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19-2366; Rev 4; 4/02
MAX712 Linear-Mode Evaluation Kit
General Description
The linear-mode evaluation kit (EV kit) is a complete battery charger for nickel metal hydride (NiMH) and "fast-charge" nickel-cadmium (NiCd) cells. The number of cells, charging current, and maximum charging time are selected by setting DIP switches. The board is easily tailored for the optimum charging parameters of a variety of "fast-charge" batteries, and can be used with either the MAX712 or MAX713. The MAX712 EV kit automatically initiates the highcurrent, fast-charge cycle when batteries are installed into the holder. An LED indicates that the fast-charge sequence is in progress. Fast charge terminates when the maximum charging time has lapsed, or the circuit detects that full charge has been achieved, and/or if the temperature is beyond acceptable limits. Thermistors are provided for optionally monitoring the battery temperature. The fast-charge cycle can be inhibited if the battery is too cold, or terminated if the battery temperature rises beyond limits. The temperature thresholds are adjustable using potentiometers on the board. o Selectable Number of Cells (1 to 16) o Selectable Maximum Fast-Charging Timeout o Selectable Charging Current o Battery Temperature Monitoring Capabilities o Adjustable Temperature Limits o LED Indication of Fast-Charge Cycle o On-Board Battery Holder for 1 or 2 AA Cells o Voltage-Slope Fast-Charge Termination
Features
Evaluates: MAX712/MAX713
Ordering Information
PART MAX712EVKIT-DIP TEMP RANGE 0C to +70C BOARD TYPE Through-Hole
______________________________________________________________Component List
DESIGNATION C1, C3 C2, C7 C4 C5, C6 C7 D1 IC1 J1 LED1, LED2 Q1 R1 R3, R5 R4 R6, R7 R8 R9-R11 R12-R15 R16 QTY 2 2 1 2 1 1 1 1 2 1 1 2 1 2 1 3 4 1 DESCRIPTION 10F, 35V electrolytic capacitors 1.0F ceramic capacitors 0.01F ceramic capacitor 0.022F ceramic capacitors 0.01F ceramic capacitor 1N4001 diode MAX712CPE TR1-TR3 3-pin jumper header Red LEDs 2N6109 PNP power transistor 200, 5% resistor 470, 5% resistors 150, 5% resistor 10k multiturn potentiometers 20k multiturn potentiometer 1k, 5% resistors 1.0k, 5% 1/2W resistors 2.0, 5% 1/2W resistor 1 None None None None None None None None None 1 2 1 1 1 1 4 1 1 3 DESIGNATION R17 R18 R19 R20 SWA SWB QTY 1 1 1 1 1 1 DESCRIPTION 3.9, 5% 1/2W resistor 8.2, 5% 1/2W resistor 16, 5% 1/2W resistor 330, 5% 1/2W resistor 12-position DIP switch 8-position DIP switch 10k at +25C thermistors. Alpha Sensors 14A1002 NTC. Phone (858) 549-4660. 16-pin IC socket Battery holder for two AA cells 2-pin power connector 3-pin power connector Shunt for J1 4in x 4in" PC board Rubber feet MAX712/MAX713 data sheet MAX712/MAX713 EV kit manual
________________________________________________________________ Maxim Integrated Products
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MAX712 Linear-Mode Evaluation Kit Evaluates: MAX712/MAX713
___________________Quick Reference
The MAX712 evaluation kit (EV kit) is ready to charge two fast-charging AA NimH cells. The switches and voltages are set at the factory per Tables 5, 6, and 7. Simply connect a 7V, 1A supply to the VIN power connector and insert two discharged AA NimH cells. The power-indicating LED will light as soon as power is applied. The voltage across the battery terminals, BATT+ and BATT-, will be two times the voltage on the VLIMIT pin. When batteries are inserted into the holder, the MAX712/MAX713 start a fast-charge cycle and light the charge-indicator LED. The default battery current is set to 250mA during the fast-charge cycle. Battery voltage can be monitored by connecting a voltmeter across the BATT+ and BATT- terminals. The MAX712 EV kit can be used to evaluate the MAX713 for charging NiCd batteries by replacing the MAX712CPE (included in this kit) with a MAX713CPE. Note: The EV kit is intended for use with cells capable of the high currents needed for fast-charging cycles. The proper charging current and period will depend on the exact type of battery being charged. Be sure the kit is configured properly. Check the default values and switch settings before applying power to the board. Refer to Tables 6 and 7 for the default settings. To ensure the board is operating, verify Table 8's voltages after power is applied and without a battery inserted.
