AK7903 Datasheet, PDF (7/10 Pages) Asahi Kasei Microsystems – DCDC Step-down Converter for NiH2 Battery

[AK7903]
OPERATION OVERVIEW
■Input and Output
AK7903 is a DCDC converter which power MOSFET is built-in, and input voltage support 4.1V～5.5V; the device is
the most suitable charger for NiH2 battery system which used 1 or 2 series NiH2 battery. In the case of charging to 1
cell, the characteristic can be guaranteed even input voltage below 3.8V. AK7903 detects external resister current
through FB and SENSE pins, and it regulates switching regulator output voltage in order to maintain DCDC output
current fixed. When the SENSE resistor current decreased, DCDC output voltage will be increased, so output current
increase with coil current limitation (1.0A @typ). SENSE resistor is recommended less than 0.353Ω. Use small size
SENSE resistor, the charge current is possible not reach set current.
■Protection Functions
AK7903 is built-in over current protection circuit and thermal protection circuit for preventing device be damaged.
Protection condition and recovery method is showed at Table 1.
Protection Function
Current Limit
(Including Output
Short to Ground)
Thermal Shut-Down
Working Condition
Device Condition
Coil current 1.0A
PMOS= OFF in the case that
coil current > 1.0A. It will be
judged at every cycle.
Chip temperature
exceed 120℃(typ)
Switching Stop
Table 1. Protection Function
Recovery Condition
Auto recovery when left
condition is cancelled.
Auto recovery when chip
temperature below 100℃(typ).
■Output PMOS Bulk Control
AK7903 controls output PMOS bulk, so is the most suitable construction for system environment.
■ Gain Switching for OP-AMP
Table 2 shows OP-AMP gain setting.
EN2
CONT
SW1
SW2
SW3
0
0 or 1
OFF
OFF
OFF
1
0
ON
OFF
ON
1
1
OFF
ON
ON
Table 2. OP-AMP gain setting
オペアンプ
Power-down
Gain=3.75 times
Gain=1.96 times
MS1190-E-00
7
2010/6