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PROG

5

PROG

1

R

2 10 C







As user, may think charge current is important, not instantaneous current. For example, to run a low current

mode switch power which parallel connected with battery, the average current from BAT pin usually importance to

pin, a simple RC filter can be used on PROG pin as shown in Figure 2. In order to ensure the stability add a 10KΩ

resistor between PROG pin and filter capacitor.

Power dissipation

The conditions that cause the HM4055 to reduce charge current through thermal feedback can be

approximated by considering the power dissipated in the IC. Nearly all of this power dissipation is generated by the

internal MOSFET-this is calculated to be approximately:

The approximate ambient temperature at which the thermal feedback begins to protect the IC is:

For example: The HM4055 with 5V supply voltage through programmable provides full limiting current 800mA

to a charge lithium-ion battery with 3.75V voltage

HM4055 begins to decrease the charge current, the ambient temperature about:

X 150C / W 110C 75C

HM4055 can work in the condition of the temperature is above 35℃, but the charge current will pull down to

below 800mA. In a fixed ambient temperature, the charge current is calculated to be approximately :

A

BAT

BAT

JA

110℃ -T

I=

(VCC - V )*θ

Just as Description of the Principle part talks about so, the current on PROG pin will reduce in proportion to the

reduced charge current through thermal feedback. In HM4055 design applications don’t need to considerate the

worst case of thermal condition, this point is importance, because if the junction temperature up to 110℃ ,IC will auto

reduce the power dissipation.

Thermal considerations

Because of the small size of the thin SOT23-5 package, it is important to use a good thermal PC board layout to

maximize the available charge current. The thermal path for the heat generated by the IC is from the die to the

copper lead frame, through the package leads, (especially the ground lead) to the PC board copper. The PC board

copper is the heat sink. The footprint copper pads should be as wide as possible and expand out to larger copper

areas to spread and dissipate the heat to the surrounding ambient. Other heat sources on the board, not related to

the charger, must also be considered when designing a PC board layout because they will affect overall temperature

rise and the maximum charge current.

Add thermal regulation current

HM4055A