For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
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 easi-
ly 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 high-
current, 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 bat-
tery temperature. The fast-charge cycle can be inhibited if
the battery is too cold, or terminated if the battery tempera-
ture rises beyond limits. The temperature thresholds are
adjustable using potentiometers on the board.
Features
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
Ordering Information
Evaluates: MAX712/MAX713
MAX712 Linear-Mode Evaluation Kit
________________________________________________________________ Maxim Integrated Products
1
______________________________________________________________Component List
PART
TEMP RANGE
BOARD TYPE
MAX712EVKIT-DIP
0C to +70C
Through-Hole
DESIGNATION
QTY
DESCRIPTION
C1, C3
2
10F, 35V electrolytic capacitors
2
1.0F ceramic capacitors
C4
1
0.01F ceramic capacitor
C5, C6
2
0.022F ceramic capacitors
D1
1
1N4001 diode
J1
1
3-pin jumper header
LED1, LED2
2
Red LEDs
C2, C7
Q1
1
2N6109 PNP power transistor
R1
1
200
, 5% resistor
R4
1
150
, 5% resistor
R6, R7
2
10k
multiturn potentiometers
R8
1
20k
multiturn potentiometer
R9R11
3
1k
, 5% resistors
R12R15
4
1.0k
, 5% 1/2W resistors
R16
1
2.0
, 5% 1/2W resistor
R3, R5
2
470
, 5% resistors
12-position DIP switch
1
SWA
330
, 5% 1/2W resistor
1
R20
8-position DIP switch
1
SWB
3.9
, 5% 1/2W resistor
1
R17
MAX712/MAX713 EV kit manual
1
None
MAX712/MAX713 data sheet
1
None
Rubber feet
4
None
4in x 4in" PC board
1
None
Shunt for J1
1
None
3-pin power connector
1
None
2-pin power connector
1
None
Battery holder for two AA cells
2
None
16-pin IC socket
1
None
10k
at +25C thermistors.
Alpha Sensors 14A1002 NTC.
Phone (858) 549-4660.
3
TR1TR3
DESCRIPTION
QTY
DESIGNATION
C7
1
0.01F ceramic capacitor
16
, 5% 1/2W resistor
1
R19
19-2366; Rev 4; 4/02
8.2
, 5% 1/2W resistor
1
R18
IC1
1
MAX712CPE
Evaluates: MAX712/MAX713
MAX712 Linear-Mode Evaluation Kit
2
_______________________________________________________________________________________
___________________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 con-
nect a 7V, 1A supply to the V
IN
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.
_______________Detailed Description
The MAX712 EV kit provides the regulated high cur-
rents 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 cur-
rent of the batteries to be charged. Tables 15 list the
different user options available on the EV kit. Tables 6,
7, and 8 list the levels preset at the factory for the vari-
ous charging parameters.
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 differ-
ent current levels when charging: an initial high current,
an intermediate topping-off current, and a low trickle cur-
rent. Neither the MAX712 nor the MAX713 is intended to
charge this type of NiMH battery.
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 oper-
ates 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 infor-
mation 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 high-
er 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 (R
SENSE
). 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 mini-
mum input voltage = 1.5V + (1.9V x the maximum num-
ber 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.
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 ter-
minal 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.
Evaluates: MAX712/MAX713
MAX712 Linear-Mode Evaluation Kit
_______________________________________________________________________________________
3
When using external batteries, jumper J1 has no
effect. Remove all batteries from holder before
installing external batteries.
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 dif-
ferent 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 R
SENSE
using the following formula:
R
SENSE
= 0.25V/I
FAST
See the MAX712/MAX713 data sheet for complete
information on setting the currents for fast (I
FAST
) and
trickle charging.
Table 1. Switch-Selected Sense-Resistor
Values
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.
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 num-
ber programmed may 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 and is
equal to the voltage across the battery divided by the
number of cells programmed. When the ADC's input volt-
age falls out of its specified range, the voltage-slope ter-
mination 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. V
LIMIT
should be set between 1.9V and
2.5V. If V
LIMIT
is set below the maximum cell voltage, prop-
er termination of fast-charge cycle may not occur. Cell volt-
age can approach 1.9V/cell, under fast charge, in some
battery packs. Tie V
LIMIT
to V
REF
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 fast-
charge 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 termi-
nation circuitry is enabled, the readings are also com-
pared 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.
