UB2017

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

9 of 13

www.unisonic.com.tw

QW-R502-868.a

APPLICATION INFORMATION(Cont.)

Increasing Thermal Regulation Current

Reducing the voltage drop across the internal MOSFET can significantly decrease the power dissipation in the IC.

This has the effect of increasing the current delivered to the battery during thermal regulation. One method is by

dissipating some of the power through an external component, such as a resistor or diode. While this application

delivers more energy to the battery and reduces charge time in thermal mode, it may actually lengthen charge time

in voltage mode if VCC becomes low enough to put the UTC UB2017 into dropout. Figure 2 shows how this circuit

can result in dropout as RCC becomes large. This technique works best when RCC values are minimized to keep

component size small and avoid dropout. Remember to choose a resistor with adequate power handling capability.

UTC

UB2017

PROG

BAT

2kΩ

+

Li-Ion

BATTERY

1µF

GND

5V

Fig. 2 A Circuit to Maximize Thermal Mode Charge Current

VCC Bypass Capacitor

Many types of capacitors can be used for input bypassing. However, caution must be exercised when using

multilayer ceramic capacitors. Because of the self-resonant and high Q characteristics of some types of ceramic

capacitors, high voltage transients can be generated under some start-up conditions, such as connecting the charger

input to a live power source. Adding a 1 W resistor in series with an X5R ceramic capacitor will minimize start-up

voltage transients.

Charge Current Soft-Start

The UTC UB2017 includes a soft-start circuit to minimize the inrush current at the start of a charge cycle. When a

charge cycle is initiated, the charge current ramps from zero to the full-scale current over a period of approximately

50ms. This has the effect of minimizing the transient current load on the power supply during start-up.