Datasheet

( )
( )
(
)
( )
( )
( )
(
)
- ´ - ´
= ´ = ´
´ ´
IN OUT OUT IN OUT OUT
max max
SW IN OUT SW IN(max)
IND ripple max max
V V V V V V
1 3
L
I f V I f V
( )
( )
( )
(
)
( )
- ´
= + ´
´ ´
IN OUT OUT
max
TRIP
IND peak
SW IN
DS on max
V V V
V
1
I
8 R L f V
( )
( )
( )
( )
( )
( )
´ ´ - ´ ´
´
= = = W
´
OUT SW
SW
IND ripple
V 10 mV (1 D) 10 mV L f
L f
ESR
0.6 V I 0.6 V 60
( )
´
- -
= ´
IND ripple
OUT
I ESR
V 0.6
2
R1 R2
0.6
TPS53315
SLUSAE6 –DECEMBER 2010 www.ti.com
External Parts Selection
The external components selection is a simple process using D-CAP™ Mode.
1. CHOOSE THE INDUCTOR
The inductance value should be determined to give the ripple current of approximately 1/4 to ½ of maximum
output current. Larger ripple current increases output ripple voltage and improves signal-to-noise ratio and
helps stable operation.
(6)
The inductor requires a low DCR to achieve good efficiency. It also requires enough room above peak
inductor current before saturation. The peak inductor current can be estimated in Equation 7.
(7)
2. CHOOSE THE OUTPUT CAPACITOR(S)
When organic semiconductor capacitor(s) or specialty polymer capacitor(s) are used, for loop stability,
capacitance and ESR should satisfy Equation 2. For jitter performance, Equation 8 is a good starting point to
determine ESR.
where
• D is the duty factor
• t
SW
is the switching period
• the required output ripple slope is approximately 20 mV per t
SW
in terms of V
VFB
(8)
3. DETERMINE THE VALUE OF R1 AND R2
The output voltage is programmed by the voltage-divider resistor, R1 and R2 shown in Figure 37. R1 is
connected between VFB pin and the output, and R2 is connected between the VFB pin and GND.
Recommended R2 value is from 10kΩ to 20kΩ. Determine R1 using Equation 9.
(9)
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