Table 2. Programming Pin Input Selection
SWITCH
RESISTOR (
)
1
1.0
2
1.0
3
1.0
4
1.0
5
2.0
6
3.9
7
8.2
8
16.0
INPUT
PGM0
PGM1
PGM2
PGM3
Open
--
--
--
--
REF
S1
S4
S7
S10
BATT-
S2
S5
S8
S11
V+
S3
S6
S9
S12
Evaluates: MAX712/MAX713
Using the Thermistors
Thermistors TR1 and TR2 detect when the battery temper-
ature exceeds the ambient temperature. With two of the
same type of thermistors, as long as the battery tempera-
ture 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 Operat-
ing 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
resis-
tance. Setting R8 to 33k
inhibits fast charging for tem-
peratures 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 V
REF
, and a 22k
resistor to BATT-.
Refer to the Typical Operating Circuit of the MAX712/
MAX713 data sheet.
MAX712 Linear-Mode Evaluation Kit
4
_______________________________________________________________________________________
Table 3. Programming the Timing Functions
TIMEOUT
(min)
Sample
Interval
(s)
SLOPE
LIMIT
PGM2
CONNECTION
PGM3
CONNECTION
S7, S5, S9
S10, S11, S12
SENSE
VOLTAGE
IN TRICKLE
(mV)
22
22
33
33
21
21
21
21
Off
On
Off
On
Open
REF
V+
BATT-
V+
V+
V+
V+
--
S7
S9
S8
S12
S12
S12
S12
4
4
4
4
45
45
66
66
42
42
42
42
Off
On
Off
On
Open
REF
V+
BATT-
Open
Open
Open
Open
--
S7
S9
S8
--
--
--
--
8
8
8
8
90
90
132
132
84
84
84
84
Off
On
Off
On
Open
REF
V+
BATT-
REF
REF
REF
REF
--
S7
S9
S8
S10
S10
S10
S10
16
16
16
16
180
180
264
264
168
168
168
168
Off
On
Off
On
Open
REF
V+
BATT-
BATT-
BATT-
BATT-
BATT-
--
S7
S9
S8
S11
S11
S11
S11
32
32
32
32
Evaluates: MAX712/MAX713
MAX712 Linear-Mode Evaluation Kit
_______________________________________________________________________________________
5
Table 5. Trickle-Charge Sense-Voltage
Selection
Table 4. Programming the Number of Cells
Table 8. Voltage Values
Table 7. Evaluation Board Switch Settings
for Charging Two NiCd AA Cells
(Preshipment Settings)
NUMBER
OF CELLS
PGM0
CONN
PGM1
CONN
S1S3
S4S6
1
2
3
4
V+
V+
V+
V+
V+
Open
REF
BATT-
S3
S3
S3
S3
S6
--
S4
S5
5
6
7
8
Open
Open
Open
Open
V+
Open
REF
BATT-
Open
Open
Open
Open
S6
--
S4
S5
9
10
11
12
REF
REF
REF
REF
V+
Open
REF
BATT-
S1
S1
S1
S1
S6
--
S4
S5
13
14
15
16
BATT-
BATT-
BATT-
BATT-
V+
Open
REF
BATT-
S2
S2
S2
S2
S6
--
S4
S5
Table 6. Factory Settings Before Shipment
PGM3
S10-S12
SENSE VOLTAGE
(mV)
V+
Open
REF
BATT-
S12
--
S10
S11
4
8
16
32
Number of Cells
2
Timeout
264 min
ADC Interval
168 s
Fast-Charge Current
250mA
Trickle-Charge Current
32mA
Battery Temperature Rise Cutoff
+15C
V
LIMIT
2.0V
SWITCH A (SWA)
ON SWITCHES
(ALL OTHERS
OFF)
FUNCTION
PGM0 = V+,
PGM1 = Open
S3,
Indicates two cells
PGM2 = BATT,
PGM3 = BATT
S8, S11
264min timeout,
168s ADC interval,
slope limit on
S1
R
SENSE
= 1.0
Fast-charge current =
250mA
J1
1 & 2
Set for charging two
AA batteries
SWITCH B (SWB)
JUMPER J1
VOLTAGE VALUE
FUNCTION
VREF
2.00
Internal fixed reference voltage
VLIMIT
2.00
Sets maximum charging voltage; R6 is
adjusted to set the level. Set VLIMIT to
VREF for normal operation.
VTHI
1.33
High-temperature trip voltage. Fast
charge ceases when the TEMP pin
exceeds this voltage. R7 is adjusted
to set the level.
VTLO
0.66
Low-temperature trip voltage. Fast
charge will not start when the TEMP
pin is below this voltage. R8 is adjusted
to set the level.
VTEMP
1.00
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.
PDF 
ZIP