Input Source
The MAX712/MAX713 require an input 1.5V greater than the maximum charging voltage, with a 6V minimum. Because of Q1's power-dissipation limits, the EV kit operates ideally with the input voltage set to 7V. This allows charging currents up to 1A while dissipating less than 5W from Q1. Higher input voltages and charging currents can be used if Q1's power dissipation is reduced or a sufficient heat sink is attached to Q1. For input voltages greater than 11V, it may be necessary to change R1's value, which must allow greater than 5mA for the MAX712/MAX713 plus approximately 16mA for drive current to the LED indicators. See the Powering the MAX712/MAX713 section of the data sheet for more information about R1 selection. For the EV kit, the input source must be capable of handling the charging current plus 25mA. Connect the source to a 2-terminal connector on the board marked +VIN and GND. When choosing an adapter for use with the MAX712/ MAX713, make sure that 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 voltage 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), the diode (D1), and the sense resistor (RSENSE). This minimum input voltage requirement is critical, because its violation may 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 will oscillate between fast charge and trickle charge and may never completely terminate fast charge.
_______________Detailed Description
The MAX712 EV kit provides the regulated high currents used for recharging the increasingly popular "fast-charge" batteries. The kit is shipped ready to charge two AA NimH cells. Be sure the programmed current does not exceed the maximum charging current of the batteries to be charged. Tables 1-5 list the different user options available on the EV kit. Tables 6, 7, and 8 list the levels preset at the factory for the various charging parameters.
Battery Connection
The battery connects across the battery high (BATT+) and battery low (BATT-) pins of the MAX712/MAX713. The pins connect to the battery holder and the 3-pin terminal block on the board. The battery holder charges one or two AA cells, depending on J1's position. Jumper J1 should be placed across pins 2 and 3 for a single cell and across 1 and 2 for two cells. External batteries can be connected across the BATT+ and BATT- pins of the 3-pin output connector. The third terminal is connected to the input ground (GND). The GND pin is used when driving external loads while charging.
Choosing Between the MAX712 and the MAX713
The MAX712 is intended to charge only NiMH batteries because it uses a zero delta voltage full-charge detection scheme. The MAX713 can be used to charge either NiCd or NiMH batteries because its 2.5mV-per-cell resolution allows it to detect the very slight peak in the NiMH charge characteristic. Some NiMH batteries require three different current levels when charging: an initial high current, an intermediate topping-off current, and a low trickle current. Neither the MAX712 nor the MAX713 is intended to charge this type of NiMH battery.
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MAX712 Linear-Mode Evaluation Kit
When using external batteries, jumper J1 has no effect. Remove all batteries from holder before installing external batteries. age range is limited to between 1.4V and 1.9V and is equal to the voltage across the battery divided by the number of cells programmed. When the ADC's input voltage falls out of its specified range, the voltage-slope termination circuitry is disabled. The MAX712/MAX713 multiply the input voltage on the VLIMIT pin by the programmed number of cells to be charged. This becomes the maximum output voltage of the MAX712/MAX713. VLIMIT should be set between 1.9V and 2.5V. If VLIMIT is set below the maximum cell voltage, proper termination of fast-charge cycle may not occur. Cell voltage can approach 1.9V/cell, under fast charge, in some battery packs. Tie VLIMIT to VREF for normal operation. PGM2 and PGM3 are used in combination to select the maximum charging time (timeout) and the time interval between samples taken by the internal ADC. The fastcharge cycle terminates regardless of the battery level when the timeout period expires. Timeout intervals between 22 and 264 minutes can be selected. The interval between the ADC samples varies with the timeout selection. If the voltage-slope fast-charge termination circuitry is enabled, the readings are also compared to the previous reading. Fast charge ceases if the delta is not more positive than zero for the MAX712 or -2.5mV for the MAX713. PGM3 also sets the sense voltage for the trickle-charge phase. The inputs to the programming pins (PGM0-PGM3) are set with the 12-position DIP switch (SWA). For example, to connect PGM2 to BATT-, first open (OFF) S7, S8, and S9, then close (ON) S8.
