ME4057

V01

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

TA 145C PDJA ;

TA 145C (VCC VBAT ) X IBAT X JA

For example: The ME4057 with 5V supply voltage through programmable provides full limiting current 800mA to a

charge lithium-ion battery with 3.75V voltage

. If



JA is 150℃/W ( reference to PCB layout considerations), When

ME4057 begins to decrease the charge current, the ambient temperature about:

TA 145C (5V3.75V ) X (800mA) χ150C / W

TA 145C 0.5W X 150C / W 145C 75C

TA =65C

ME4057 can work in the condition of the temperature is above 65℃, but the charge current will pull down to below

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

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 ME4057

design applications don’t need to considerate the

worst case of thermal condition, this point is importance, because if the junction temperature up to 145℃ ,IC will auto

reduce the power dissipation.

Thermal considerations

Because of the small size of the thin SOP8 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

It will effective to decrease the power dissipation through reduce the voltage of both ends of the inner MOSFET. In

the thermal regulation, this action of transporting current to battery will raise. One of the measure is through an

external component(as a resistor or diode) to consume some power dissipation.

For example: The ME4057 with 5V supply voltage through programmable provides full limiting current 800mA to a

charge lithium-ion battery with 3.75V voltage. If





JA is 125℃/W, so that at 25℃ ambient temperature, the charge

current is calculated to be approximately :

In order to increase the thermal regulation charge current, can decrease the power dissipation of the IC through

reducing the voltage (as show fig.3) of both two ends of the resistor which connecting in series with a 5V AC adapter.

With square equation to calculate IBAT ：

If RCC=0.25Ω, VS=5V, VBAT=3.75V, TA=25℃ and JA =125℃/W, we can calculate the thermal regulation charge

current: IBAT＝948mA. It means that in this structure it can output 800mA full limiting charge current at more high

ambient temperature environment.

Although it can transport more energy and reduce the charge time in this application, but actually spread charge