lm26480sqx-bf National Semiconductor Corporation, lm26480sqx-bf Datasheet - Page 23

• Manufacturer Part Number: lm26480sqx-bf
• Description: Lm26480 Externally Programmable Dual High-current Step-down Dc/dc And Dual Linear Regulators
• Manufacturer: National Semiconductor Corporation

INPUT CAPACITOR SELECTION FOR SW1 AND SW2
It is required to use a ceramic input capacitor of at least 4.7
μF and 6.3V with an ESR of under 10 mΩ.
The input power source supplies average current continu-
ously. During the PFET switch on-time, however, the de-
manded di/dt is higher than can be typically supplied by the
input power source. This delta is supplied by the input capac-
itor.
A simplified “worst case” assumption is that all of the PFET
current is supplied by the input capacitor. This will result in
conservative estimates of input ripple voltage and capacitor
RMS current. Input ripple voltage is estimated as follows:
4.7 µF for CIN
10 µF for COUT
GRM21BR60J475K
GRM21BR60J106K
C2012X5R0J475K
C1608X5R0J475K
C2012X5R0J106K
C1608X5R0J106K
JMK212BJ475K
JMK212BJ106K
Model
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Type
Taiyo-Yuden
Taiyo-Yuden
23
Vendor
Murata
Murata
TDK
TDK
TDK
TDK
V
I
C
ESR
This capacitor is exposed to significant RMS current, so it is
important to select a capacitor with an adequate RMS current
rating. Capacitor RMS current estimated as follows:
I
OUT
RSCIN
PPIN
IN:
:
IN:
:
Estimated input capacitor RMS current
Estimated peak-to-peak input ripple voltage
Output current, Amps
Input capacitor value, Farads
Input capacitor ESR, Ohms
Voltage Rating
6.3V
6.3V
6.3V
6.3V
6.3V
6.3V
6.3V
6.3V
0805, (2012)
0805, (2012)
0805, (2012)
0603, (1608)
0805, (2012)
0805, (2012)
0805, (2012)
0603, (1608)
Case Size
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