ME4057

V01

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Fig.1 State diagram of a typical charge cycle

Fig.2 Isolating with capacitive load on PROG Pin

Stability Considerations

In constant-current mode, the PROG pin is in the feedback loop, not the battery. The constant-current mode

stability is affected by the impedance at the PROG pin. With no additional capacitance on the PROG pin, the charger

is stable with program resistor values as high as 20K

Ω. However, additional capacitance on this node reduces the

maximum allowed program resistor. Therefore, if IPROG pin is loaded with a capacitance C, the following equation

should be used to calculate the maximum resistance value for RPROG：

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

instantaneous current. In this case, In order to measure average charge current or isolate capacitive load from IPROG

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

Ω

resistor between PROG pin and filter capacitor.

Power dissipation

The conditions that cause the ME4057 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: PD (VCC VBAT ) X I BAT

ME4057