Datasheet

MAX846A
Cost-Saving Multichemistry
Battery-Charger System
6 _______________________________________________________________________________________
______________________________________________________________Pin Description
PIN FUNCTION
6
Float-Voltage Reference-Adjust Input. Leave VSET open for a 4.2V default. See the Applications
Information section for adjustment information.
NAME
4 Ground
3
Current-Regulation-Loop Compensation Pin. Connect a compensation capacitor (typically 10nF) from
CCI to VL.
2
3.3V, 20mA, 1% Linear-Regulator Output. VL powers the system µC and other components. Bypass to
GND with a 4.7µF tantalum or ceramic capacitor.
1 Supply Input from External DC Source. 3.7V ≤ V
DCIN
≤ 20V.
5
Voltage-Regulation-Loop Compensation Pin. Connect a compensation capacitor (typically 10nF) from
CCV to VL.
VSET
CCV
GND
CCI
VL
DCIN
7 ISET
Current-Set Input/Current-Monitor Output. ISET sets the current-regulation point. Connect a resistor
from ISET to GND to monitor the charging current. ISET voltage is regulated at 1.65V by the current-
regulation loop. To adjust the current-regulation point, either modify the resistance from ISET to ground
or connect a fixed resistor and adjust the voltage on the other side of the resistor (Figure 5). The
transconductance of the current-sense amplifier is 1mA/V.
8 OFFV Logic Input that disables the voltage-regulation loop. Set OFFV high for NiCd or NiMH batteries.
9 PWROK
Open-Drain, Power-Good Output to µC. PWROK is low when VL is less than 3V. The reset timeout peri-
od can be set externally using an RC circuit (Figure 3).
10 CELL2
Digital Input. CELL2 programs the number of Li-Ion cells to be charged. A high level equals two cells; a
low level equals one cell.
11 ON
Charger ON/OFF Input. When low, the driver section is turned off and I
BATT
<1µA. The VL regulator is
always active.
12 BATT Battery Input. Connect BATT to positive battery terminal.
13 CS+
Current-Sense Amplifier High-Side Input. Connect CS+ to the sense resistor’s power-source side. The
sense resistor may be placed on either side of the pass transistor.
14 CS- Current-Sense Amplifier Low-Side Input. Connect CS- to the sense resistor’s battery side.
15 PGND Power Ground
16 DRV External Pass Transistor (P-channel MOSFET or PNP) Base/Gate Drive Output. DRV sinks current only.
_______________Detailed Description
The MAX846A battery-charging controller combines
three functional blocks: a 3.3V precision, low-dropout
linear regulator (LDO), a precision voltage reference,
and a voltage/current regulator (Figure 1).
Linear Regulator
The LDO regulator output voltage (VL) is two times the
internal reference voltage; therefore, the reference and
LDO track. VL delivers up to 20mA to an external load
and is short-circuit protected. The power-good output
(PWROK) provides microcontroller (µC) reset and
charge-current inhibition.
Voltage Reference
The precision internal reference provides a voltage to
accurately set the float voltage for lithium-ion (Li-Ion)
battery charging. The reference output connects in
series with an internal, 2%-accurate, 20kΩ resistor. This
allows the float voltage to be adjusted using one exter-
nal 1% resistor (R
VSET
) to form a voltage divider
(Figure 4). The float-voltage accuracy is important for
battery life and to ensure full capacity in Li-Ion batter-
ies. Table 1 shows the accuracies attainable using the
MAX846A.