battery voltage ÷ number of cells programmed 1.4 1.9 V
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.
__________________________________________Typical Operating Characteristics
(T = +25°C, unless otherwise noted.)A
CURRENT-SENSE AMPLIFIER CURRENT-SENSE AMPLIFIER
FREQUENCY RESPONSE (with 15pF) FREQUENCY RESPONSE (with 10nF)
20 40 20 40
C2 = 15pF C2 = 10nF
FASTCHG = 0V FASTCHG = 0V
010 10 0
AA VV
0 -40 0 -40
BATT- CC
-80-10 -10 -80
++ CURRENT-
V VIN SENSE OUT
- -AMP
GND BATT-
-120-20 -20 -120
1k 10k 100k 1M 10M 10 100 1k 10k
FREQUENCY (Hz) FREQUENCY (Hz)
CURRENT ERROR-AMPLIFIER SHUNT-REGULATOR VOLTAGE ALPHA THERMISTOR PART No. 13A1002
TRANSCONDUCTANCE STEINHART-HART INTERPOLATIONvs. CURRENT
100 5.8 1.6 35
FASTCHG = 0V, V+ = 5V DRV NOT SINKING CURRENT5.6 1.4 30
5.4
1.2 25
10 5.2
1.0 205.0 DRV SINKING CURRENT
4.8 0.8 15
1 4.6 0.6 10
4.4
0.4 5
4.2
0.1 0.2 04.0
1.95 1.97 1.99 2.01 2.03 2.05 0610 20 30 40 5000610 20 30 40 500
VOLTAGE ON CC PIN (V) BATTERY TEMPERATURE(?C)CURRENT INTO V+ PIN (mA)
_______________________________________________________________________________________ 3
FWF
DRV PIN SINK CURRENT(mA)
GAIN (dB)
MAX712/13 LOG3
V+ VOLTAGE (V)
MAX712/13 LOG1
PHASE (DEGREES)
GAIN (dB)
MAX712/13 LOG4
TEMP PIN VOLTAGE (V)
MAX712/13 LOG2
PHASE (DEGREES)
BATTERY THERMISTOR RESISTANCE (k )NiCd/NiMH Battery
Fast-Charge Controllers
____________________________Typical Operating Characteristics (continued)
(T = +25°C, unless otherwise noted.)A
MAX713MAX713
NiCd BATTERY-CHARGING NiMH BATTERY-CHARGING
CHARACTERISTICS AT C RATECHARACTERISTICS AT C RATE
1.601.55 40 40
1.551.50 V 35 V V 35V CUTOFF CUTOFF
t t
1.501.45 30 30
T
T
25 1.45 251.40
0 30 60 90 0 30 60 90
CHARGE TIME (MINUTES)CHARGE TIME (MINUTES)
MAX713MAX713
NiCd BATTERY-CHARGING NiMH BATTERY-CHARGING
CHARACTERISTICS AT C/2 RATE CHARACTERISTICS AT C/2 RATE
1.55 V 40V CUTOFF1.50 35CUTOFF t
t
1.50 35
V1.45 V 30
1.45 30
T T
251.40
1.40 25
0 50 100 150 0 50 100 150
CHARGE TIME (MINUTES)CHARGE TIME (MINUTES)
MAX713 MAX713
CHARGING CHARACTERISTICS OF A CHARGING CHARACTERISTICS OF A
FULLY CHARGED NiMH BATTERY FULLY CHARGED NiMH BATTERY
1.65 1.65
5-MINUTE REST
BETWEEN CHARGESV
V
1.60 40 1.60 40VV CUTOFFCUTOFF tt
1.55 35 1.55 35
5-HOUR REST
BETWEEN CHARGES
1.50 30 1.50 30
T
T
1.45 25 1.45 25
05110520 051105 20
CHARGE TIME (MINUTES) CHARGE TIME (MINUTES)
4 _______________________________________________________________________________________
DDDDDDDDDDDD
MAX712/MAX713
CELL VOLTAGE (V) CELL VOLTAGE (V)
CELL VOLTAGE (V)
MAX712/713 MAX712/713
MAX712/713
CELL TEMPERATURE (?C) CELL TEMPERATURE (?C) CELL TEMPERATURE (?C)
CELL VOLTAGE (V)
CELL VOLTAGE (V) CELL VOLTAGE (V)
MAX712/713 MAX712/713
MAX712/713
CELL TEMPERATURE (?C) CELL TEMPERATURE (?C)
CELL TEMPERATURE (?C)MAX712/MAX713
NiCd/NiMH Battery
Fast-Charge Controllers
______________________________________________________________Pin Description
PIN NAME FUNCTION
Sets the maximum cell voltage. The battery terminal voltage (BATT+ - BATT-) will not exceed VLIMIT x
1 VLIMIT
(number of cells). Do not allow VLIMIT to exceed 2.5V. Tie VLIMIT to VREF for normal operation.
