Datasheet


   
   
SLVS216B − JUNE 1999 − JUNE 2008
14
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
capacitor selection
The TPS60111 requires only four external capacitors as shown in the basic application circuit. Their values are
closely linked to the output current capacity, output noise requirements, and mode of operation. Generally, the
transfer capacitors (C
xF
) will be the smallest.
The input capacitor improves system efficiency by reducing the input impedance and stabilizes the input current.
C
IN
is recommended to be about two to four times as large as C
xF
.
The output capacitor (C
O
) can be selected from 8-times to 50-times larger than C
xF
, depending on the mode
of operation and ripple tolerance
†
. Tables 3 and 4 show capacitor values recommended for low
quiescent-current operation (pulse-skip mode) and for low output voltage ripple operation (constant-frequency
mode). A recommendation is given for smallest size.
Table 3. Recommended Capacitor Values for Low Quiescent-Current Operation
†
(pulse-skip mode)
V
IN
[V]
I
O
[mA]
C
IN
[µF]
C
xF
[µF]
C
O
[µF]
OUTPUT
VOLTAGE
RIPPLE V
PP
IN
[V]
I
O
[mA]
TANTALUM CERAMIC
xF
[
µ
F]
TANTALUM CERAMIC
RIPPLE V
PP
[mV]
3.6 75 4.7 1 15 150
3.6 75 4.7 (X7R) 1 10 (X5R) 105
3.6 150 4.7 1 15 150
3.6 150 4.7 (X7R) 1 10 (X5R) 105
†
All measurements are done with additional 1-µF X7R ceramic capacitors at input and output.
Table 4. Recommended Capacitor Values for Low Output Voltage Ripple Operation
†
(constant-frequency mode)
V
IN
[V]
I
O
[mA]
C
IN
[µF]
C
xF
[µF]
C
O
[µF]
OUTPUT
VOLTAGE
RIPPLE V
PP
IN
[V]
O
[mA]
TANTALUM CERAMIC
xF
[
µ
F]
TANTALUM CERAMIC
RIPPLE V
PP
[mV]
3.6 75 4.7 1 33 10
3.6 75 4.7 (X7R) 1 22 + 10, (X5R) 6
3.6 150 4.7 1 33 17
3.6 150 4.7 (X7R) 1 22 + 10, (X5R) 10
†
All measurements are done with additional 1-µF X7R ceramic capacitors at input and output.
†
In constant-frequency mode always select C
O
≥ 33 µF