LTC4064

14

sn4064 4064fs

PROG pin. With no additional capacitance on the PROG

pin, stability is acceptable with program resistor values as

high as 50k. However, additional capacitance on this node

reduces the maximum allowed program resistor. The pole

frequency at the PROG pin should be kept above 500kHz.

Therefore, if the PROG pin is loaded with a capacitance, C,

the following equation should be used to calculate the

5

7

CHARGE

CURRENT

MONITOR

CIRCUITRY

10k

LTC4064

GND

PROG

Figure 5. Isolating Capacitive Load on PROG Pin and Filtering

APPLICATIO S I FOR ATIO

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

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

battery current as shown in Figure 5. A 10k resistor is

added between the PROG pin and the filter capacitor and

monitoring circuit to ensure stability.