2 BATT+ Positive terminal of battery
PGM0 and PGM1 set the number of series cells to be charged. The number of cells can be set from
PGM0, 1 to 16 by connecting PGM0 and PGM1 to any of V+, REF, or BATT-, or by leaving the pin open (Table
3, 4
PGM1 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.
5 THI Trip point for the over-temperature comparator. If the voltage-on TEMP rises above THI, fast charge ends.
Trip point for the under-temperature comparator. If the MAX712/MAX713 power on with the voltage-on
6 TLO
TEMP less than TLO, fast charge is inhibited and will not start until TEMP rises above TLO.
7 TEMP Sense input for temperature-dependent voltage from thermistors.
Open-drain, fast-charge status output. While the MAX712/MAX713 fast charge the battery, FASTCHG
8 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
PGM2,
9, 10 minutes can be set by connecting to any of V+, REF, or BATT-, or by leaving the pin open (Table 3).
PGM3
PGM3 also sets the fast-charge to trickle-charge current ratio (Table 5).
11 CC Compensation input for constant current regulation loop
12 BATT- Negative terminal of battery
13 GND System ground. The resistor placed between BATT- and GND monitors the current into the battery.
14 DRV Current sink for driving the external PNP current source
Shunt regulator. The voltage on V+ is regulated to +5V with respect to BATT-, and the shunt current
15 V+
powers the MAX712/MAX713.
16 REF 2V reference output
_______________________________________________________________________________________ 5NiCd/NiMH Battery
Fast-Charge Controllers
and PGM1 must be adjusted accordingly. Attempting____________________Getting Started
to charge more or fewer cells than the number pro-
The MAX712/MAX713 are simple to use. A complete
grammed can disable the voltage-slope fast-charge
linear-mode or switch-mode fast-charge circuit can be
termination circuitry. The internal ADC’s input volt-
designed in a few easy steps. A linear-mode design
age range is limited to between 1.4V and 1.9V (see
uses the fewest components and supplies a load while
the Electrical Characteristics), and is equal to the
charging, while a switch-mode design may be neces-
voltage across the battery divided by the number of
sary if lower heat dissipation is desired.
cells programmed (using PGM0 and PGM1, as in
1) Follow the battery manufacturer’s recommendations Table 2). When the ADC’s input voltage falls out of
on maximum charge currents and charge-termination its specified range, the voltage-slope termination cir-
methods for the specific batteries in your application. cuitry can be disabled.
Table 1 provides general guidelines.
4) Choose an external DC power source (e.g., wall
cube). Its minimum output voltage (including ripple)
Table 1. Fast-Charge Termination Methods must be greater than 6V and at least 1.5V higher (2V
for switch mode) than the maximum battery voltage
Charge
NiMH Batteries NiCd Batteries while charging. This specification is critical becauseRate
normal fast-charge termination is ensured only if this
ΔV/Δt and requirement is maintained (see Powering theΔV/Δt and/or
> 2C temperature, MAX712/MAX713 section for more details). temperature, MAX713
MAX712 or MAX713
5) For linear-mode designs, calculate the worst-case
ΔV/Δt and/or power dissipation of the power PNP and diode (Q1ΔV/Δt and/or
2C to C/2 temperature, and D1 in the Typical Operating Circuit) in watts,
using the following formula:
PD = (maximum wall-cube voltage under PNPΔV/Δt and/or ΔV/Δt and/or
< C/2 load - minimum battery voltage) x (charge current temperature, MAX712 temperature, MAX713
in amps)
If the maximum power dissipation is not tolerable for
2) Decide on a charge rate (Tables 3 and 5). The slow- your application, refer to the Detailed Description or
est fast-charge rate for the MAX712/MAX713 is C/4, use a switch-mode design (see Switch-Mode
because the maximum fast-charge timeout period is Operation in the Applications Information section,
264 minutes. A C/3 rate charges the battery in about and see the MAX713 EV kit manual).
