MAX1873 Maxim, MAX1873 Datasheet - Page 9

• Manufacturer Part Number: MAX1873
• Description: Simple Current-Limited Switch-Mode Li Charger Controller
• Manufacturer: Maxim

Figure 1. Typical Application Circuit
The MAX1873 includes all of the functions necessary to
charge 2-, 3-, or 4-series cell lithium-ion (Li+) battery
packs. It includes a high-efficiency step-down DC-DC
converter that controls charging voltage and current. It
also features input source current limiting so that an AC
adapter that supplies less than the total system current
in addition to charging current can be used without fear
of overload.
The DC-DC converter uses an external P-channel MOS-
FET switch, inductor, and diode to convert the input volt-
age to charging current or charging voltage. The typical
application circuit is shown in Figure 1. Charging current
is set by R
BATT. The battery regulation voltage limit is nominally
set to 8.4V for the R version (2-cells), 12.6V for the S
version (3-cells), and 16.8V for the T version (4-cells),
DISABLE
CSB
(9V MIN FOR 2- CELLS)
, while the battery voltage is measured at
N
VIN 17V TO 28V
_______________________________________________________________________________________
Detailed Description
100kΩ
200mV ON R
C
0.1µF
Simple Current-Limited Switch-Mode
4V OUT PER
CCVS
0.22µF
MBR5340
C
DCIN
D1
C
47nF
C
C
47nF
CCVP
1nF
10kΩ
R
CCS
CC
CSB
CCV
0.22µF
C
VH
CCI
CCS
CCV
DCIN
IOUT
ICHG/EN
VH
MAX1873
VL
2.2µF
C
VL
CSSN
CSSP
VADJ
BATT
GND
CSB
REF
EXT
C
1µF
REF
C
0.01µF
C
0.01µF
but it can also be adjusted to other voltages for differ-
ent Li+ chemistries.
Li+ batteries require a high-accuracy voltage limit while
charging. The battery regulation voltage is nominally
set to 4.2V per cell and can be adjusted ±5.25% by
setting the voltage at VADJ between REF and ground.
By limiting the adjust range of the regulation voltage, an
overall voltage accuracy of better than ±0.75% is main-
tained while using 1% resistors.
An internal error amplifier maintains voltage regulation
to within ±0.75%. The amplifier is compensated at CCV
(see Figure 1). Individual compensation of the voltage
regulation and current regulation loops allows for opti-
mal compensation of each. A typical CCV compensa-
tion network is shown in Figure 1 and will suffice for
most designs.
4.7Ω
N
P
4.7Ω
R
Li+ Charger Controller
R
P
N
R1
R2
0.033Ω
P
R
CSS
MBR5340
10µH
L1
D2
0.068Ω
R
CSB
C
47µF
L
Voltage Regulator
(2- TO 4-CELLS)
C
68µF
BATTERY
BATT
SYSTEM
LOAD
LI+
9