Datasheet

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TPS62110-HT
www.ti.com SLVSAO9B –DECEMBER 2010– REVISED FEBRUARY 2011
(4)
The overall output ripple voltage is the sum of the voltage spike caused by the output capacitor ESR plus the
voltage ripple caused by charge and discharging the output capacitor:
(5)
Where the highest output voltage ripple occurs at the highest input voltage V
I
.
INPUT CAPACITOR SELECTION
The nature of the buck converter is a pulsating input current; therefore, 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 input capacitor should have a minimum value of 10 µF and can be increased without any limit for
better input voltage filtering. The input capacitor should be rated for the maximum input ripple current calculated
as:
(6)
The worst-case RMS ripple current occurs at D = 0.5 and is calculated as: I
RMS
= I
O
/2. Ceramic capacitors show
a good performance because of their low ESR value, and they are less sensitive against voltage transients
compared to tantalum capacitors. Place the input capacitor as close as possible to the input pin of the IC for best
performance
FEEDFORWARD CAPACITOR SELECTION
The feedforward capacitor (C
ff
) is needed to compensate for parasitic capacitance from the feedback pin to GND.
Typically, a value of 4.7 pF to 22 pF is needed for an output voltage divider with a equivalent resistance (R1 in
parallel with R2) in the 150 kΩ range. The value can be chosen based on best transient performance and lowest
output voltage ripple in PFM mode.
RECOMMENDED CAPACITORS
It is recommended that only X5R or X7R ceramic capacitors be used as input/output capacitors. Ceramic
capacitors show a dc-bias effect. This effect reduces the effective capacitance when a dc-bias voltage is applied
across a ceramic capacitor, as on the output and input capacitor of a dc/dc converter. The effect may lead to a
significant capacitance drop especially for high input/output voltages and small capacitor packages. See the
manufacturer's data sheet about the performance with a dc bias voltage applied. It may be necessary to choose
a higher voltage rating or nominal capacitance value to get the required value at the operating point. The
capacitors listed in Table 3 have been tested with the TPS62110 with good performance.
Table 3. List of Capacitors
(1)(2)
MANUFACTURER PART NUMBER SIZE VOLTAGE CAPACITANCE TYPE
TMK316BJ106KL 1206 25 V 10 µF
Taiyo Yuden Ceramic
EMK325BJ226KM 1210 16 V 22 µF
C3225X5R1E106M 25 V 10 µF
1210
TDK C3225X7R1C226M 16 V 22 µF Ceramic
C3216X5R1E106MT 1206 25 V 10 µF
(1) Component selections are for 25°C only and will change for new temperature range.
(2) Components have not been validated for extreme high temperature operation.
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