three hours. The current in mA required to charge at
6) For both linear and switch-mode designs, limit cur-
this rate is calculated as follows:
rent into V+ to between 5mA and 20mA. For a fixed
I = (capacity of battery in mAh)FAST or narrow-range input voltage, choose R1 in the
––––––––––––––––––––––––– Typical Operation Circuit using the following formula: (charge time in hours)
R1 = (minimum wall-cube voltage - 5V) / 5mADepending on the battery, charging efficiency can be
as low as 80%, so a C/3 fast charge could take 3 hours For designs requiring a large input voltage variation,
and 45 minutes. This reflects the efficiency with which choose the current-limiting diode D4 in Figure 19.
electrical energy is converted to chemical energy within 7) Choose R using the following formula: SENSE
the battery, and is not the same as the power-
RSENSE = 0.25V / (I )FASTconversion efficiency of the MAX712/MAX713.
8) Consult Tables 2 and 3 to set pin-straps before3) Decide on the number of cells to be charged (Table 2).
applying power. For example, to fast charge at aIf your battery stack exceeds 11 cells, see the Linear-
rate of C/2, set the timeout to between 1.5x or 2x theMode High Series Cell Count section. Whenever
charge period, three or four hours, respectively. changing the number of cells to be charged, PGM0
6 _______________________________________________________________________________________
MAX712/MAX713MAX712/MAX713
NiCd/NiMH Battery
Fast-Charge Controllers
Table 2. Programming the Number Table 3. Programming the Maximum
of Cells Charge Time
Number A/D
PGM1 Connection PGM0 Connection Voltage-
of Cells Timeout Sampling PGM3 PGM2
Slope
(min) Interval Connection Connection
Termination1 V+ V+
(sec) (t )A
2 Open V+
22 21 Disabled V+ Open
3 REF V+
22 21 Enabled V+ REF
4 BATT- V+ 33 21 Disabled V+ V+
5 V+ Open 33 21 Enabled V+ BATT-
6 Open Open 45 42 Disabled Open Open
7 REF Open 45 42 Enabled Open REF
8 BATT- Open 66 42 Disabled Open V+
66 42 Enabled Open BATT-9 V+ REF
90 84 Disabled REF Open10 Open REF
90 84 Enabled REF REF11 REF REF
132 84 Disabled REF V+12 BATT- REF
132 84 Enabled REF BATT-13 V+ BATT-
180 168 Disabled BATT- Open
14 Open BATT-
180 168 Enabled BATT- REF
15 REF BATT-
264 168 Disabled BATT- V+
16 BATT- BATT-
264 168 Enabled BATT- BATT-
V+
+5V SHUNT
GND
REGULATOR
PGM2 PGM3
FASTCHG
TIMED_OUT NBATT-
POWER_ON_RESET
TIMER
BATT-
DRVFAST_CHARGE CURRENT
PGM2 CCV_DETECT ANDV CONTROL LOGIC V+
IN_REGULATION VOLTAGE BATT-DETECTION
PGM3 REGULATOR 100kGND
VLIMIT PGMx
BATT+UNDER_VOLTAGE
HOT
100kTHI
TEMPERATURE COLD
TEMP PGM0COMPARATORS REFTLO CELL_VOLTAGE
PGM1
MAX712
MAX713 0.4V
BATT-
INTERNAL IMPEDANCE OF PGM0–PGM3 PINSBATT-
Figure 1. Block Diagram
_______________________________________________________________________________________ 7
DDNiCd/NiMH Battery
Fast-Charge Controllers
Figure 1 shows the block diagram for the MAX712/_______________Detailed Description
MAX713. The timer, voltage-slope detection, and temper-
The MAX712/MAX713 fast charge NiMH or NiCd batter-
ature comparators are used to determine full charge
ies by forcing a constant current into the battery. The
state. The voltage and current regulator controls output
MAX712/MAX713 are always in one of two states: fast
voltage and current, and senses battery presence.