Evaluates: MAX712/MAX713
Sense-Resistor Selection
The charging rate is determined by the value of the sense resistor connected between BATT- and GND. The 8-position DIP switch (SWB) can select several different values. For fast charge, the sense voltage is fixed at 250mV and the resistor value is selected for the desired current. The sense resistor also sets the trickle current. Choose RSENSE using the following formula: RSENSE = 0.25V/IFAST See the MAX712/MAX713 data sheet for complete information on setting the currents for fast (IFAST) and trickle charging.
Table 1. Switch-Selected Sense-Resistor Values
SWITCH 1 2 3 4 5 6 7 8 RESISTOR () 1.0 1.0 1.0 1.0 2.0 3.9 8.2 16.0
Note: A 330 resistor (R20) is paralleled across the sense resistor to prevent the open-sense line condition. An unused resistor position (R21) is also provided so the user can mount a selected value.
Table 2. Programming Pin Input Selection
INPUT Open REF BATTV+ PGM0 -- S1 S2 S3 PGM1 -- S4 S5 S6 PGM2 -- S7 S8 S9 PGM3 -- S10 S11 S12
Mode Selection
Four pins on the MAX712/MAX713 are used to select the number of cells, maximum charging time, and interval between battery voltage measurements. PGM0 and PGM1 are used in combination to indicate the number of cells in the battery. Whenever changing the number of cells to be charged, PGM0 and PGM1 need to be adjusted accordingly. Attempting to charge more or fewer cells than the number programmed may disable the voltage-slope fastcharge termination circuitry. The internal ADC's input volt-
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MAX712 Linear-Mode Evaluation Kit Evaluates: MAX712/MAX713
Using the Thermistors
Thermistors TR1 and TR2 detect when the battery temperature exceeds the ambient temperature. With two of the same type of thermistors, as long as the battery temperature is the same as the ambient temperature, the voltage at TEMP will be 1.0V. At +25C ambient temperature and +35C battery temperature, TR2 has 10k resistance and TR1 has 5.2k resistance (refer to the graph labeled "Alpha Sensors Part No. 14A1002" in the Typical Operating Characteristics of the MAX712/MAX713 data sheet); thus TEMP equals 1.3V. Fast charge terminates once TEMP exceeds THI. Adjust the voltage on THI to set the over-temperature trip point. Thermistor TR3 detects when the temperature is too cold to fast charge the battery. Before charging has started, TEMP will equal 1.0V since the battery temperature will be the same as ambient. At 0C, TR3 has 33k resistance. Setting R8 to 33k inhibits fast charging for temperatures below 0C, since TR3's resistance will be greater than 33k at temperatures below 0C and thus the voltage at TLO will be greater than 1.0V. If the MAX712/MAX713's temperature detection features are not used, do not forget to disable the temperature comparators by tying THI = V+ and TLO = BATT-. TEMP should be connected to a voltage divider consisting of a 68k resistor to VREF, and a 22k resistor to BATT-. Refer to the Typical Operating Circuit of the MAX712/ MAX713 data sheet.
