Datasheet
( )
( )
( ) ( )
( ) ( )
4 3 4
IN m
1
6 3 6
IN
LOAD1
V F 2 10 13.2 5.82 10 2 10
fc 4.63
V Fm 50 10 13.2 5.82 10 50 10
1 1
R 1.67
- -
- -
´ ´ ´ ´ ´ ´ ´
= = =
æ ö æ ö
´ ´ ´ ´ ´ ´ ´
ç ÷ ç ÷
+ +
ç ÷ ç ÷
W
è ø è ø
(47)
1
EA1
CO LOAD1 OUT1
fc
4.65
K 20 log 20 log 5.80 dB
1 2 f R C 1 2 35 kHz 1.67 22 F
æ ö
æ ö
= - ´ = - ´ =
ç ÷
ç ÷
+ p ´ ´ ´ + p ´ ´ W ´ m
è ø
è ø
(48)
( ) ( )
EA
K
5.80 dB
20
20
LOWER UPPER
COMP1
M LOWER
10 Z Z
10 3.83k 20.5k
R 38.5k R15 38.3k
g Z 315 S 3.83k
´ +
´ W + W
= = = W Þ = W
´ m ´ W
(49)
ZERO1
OUT1 LOAD1
1 1
f 4.4kHz
2 C R 2 22 F 1.67
= = =
p´ ´ p ´ m ´ W
(50)
COMP1
POLE1 COMP1
1 1
C 967pF C21 1nF
2 f R 2 4.4kHz 3.83k
= = = Þ =
p´ ´ p´ ´ W
(51)
HF1
CO COMP
1 1
C 29.6pF C23 33pF
2 4 f R 2 4 35kHz 38.3k
= = = Þ =
p´ ´ ´ p ´ ´ ´ W
(52)
TPS55383 , , TPS55386
SLUS818 – SEPTEMBER 2008 .........................................................................................................................................................................................
www.ti.com
Then calculate the converter gain at DC:
Calculate the required error amplifier gain at the desired crossover frequency of 35 kHz:
Then compensation resistor at the output of the error amplifier is:
Calculate the required compensation zero frequency:
Then calculate the compensation capacitor:
The high-frequency pole is placed at eight times the crossover frequency:
Boot-Strap Capacitor
To ensure proper charging of the high-side FET gate and limit the ripple voltage on the boost capacitor, a 47-nF
boot strap capacitor is used.
ILIM2
The current limit must be set above the peak inductor current I
Lpeak
. Comparing I
Lpeak
to the available minimum
current limits, I
LIM
is connected to BP for a 3.6-A minimum current limit.
SEQ
The SEQ pin is left floating, leaving the enable pins to function independently. If the enable pins are tied
together, the two supplies start-up ratio-metrically. SEQ could also be connected to BP or GND to provide
sequential start-up.
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