ACE4702 datasheet(11/15 Pages) ACE

11 / 15 page

ACE4702

2 Cell Li-ion Battery Charger IC

VER 1.1

Use Table 2 as a guide for selecting the correct inductor value for your application.

Charge Current

Input Voltage

Inductor Value

>20V

40uH

<20V

30uH

>20V

30uH

<20V

20uH

>20V

20uH

<20V

15uH

>20V

15uH

<20V

10uH

>20V

10uH

<20V

8uH

Table 2 Guide to Select Inductor Value

MOSFET Selection

The ACE4702 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 5.8V. 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:

Where:

Pd is the power dissipation of the power MOSFET

VBAT is the maximum battery voltage

VCC is the minimum input voltage

Rds(on) is the power MOSFET’s on resistance at room temperature

ICH is the charge current

dT is the temperature difference between actual ambient temperature and room temperature(25℃) In

addition to the I

ds(on) loss, the power MOSFET still has transition loss, which are highest at the highest

input voltage. Generally speaking, for VIN＜20V, the I

ds(on) loss may be dominant, so the MOSFET with

lower Rds(on) should be selected for better efficiency; for VIN＞20V, the transition loss may be dominant, so

the MOSFET with lower CRSS can provide better efficiency. CRSS is usually specified in the MOSFET

characteristics; if not, then CRSS can be calculated using CRSS = QGD

/ΔV

DS.

The MOSFETs such as ACE9435, ACE4443, ACE7401, ACE4409 can be used. The part numbers listed

above are for reference only, the users can select the right MOSFET based on their requirements.

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