UB2017

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 13

www.unisonic.com.tw

QW-R502-868.a

OPERATION(Cont.)

5. Thermal Limiting

An internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to rise

above a preset value of approximately 120°С. This feature protects the UTC UB2017 from excessive temperature

and allows the user to push the limits of the power handling capability of a given circuit board without risk of

damaging the UTC UB2017. The charge current can be set according to typical (not worst-case) ambient

temperature with the assurance that the charger will automatically reduce the current in worst-case conditions.

6. Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until

Furthermore, to protect against reverse current in the power MOSFET, the UVLO circuit keeps the charger in

APPLICATION INFORMATION

Stability Considerations

The constant-voltage mode feedback loop is stable without an output capacitor provided a battery is connected to

the charger output. With no battery present, an output capacitor is recommended to reduce ripple voltage. When

using high value, low ESR ceramic capacitors, it is recommended to add a 1W resistor in series with the capacitor.

No series resistor is needed if tantalum capacitors are used. 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 20kΩ.

However, additional capacitance on this node reduces the maximum allowed program resistor thus it should be

avoided. Average, rather than instantaneous, charge current may be of interest to the user. For example, if a

switching power supply operating in low current mode is connected in parallel with the battery, the average current

being pulled out of the BAT pin is typically of more interest than the instantaneous current pulses. In such a case, a

simple RC filter can be used on the PROG pin to measure the average battery current as shown in Figure 1. A 10kΩ

resistor has been added between the PROG pin and the filter capacitor to ensure stability.

Fig. 1 Isolating Capacitive Load on PROG Pin