Datasheet

DV
out
+
I
out
C
out
ƪ
1
f
s
*
I
p
L
V
out
) V
d
* V
in
ƫ
) I
p
ESR
TPS65100-Q1
SLVS849A –JULY 2008–REVISED APRIL 2012 www.ti.com
Output Capacitor Selection
For the best output voltage filtering, a low ESR output capacitor is recommended. Ceramic capacitors have a low
ESR value, but depending on the application, tantalum capacitors can be used as well. A 22-μF ceramic output
capacitor works for most of the applications. Higher capacitor values can be used to improve the load transient
regulation. See Table 2 for selection of the output capacitor. The output voltage ripple can be calculated as:
with:
IP = Peak switch current as calculated in the previous section with I
SW(peak)
.
L = Selected inductor value
I
OUT
= Normal load current
f
s
= Switching frequency
V
d
= Rectifier diode forward voltage (typical 0.3 V)
C
OUT
= Selected output capacitor
ESR = Output capacitor ESR value
Input Capacitor Selection
For good input voltage filtering, low ESR ceramic capacitors are recommended. A 22-μF ceramic input capacitor
is sufficient for most of the applications. For better input voltage filtering, this value can be increased. See
Table 2 and the typical applications for input capacitor recommendations.
Table 2. Input and Output Capacitors Selection
CAPACITOR VOLTAGE RATING COMPONENT SUPPLIER COMMENTS
22 μF/1210 16 V Taiyo Yuden EMK325BY226MM C
out
22 μF/1206 6.3 V Taiyo Yuden JMK316BJ226 C
in
Rectifier Diode Selection
To achieve high efficiency, a Schottky diode should be used. The voltage rating should be higher than the
maximum output voltage of the converter. The average forward current should be equal to the average inductor
current of the converter. The main parameter influencing the efficiency of the converter is the forward voltage and
the reverse leakage current of the diode; both should be as low as possible. Possible diodes are: On
Semiconductor MBRM120L, Microsemi UPS120E, and Fairchild Semiconductor MBRS130L.
Converter Loop Design and Stability
The TPS65100 converter loop can be externally compensated and allows access to the internal
transconductance error amplifier output at the COMP pin. A small feedforward capacitor across the upper
feedback resistor divider speeds up the circuit as well. To test the converter stability and load transient
performance of the converter, a load step from 50 mA to 250 mA is applied, and the output voltage of the
converter is monitored. Applying load steps to the converter output is a good tool to judge the stability of such a
boost converter.
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