charge or trickle charge. During fast charge, the
Figure 2 shows a typical charging scenario with batteriescurrent level is high; once full charge is detected, the
already inserted before power is applied. At time 1, thecurrent reduces to trickle charge. The device monitors
MAX712/MAX713 draw negligible power from the bat-three variables to determine when the battery reaches
tery. When power is applied to DC IN (time 2), thefull charge: voltage slope, battery temperature, and - -
power-on reset circuit (see the POWER_ON_RESET sig-charge time.
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 cell1.5
voltage is above the undervoltage lockout (UVLO) volt-
1.4 age (0.4V per cell). Fast charging cannot start until (bat-VOLTAGE
tery voltage) / (number of cells) exceeds 0.4V. 1.3
TEMPERATURE
When the cell voltage slope becomes negative, fast
0.4
charge is terminated and the MAX712/MAX713 revert
0
to trickle-charge state (time 4). When power is removed
A (time 5), the device draws negligible current from the
battery.
Figure 3 shows a typical charging event using tempera-mA
ture full-charge detection. In the case shown, the bat-
A tery pack is too cold for fast charging (for instance,
1 2 3 4 5 brought in from a cold outside environment). During
1. NO POWER TO CHARGER TIME time 2, the MAX712/MAX713 remain in trickle-charge
2. CELL VOLTAGE LESS THAN 0.4V
state. Once a safe temperature is reached (time 3), fast3. FAST CHARGE
charge starts. When the battery temperature exceeds4. TRICKLE CHARGE
5. CHARGER POWER REMOVED the limit set by THI, the MAX712/MAX713 revert to trick-
le charge (time 4).
Figure 2. Typical Charging Using Voltage Slope
VREF = VLIMIT
THI
1.5
1.4
1.3TLO
A
A
mAmA
AA
1 2431243
1. BATTERY NOT INSERTED TIME1. NO POWER TO CHARGER TIME
2. FAST CHARGE2. CELL TEMPERATURE TOO LOW
3. TRICKLE CHARGE3. FAST CHARGE
4. BATTERY REMOVED4. TRICKLE CHARGE
Figure 3. Typical Charging Using Temperature Figure 4. Typical Charging with Battery Insertion
8 _______________________________________________________________________________________
mmm
MAX712/MAX713
CURRENT INTO CELL CELL TEMPERATURE CURRENT INTO CELL CELL VOLTAGE (V)
CELL TEMPERATURE
CURRENT INTO CELL CELL VOLTAGE (V)MAX712/MAX713
NiCd/NiMH Battery
Fast-Charge Controllers
The MAX712/MAX713 can be configured so that voltage the voltage on the battery pack is higher during a fast-
slope and/or battery temperature detects full charge. charge cycle than while in trickle charge or while supply-
ing a load. The voltage across some battery packs mayFigure 4 shows a charging event in which a battery is
approach 1.9V/cell.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-
Q1 D1
rent flow into the battery and switch to fast-charge DC IN
state. Once full charge is detected, the device reverts
R2to trickle charge (time 3). If the battery is removed (time
4), the MAX712/MAX713 remain in trickle charge and R1
the output voltage is once again regulated as in time 1.
