ACE4704
Fully 5A, 4cell Standalone Li-ion Battery Charger
Where,
f is the switching frequency 300KHz
L is the inductor value
VBAT is the battery voltage
VCC is the input voltage
A reasonable starting point for setting inductor ripple current is △IL＝0.4×ICH, ICH is the charge current.
Remember that the maximum △IL occurs at the maximum input voltage and the lowest inductor value.
So lower charge current generally calls for larger inductor value.
Use Table 2 as a guide for selecting the correct inductor value for your application.
Charge Current
1A
Input Voltage
>20V
Inductor Value
40uH
<20V
30uH
30uH
>20V
2A
3A
4A
5A
20uH
<20V
20uH
>20V
15uH
<20V
15uH
>20V
10uH
<20V
10uH
>20V
8uH
<20V
Table 2 Guide to Select Inductor Value
MOSFET Selection
The ACE4704 uses a P-channel power MOSFET switch. The MOSFET must be selected to meet the
efficiency or power dissipation requirements of the charging circuit as well as the maximum temperature
of the MOSFET. The peak-to-peak gate drive voltage is set internally, this voltage is typically 6.5V.
Consequently, logic-level threshold MOSFETs must be used. Pay close attention to the BVDSS
specification for the MOSFET as well; many of the logic level MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFET includes the “on” resistance Rds(on), total gate charge Qg,
reverse transfer capacitance CRSS, input voltage and maximum charge current.
The MOSFET power dissipation at maximum output current is approximated by the equation:
VER 1.2
10
ACE [ ACE TECHNOLOGY CO., LTD. ]
