UB2012

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

15 of 17

www.unisonic.com.tw

QW-R121-018 .G

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APPLICATION INFORMATION(Cont.)

SELECTING INPUT CAPACITOR

In most applications, a high-frequency decoupling capacitor is required. A 0.1μF ceramic, placed in proximity to

VCC and VSS pins, works well. The UTC UB2012 works with both regulated and unregulated external dc supplies. If

a non-regulated supply is chosen, the supply unit should have enough capacitance to hold up the supply voltage to

the minimum required input voltage at maximum load, otherwise more capacitance must be added to the input of the

charger.

SELECTING OUTPUT CAPACITOR

For loop stability, the UTC UB2012 does not require any output capacitor. However, when a battery is not

present, the user can add output capacitance in order to control the output voltage. The charger quickly charges the

output capacitor to the regulation voltage, but the output voltage decays slowly, because of the low leakage current

on the BAT pin, down to the recharge threshold. Addition of a 0.1μF ceramic capacitor, for instance, results in a 100

mV (pp) ripple waveform, with an approximate frequency of 25Hz. Higher capacitor values can be used if a lower

frequency is desired.

AUTOMATIC CHARGE-RATE COMPENSATION

In order to compensate safely for internal impedance of the battery pack, the UTC UB2012 uses the automatic

charge-rate compensation technique to reduce charging time. The automatic charge-rate compensation feature is

Fig. 12 outlines the main components of a single-cell Li-Ion battery pack. The Li-Ion battery pack consists of a

cell, protection circuit, fuse, current sense-resistors, connector, and some wiring. There are some resistances in

each of these components. Total impedance of the battery pack is equal to the sum of the minimum resistances of

all battery-pack components. Using the minimum resistance values reduces the odds for overcompensating.

Overcompensating may activate the safety circuit of the battery pack.

BAT+

Terminal

Fuse

BAT-

Wire

Terminal

Discharge

Charge

Wire

Wire

Cell

Wire

Protection

Controller

Fig. 10 Typical Components of a Single-Cell Li-lon Pack

Compensation is achieved through input pin COMP (Fig. 13). A portion of the current-sense voltage, presented

increases the output voltage to compensate for the battery pack’s internal impedance and for undesired voltage

drops in the circuit.