2N3904Powering the MAX712/MAX713
AC-to-DC wall-cube adapters typically consist of a trans-
former, a full-wave bridge rectifier, and a capacitor. V+ DRV
Figures 10–12 show the characteristics of three con-
sumer product wall cubes. All three exhibit substantial
MAX712
120Hz output voltage ripple. When choosing an adapter
MAX713
for use with the MAX712/MAX713, make sure the lowest
wall-cube voltage level during fast charge and full load is
Figure 5. DRV Pin Cascode Connection (for high DC IN voltageat least 1.5V higher (2V for switch mode) than the maxi-
or to reduce MAX712/MAX713 power dissipation in linear mode)mum battery voltage while being fast charged. Typically,
†Table 4. MAX712/MAX713 Charge-State Transition Table
UNDER_VOLTAGE Result*
0 x x x x Set trickle
1 x x x No change
x 1 x x
x x 0 x No change
x x x 0 No change***
0 0 1 1 Set fast
1 0 0 1 1 No change
1 0 0 1
1 0 1 1 Set fast
1 0 1 1
1 0 0 1 No change***
1 0 0 1 Set fast**
1 x x 0 x Trickle to fast transition inhibited
1 x x x 0
1 0 x x Set trickle
1 0 x x
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.
_______________________________________________________________________________________ 9
fl››››flfl›››››fl
HOT COLD IN_REGULATION POWER_ON_RESETNiCd/NiMH Battery
Fast-Charge Controllers
regulator sinks current to regulate V+ to 5V, and fast
DC IN charge commences. The MAX712/MAX713 fast charge
V+ 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
REF exceeding DRV’s absolute maximum ratings.
Furthermore, if Figure 19’s DC IN exceeds 15V, a tran-DRV
sistor level-shifter is needed to provide the proper volt-
VLIMIT
age swing to the MOSFET gate. See the MAX713 EV kit
manual for details.
D1 CELL_VOLTAGE Select the current-limiting component (R1 or D4) to
GND
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 theCURRENT-SENSE AMPLIFIER
MAX712/MAX713.
PGM3 FAST_CHARGE Av
maximum current into V+ =X 1 8
V+ 0 512 (maximum DC IN voltage - 5V) / R1
0 256OPEN
power dissipation due to shunt regulator =REF 0 128 CC
BATT- 0 64BATT- 5V x (maximum current into V+)C2
Sink current into the DRV pin also causes power dissipa-
tion. Do not allow the total power dissipation to exceedRSENSE BATT-BATT- the specifications shown in the Absolute Maximum
Ratings.
IN_REGULATION
GND Fast Charge1.25V
The MAX712/MAX713 enter the fast-charge state under
BATT-
one of the following conditions:
1) Upon application of power (batteries already
installed), with battery current detection (i.e., GND
Figure 6. Current and Voltage Regulator (linear mode) voltage is less than BATT- voltage), and TEMP
higher than TLO and less than THI and cell voltage
higher than the UVLO voltage.
The 1.5V of overhead is needed to allow for worst-case
2) Upon insertion of a battery, with TEMP higher thanvoltage drops across the pass transistor (Q1 of Typical
TLO and lower than THI and cell voltage higher thanOperating Circuit), the diode (D1), and the sense
the UVLO voltage. resistor (R ). This minimum input voltage require-SENSE
ment is critical, because violating it can inhibit proper R sets the fast-charge current into the battery. InSENSE
termination of the fast-charge cycle. A safe rule of fast charge, the voltage difference between the BATT-
thumb is to choose a source that has a minimum input and GND pins is regulated to 250mV. DRV current
voltage = 1.5V + (1.9V x the maximum number of cells increases its sink current if this voltage difference falls
to be charged). When the input voltage at DC IN drops below 250mV, and decreases its sink current if the volt-
below the 1.5V + (1.9V x number of cells), the part age difference exceeds 250mV.
oscillates between fast charge and trickle charge and
fast-charge current (I ) = 0.25V / RFAST SENSE
might never completely terminate fast-charge.
Trickle ChargeThe MAX712/MAX713 are inactive without the wall cube
Selecting a fast-charge current (I ) of C/2, C, 2C, orattached, drawing 5 A (max) from the battery. Diode D1 FAST
4C ensures a C/16 trickle-charge current. Other fast-prevents current conduction into the DRV pin. When the
charge rates can be used, but the trickle-charge wall cube is connected, it charges C1 through R1 (see
current will not be exactly C/16. Typical Operating Circuit) or the current-limiting diode
(Figure 19). Once C1 charges to 5V, the internal shunt
10 ______________________________________________________________________________________
m
MAX712/MAX713