General Description
The MAX8725 evaluation kit (EV kit) is an accurate and
efficient multichemistry battery charger. The EV kit can
charge three or four series Li+ cells with a current up to
3A. Charge current and input-source current are
adjustable using on-board potentiometers. The output
voltage is set to 4.2V ✕ the number of series cells in the
battery pack. The number of series cells is jumper selectable. The output voltage is adjustable between 4V to
4.4V (
✕ the number of series cells) by installing two resis-
tors. The EV kit provides outputs to monitor the ACadapter current and the presence of an AC adapter.
The MAX8725 automatically selects the power path for
supplying power to the system by controlling two external
p-channel MOSFETs. This decision is made based on the
presence of an AC adapter.
Features
♦ Input Current Limiting
♦ ±0.5% Output Voltage Accuracy Using Internal
Reference
♦ Automatic Selection of System Power Source
♦ Analog Inputs Control Charge Current and
Charge Voltage
♦ Monitor Outputs for
AC Adapter Current
AC Adapter Presence
♦ Up to 17.6V Battery Voltage
♦ +8V to +25V Input Voltage
♦ Up to 3A Battery-Charge Current
♦ Charges Li+, NiCd, and NiMH Battery Chemistries
♦ Surface-Mount Construction
♦ Fully Assembled and Tested
Evaluates: MAX8725
MAX8725 Evaluation Kit
________________________________________________________________ Maxim Integrated Products 1
Component List
19-0292; Rev 0; 5/05
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.
Ordering Information
PART TEMP RANGE IC PACKAGE
MAX8725EVKIT 0°C to +70°C 28 Thin QFN
DESIGNATION QTY DESCRIPTION
10µF ±20%, 25V X5R ceramic
C1, C2 2
capacitors (1812)
Taiyo Yuden TMK432BJ106KM,
TDK C4532X5R1E106M
C3 0 Not installed (2220)
22µF ±20%, 25V ceramic capacitor
C4 1
(2220)
TDK C5750X5R1E226M
C5, C6 0 Not installed, E-size capacitors
C7, C8, C9
C13, C14, C15
0 Not installed, capacitors (0603)
1µF ±10%, 6.3V X5R ceramic
capacitors (0603)
C10, C11, C21 3
Murata GRM188R60J105K,
Taiyo Yuden JMK107BJ105KA,
TDK C1608X5R1A105K
0.1µF ±10%, 25V X7R ceramic
C12, C17, C18 3
capacitors (0603)
Murata GRM188R71E104K,
TDK C1608X7R1E104K
DESIGNATION QTY DESCRIPTION
1µF ±10%, 25V X7R ceramic
capacitor (1206)
C16 1
C19, C20 2
C22 1
D1 1
D2 0 Not installed
Murata GRM31MR71E105K,
Taiyo Yuden TMK316BJ105KL,
TDK C3216X7R1E105K
0.01µF ±10%, 50V X7R ceramic
capacitors (0603)
Murata GRM188R71H103K,
Taiyo Yuden UMK107B103KZ,
TDK C1608X7R1H103K
2.2µF ±20%, 35V tantalum capacitor
(B-size)
AVX TAJB225M035
Kemet T491B225M035AS
Schottky diode, 0.5A, 30V SOD-123
Diodes Inc. B0530W,
General Semiconductor MBR0530,
ON Semiconductor MBR0530
Evaluates: MAX8725
MAX8725 Evaluation Kit
2 _______________________________________________________________________________________
SUPPLIER PHONE FAX WEBSITE
AVX 843-946-0238 843-626-3123
www.avxcorp.com
Diodes Inc. 805-446-4800 805-381-3899
www.diodes.com
Fairchild Semiconductor 888-522-5372 —
www.fairchildsemi.com
General Semiconductor 760-804-9258 760-804-9259
www.gensemi.com
International Resistive Co.
361-992-7900 361-992-3377
www.irctt.com
Kemet 864-963-6300 864-963-6322
www.kemet.com
Murata 770-436-1300 770-436-3030
www.murata.com
ON Semiconductor 602-244-6600 602-244-4545
www.onsemi.com
Sumida 847-545-6700 847-545-6720
www.sumida.com
Taiyo Yuden 800-348-2496 847-925-0899
www.t-yuden.com
TDK 847-803-6100 847-390-4405
www.component.tdk.com
TOKO 847-297-0070 847-699-1194
www.tokoam.com
Vishay Dale 402-564-3131 402-563-6296
www.vishay.com
Component Suppliers
Component List (continued)
DESIGNATION
QTY
DESCRIPTION
J1
Smart battery header assembly, right
angle, keyless, five position
Tyco Electronics (AMP) 787441-1
JU1, JU2
2-pin headers
JU3
Not installed
L1
10µH, 4.4A inductor
Sumida CDRH104R-100NC,
TOKO 919AS-100M
N1
Single, n-channel, 8.4A, 30V, 8-pin
SO MOSFET
Fairchild FDS6612A
P1
Single, p-channel, -5.3A, -30V, 8-pin
SO MOSFET
Fairchild FDS9435A
P2, P3, P4
Single, p-channel, -11A, -30V, 8-pin
SO MOSFETs
Fairchild FDS6675
Note: Indicate you are using the MAX8725 when contacting these manufacturers.
