LTC4059_15 Datasheet, PDF (10/12 Pages) Linear Technology – 900mA Linear Li-Ion Battery Chargers with Thermal Regulation in 2 2 DFN

LTC4059/LTC4059A
APPLICATIO S I FOR ATIO
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_PROG, the following equa-
tion should be used to calculate the maximum resistance
value for R_PROG:
R_PROG
≤
2π
•
5
1
• 10⁵
•
C_PROG
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 4. A 20k resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
V_CC Bypass Capacitor
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.
LTC4059
PROG
GND
20k
R_PROG
CHARGE CURRENT
MONTIOR CIRCUITRY
C_FILTER
4059 F04
Figure 4. Isolating Capacitive Load on PROG Pin and Filtering
Figure 5. Photo of Typical Circuit (2.5mm × 2.7mm)
4059fb
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