Table 3. Programming the Timing Functions
TIMEOUT (min) Sample Interval (s) 21 21 21 21 42 42 42 42 84 84 84 84 168 168 168 168 SLOPE LIMIT PGM2 PGM3 CONNECTION CONNECTION SENSE VOLTAGE IN TRICKLE (mV) 4 4 4 4 8 8 8 8 16 16 16 16 32 32 32 32
S7, S5, S9
S10, S11, S12
22 22 33 33 45 45 66 66 90 90 132 132 180 180 264 264
Off On Off On Off On Off On Off On Off On Off On Off On
Open REF V+ BATTOpen REF V+ BATTOpen REF V+ BATTOpen REF V+ BATT-
V+ V+ V+ V+ Open Open Open Open REF REF REF REF BATTBATTBATTBATT-
-- S7 S9 S8 -- S7 S9 S8 -- S7 S9 S8 -- S7 S9 S8
S12 S12 S12 S12 -- -- -- -- S10 S10 S10 S10 S11 S11 S11 S11
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MAX712 Linear-Mode Evaluation Kit
Table 4. Programming the Number of Cells
NUMBER OF CELLS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 PGM0 CONN V+ V+ V+ V+ Open Open Open Open REF REF REF REF BATTBATTBATTBATTPGM1 CONN V+ Open REF BATTV+ Open REF BATTV+ Open REF BATTV+ Open REF BATTS1-S3 S3 S3 S3 S3 Open Open Open Open S1 S1 S1 S1 S2 S2 S2 S2 S4-S6 S6 -- S4 S5 S6 -- S4 S5 S6 -- S4 S5 S6 -- S4 S5
Evaluates: MAX712/MAX713
Table 7. Evaluation Board Switch Settings for Charging Two NiCd AA Cells (Preshipment Settings)
SWITCH A (SWA) ON SWITCHES (ALL OTHERS OFF) S3, - FUNCTION
PGM0 = V+, PGM1 = Open PGM2 = BATT-, PGM3 = BATT- SWITCH B (SWB) S1 JUMPER J1 J1
Indicates two cells 264min timeout, 168s ADC interval, slope limit on
S8, S11
RSENSE = 1.0
Fast-charge current = 250mA
1&2
Set for charging two AA batteries
Table 5. Trickle-Charge Sense-Voltage Selection
PGM3 V+ Open REF BATTS10-S12 S12 -- S10 S11 SENSE VOLTAGE (mV) 4 8 16 32
Table 8. Voltage Values
VOLTAGE VALUE VREF VLIMIT 2.00 2.00 FUNCTION Internal fixed reference voltage Sets maximum charging voltage; R6 is adjusted to set the level. Set VLIMIT to VREF for normal operation. High-temperature trip voltage. Fast charge ceases when the TEMP pin exceeds this voltage. R7 is adjusted to set the level. Low-temperature trip voltage. Fast charge will not start when the TEMP pin is below this voltage. R8 is adjusted to set the level. This voltage is 1/2 of VREF as long as the two thermistors, TR1 and TR2, are at the same temperature. A Typical Operating Characteristics graph in the MAX712/ MAX713 data sheet shows how this voltage will vary with battery temperature. TR1 must be in contact with the battery casing to sense the battery temperature.
VTHI
1.33
Table 6. Factory Settings Before Shipment
Number of Cells Timeout ADC Interval Fast-Charge Current Trickle-Charge Current Battery Temperature Rise Cutoff VLIMIT 2 264 min 168 s 250mA 32mA +15C 2.0V VTEMP 1.00 VTLO 0.66
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MAX712 Linear-Mode Evaluation Kit Evaluates: MAX712/MAX713
BATTERY R21 LOW USER SELECTION R18 8.2 R17 3.9 SWB R16 2 R15 1 R14 1 C2 1.0F R13 1 R12 1 R10 1k R11 1k VREF R2 1k VREF BATTBATT1 2 3 4 5 6 7 R19 16 8 R20 330 BATTERY HIGH GND
J1 BATTERY B
LED1 POWER LED
D1 1N4001
BATTERY A
123
C0 USER SELECTION
FAST CHARGE
SWA
10 4 1 2 3 5 6 7 8 9
11 C4 0.01F 11
12 R5 470 LED2 C3 10F
R3 470
MAX712 MAX713 GND 13
V+ 15
FAST CHG 8
12
10
2
R2 USER OPTION
Q1 2N6109
R4 150
C7 0.01F
14 DRV
VLIMIT
BATT+
BATT-
TEMP
PGM0
PGM3
16 REF
C7 1.0F
R1 200
R6 10k
SWA
4 PGMI
TLO
THI
1
5
6
7
3
PGM2 9
CC
TP2 TEMP
TR1 10k @+25C
C5 0.022F
TP1 VREF
C1 10F
R7 10k
R8 20k
C6 0.022F
TR2 10k T @+25C
VDD
T
VDD
Figure 1. MAX712 Linear-Mode EV Kit Schematic
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.
6 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
TR3 10k @+25C
VIN
T
GND

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