Datasheet

0 0.5 1.0 1.5
LOAD CURRENT (A)
3.0
3.5
4.0
4.5
5.0
5.5
V
IN
(V)
V
PP-RMS
=
V
PP-C
2
+ V
PP-ESR
2
V
PP-C
=
I
RIPPLE
*
*
4 f C
LP3972
www.ti.com SNVS468K –SEPTEMBER 2006–REVISED MAY 2013
The output voltage ripple is caused by the charging and discharging of the output capacitor and also due to its
ESR and can be calculated as:
(4)
Voltage peak-to-peak ripple due to ESR can be expressed as follows
V
PP-ESR
= (2 * I
RIPPLE
) * R
ESR
(5)
Because these two components are out of phase the RMS value can be used to get an approximate value of
peak-to-peak ripple.
Voltage peak-to-peak ripple, root mean squared can be expressed as follows
(6)
Note that the output voltage ripple is dependent on the inductor current ripple and the equivalent series
resistance of the output capacitor (R
ESR
).
The R
ESR
is frequency dependent (as well as temperature dependent); make sure the value used for calculations
is at the switching frequency of the part.
Table 2. Suggested Capacitor and Their Suppliers
Model Type Vendor Voltage Case Size Inch (mm)
GRM21BR60J106K Ceramic, X5R Murata 6.3V 0805 (2012)
JMK212BJ106K Ceramic, X5R Taiyo-Yuden 6.3V 0805 (2012)
C2012X5R0J106K Ceramic, X5R TDK 6.3V 0805 (2012)
Buck Output Ripple Management
If V
IN
and I
LOAD
increase, the output ripple associated with the Buck Regulators also increases. Figure 32 shows
the safe operating area. To ensure operation in the area of concern it is recommended that the system designer
circumvents the output ripple issues to install Schottky diodes on the Buck(s) that are expected to perform under
these extreme corner conditions.
(Schottky diodes are recommended to reduce the output ripple, if system requirements include this shaded area
of operation. V
IN
> 1.5V and I
LOAD
> 1.24)
Figure 32.
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