1
2
0
1
1
1
3
DESIGNATION QTY DESCRIPTION
0.01Ω ± 1%, 0.5W sense r esi stor ( 2010)
R1 1
R2 1
R3, R4, R8,
R13, R14, R15,
R17–R23
R5 1 590kΩ ±1% resistor (0603)
R6 1 196kΩ ±1% resistor (0603)
R7, R12 2 50kΩ potentiometers (multiturn)
R9, R10, R11 3 10kΩ ±5% resistors (0603)
R16 1 33Ω ±5% resistor (0603)
R24 1 10Ω ±5% resistor (0603)
U1 1 MAX8725ETI (28-pin thin QFN-EP)
Vishay Dale WSL2010 0.010 1.0%,
IRC LRC-LR2010-01-R010-F
0.015Ω ±1%, 0.5W sense resistor
(2010)
Vishay Dale WSL2010 0.015 1.0%,
IRC LRC-LR2010-01-R015-F
0 Not installed, resistors (0603)
Evaluates: MAX8725
MAX8725 Evaluation Kit
_______________________________________________________________________________________ 3
Quick Start
Required Equipment
Before beginning, the following equipment is required:
• DC source to supply the input current to the charger;
this source must be capable of supplying a voltage
greater than the battery-voltage set point and have
sufficient current rating
• Voltmeter
• Battery pack or load
Procedure
The MAX8725 EV kit is a fully assembled and tested
surface-mount board. Follow the steps below to verify
board operation. Do not turn on the power supply
until all connections are completed. Observe all precautions on the battery manufacturer’s data sheet:
1) Set jumper JU1 to indicate the number of cells in
the battery pack (Table 1).
2) Remove the shunt on JU2 to disable the MAX8725.
3) The battery-regulation voltage is set to 4.2V per cell.
If a different voltage is required, see the Battery
Regulation Voltage section.
4) The charge current is set to 3A. If a different current
is required, see the Charging Current Limit section.
5) The source current is set to 5A. If a different current
is required, see the Source Current Limit section.
6) Connect the input current supply across the
ADAPTER_IN and PGND pads.
7) Connect a battery pack or load between the BATT+
and BATT- pads.
8) Turn on the power supply.
9) Enable the MAX8725 by installing the shunt on JU2.
10) Verify current is being delivered to the battery.
Detailed Description
The MAX8725 includes all the functions necessary to
charge Li+ batteries. The EV kit is shipped with a
charge current of 3A and a battery-regulation voltage of
4.2V x the number of cells in the battery pack.
The MAX8725 includes a battery-conditioning feature,
which allows for the relearning of the battery-pack
capacity. For more information on the operation of the
MAX8725, refer to the Detailed Description section of
the MAX1909/MAX8725 data sheet.
Jumper JU1
Jumper JU1 selects the number of series cells to be
charged. See Table 1 for jumper settings.
Jumper JU2
Jumper JU2 controls the pack-presence PKPRES pin. A
shunt on JU2 enables the MAX8725. Removing the
shunt places the MAX8725 in shutdown mode.
If the battery pack used with the MAX8725 EV kit has a
thermistor, remove the shunt on JU2 and connect the
thermistor to the THRM pad.
Jumper JU3
Jumper JU3 connects VCTL to LDO. This sets the battery-regulation voltage to 4.2V x the number of cells.
The battery-regulation voltage can be set between 4.0V
and 4.4V (x the number of cells) by cutting the short
across JU3 and installing resistors at R3 and R4. See the
Battery-Regulation Voltage section for more information.
Battery-Regulation Voltage
The default battery-regulation voltage on the MAX8725
EV kit is 4.2V x the number of cells. To set it to a value
between 4.0V and 4.4V (x the number of cells), remove
the shunt on JU1 and install resistors at R3 and R4. Use
the following equation to calculate the resistor values:
RR
V
CELLS
BATT
34
54
9 523 4 223 1 8
1=
−
+
−
.
...
JUMPER
JUMPER
FUNCTION
MODE = LDO. Cell count = 4.
JU1
Open MODE = float. Cell count = 3.
PKPRES = GND. MAX8725 enabled.
JU2
Open
PKPRES connected to LDO through
10kΩ pullup resistor. The MAX8725 is
disabled unless the battery thermistor
is connected to THRM.
C l osed *
( shor ted b y
VCTL = LDO. Battery-regulation
voltage set to 4.2V x the number of
cells.
JU3
Open
Battery-regulation voltage can be set
between 4V and 4.4V x the number of
cells. Resistors R3 and R4 must be
installed.
Table 1. Jumper Selection
*Default position.
POSITION
Closed*
Closed*
P C tr ace)
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