Datasheet

f
OUT
IN
RMSCout OUT
V
1 -
V
1
I = V x x
L x
2 x 3
f f
OUT
IN
OUT OUT
OUT
V
1 -
V
1
V = V x x + ESR
L x 8 x C x
D
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TPS65000, TPS65001, TPS650001
TPS650003, TPS650006, TPS650061
SLVS810B –JUNE 2009–REVISED AUGUST 2010 www.ti.com
Output Capacitor Selection
The advanced Fast Response voltage mode control scheme of the converter allows the use of small ceramic
capacitors with a typical value of 22mF, 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 therefore,
are recommended. See the recommended components.
If ceramic output capacitors are used, the capacitor RMS ripple current rating will always meet the application
requirements. The RMS ripple current is calculated as:
(8)
At nominal load current, the device operates 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:
(9)
Where the highest output voltage ripple occurs at the highest input voltage V
IN
.
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.
The adjustable output voltage of the DCDC converter is calculated by Equation 1 in the Step-Down Converter. To
keep the external resistor divider network robust against noise, an external feed forward capacitor is required for
optimum load transient response. The value of feed forward capacitor should be in the range between 22pF and
33pF provided the equivalent resistance of RDC1 || RDC2 in Equation 1 is approximately 300kΩ. Scale change
on RDC1||RDC2 would apply a scale change to the feed forward capacitor to keep the RC product a constant.
Input Capacitor Selection
Due to the nature of the DCDC 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. It is critical to put the input capacitor as close to the VINDCDC pin as close as possible with the clean
GND connection provided. The same consideration is applied for the output capacitor and the inductor. The
converters need a ceramic input capacitor of 10mF. The input capacitor can be increased without any limit for
better input voltage filtering.
Table 3. Capacitors
CAPACITANCE SUPPLIER TYPE
22mF TDK C2012X5R0J226MT Ceramic
22mF Taiyo Yuden JMK212BJ226MG Ceramic
10mF Taiyo Yuden JMK212BJ106M Ceramic
10mF TDK C2012X5R0J106M Ceramic
10mF Murata GRM188R60J106M69D Ceramic
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