LTC4059/LTC4059A

10

4059fa

program resistor. The pole frequency at the PROG pin

should be kept above 500kHz. Therefore, if the PROG pin

tion should be used to calculate the maximum resistance

R

C

PROG

PROG

≤

π

1

••

•

Average, rather than instantaneous, battery 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

APPLICATIO S I FOR ATIO

filter can be used on the PROG pin to measure the average

battery current as shown in Figure 4. A 20k resistor has

been added between the PROG pin and the filter capacitor

to ensure stability.

Many types of capacitors can be used for input bypassing;

however, caution must be exercised when using multi-

layer ceramic capacitors. Because of the self-resonant and

high Q characteristics of some types of ceramic capaci-

tors, high voltage transients can be generated under some

start-up conditions, such as connecting the charger input

to a live power source. For more information, refer to

Application Note 88.

Figure 4. Isolating Capacitive Load on PROG Pin and Filtering

Figure 5. Photo of Typical Circuit (2.5mm

× 2.7mm)

LTC4059

CHARGE CURRENT

MONTIOR CIRCUITRY

20k

4059 F04

PROG

GND