HM5902 datasheet(13/15 Pages) HMSEMI

13 / 15 page

Application Information

Power Dissipation

The conditions that cause the HM5902 to reduce charge current through thermal feedback can be

approximated by considering the power dissipated in the IC. For high charge current, the HM5902

power dissipation is approximately:

PD= (VIN-VBAT)．IBAT

Where PD is the power dissipated, VCC is the input supply voltage, VBAT is the battery voltage and

IBAT is the charge current. It is not necessary to check any worst-case power dissipation scenarios

because the HM5902 will automatically reduce the charge current to maintain the die temperature

under 140°C approximately. The approximate ambient temperature at which the thermal feedback

begins to protect the IC is:

TA=140°C – PDθJA

=140°C – (VIN-VBAT)．IBAT．θJA

For example: Consider an HM5902 operating from a 5V wall adapter providing 0.5A to a 4.0V

Li-Ion battery. The ambient temperature above which the HM5902 will begin to reduce the 0.5A charge

current is approximately:

TA = 140°C – (5V – 4.0V) • (0.5A) • 60°C/W

= 140°C – 0.5W • 60°C/W = 140°C – 30°C

= 110°C

The HM5902 can be used above 110°C, but the charge current will be reduced to smaller than

500mA. The approximate current at a given ambient temperature can be calculated:

IBAT =

(

) JA

•

BAT

140

Using the previous example with an ambient temperature of 90°C, the charge current will be

reduced to approximately:

IBAT = (

)

C/W

3.6V

140

•

= 595mA

HM5902 Datasheet(PDF) 13 Page - Shenzhen Huazhimei Semiconductor Co., Ltd