TPS657052_1 Datasheet, PDF (19/24 Pages) Texas Instruments – PMU for Embedded Camera Module

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TPS657052
TPS657051
SLVSA08 – FEBRUARY 2010
Output Capacitor Selection
The advanced Fast Response voltage mode control scheme of the step-down converter allows the use of small
ceramic capacitors with a typical value of 10µF, without having large output voltage under and overshoots during
heavy load transients. Ceramic capacitors having low ESR values result in lowest output voltage ripple and are
therefore recommended. For an inductor value of 2.2µH, an output capacitor with 10µF can be used. Refer to
recommended components.
If ceramic output capacitors are used, the capacitor RMS ripple current rating will always meet the application
requirements. Just for completeness the RMS ripple current is calculated as:
Vout
1-
I_RMSCout = Vout ´
Vin
L´ ¦
1
´
2´ 3
(4)
At nominal load current the inductive converters operate in PWM mode and the overall output voltage ripple is
the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and
discharging the output capacitor:
DVout = Vout ´
1- ^Vout
Vin
L´ ¦
´
æ
ç
è
8
1
´ Cout ´
¦
ö
+ ESR _÷
ø
(5)
Where the highest output voltage ripple occurs at the highest input voltage Vin.
At light load currents the converter operates in Power Save Mode and the output voltage ripple is dependent on
the output capacitor value. The output voltage ripple is set by the internal comparator delay and the external
capacitor. The typical output voltage ripple is less than 1% of the nominal output voltage
Input Capacitor Selection
Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is
required for best input voltage filtering and minimizing the interference with other circuits caused by high input
voltage spikes. The converters need a ceramic input capacitor of 10µF. The input capacitor can be increased
without any limit for better input voltage filtering.
TYPE
DCDC Output Cap
LDO Input/Output Cap
DCDC Output Cap
DCDC Input/Output Cap
Table 2. Tested Capacitors
COMPONENT SUPPLIER
Murata
GRM155R60G475ME47D
Murata
GRM155R60J225ME15D
Murata
GRM188R60J475K
Murata
GRM188R60J106M69D
VALUE
4.7 µF
2.2 µF
4.7 µF
10 µF
VOLTAGE
RATING
4V
6.3 V
6.3 V
6.3 V
SIZE
0402
0402
0603
0603
MATERIAL
Ceramic X5R
Ceramic X5R
Ceramic X5R
Ceramic X5R
Copyright © 2010, Texas Instruments Incorporated
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