Datasheet
( )
300000
Fm
TPS55383
5
5.6 10 t
V V
ON
6
IN OUT
19.7 e 50 10
L
=
é ù
´ ´
-
æ ö
ê ú
-
´ + ´ ´
ç ÷
ê ú
ç ÷
è ø
ê ú
ë û
(6)
4
V Fm 2 10
IN
fc
6
V Fm 50 10
IN
1
R
LOAD
-
´ ´ ´
=
´ ´ ´
+
æ æ öö
ç ç ÷÷
ç ç ÷÷
è è øø
(7)
EA
CO LOAD OUT
fc
K 20 log
1 2 f R C
æ ö
= - ´
ç ÷
+ p´ ´ ´
è ø
(8)
1
2
3
4
16
15
14
13
PVDD2
BOOT2
SW2
BP
PVDD1
BOOT1
SW1
GND
TPS5538x
5
6
7
12
11
10
SEQ
ILIM2
FB2
EN1
EN2
FB1
L
C
OUT
R1
Output1
R2
C2
(optional)
UDG-08042
8 9COMP2COMP1
R
COMP
C
COMP
C1
(optional)
Z
UPPER
Z
LOWER
L C
OUT
C1
R1
´
=
(9)
TPS55383 , , TPS55386
SLUS818 – SEPTEMBER 2008 .........................................................................................................................................................................................
www.ti.com
The overall DC gain of the of the converter control-to-output transfer function is approximated by:
The next step is to find the desired gain of the error amplifier at the desired crossover frequency. Assuming a
single pole roll off, evaluate the following expression at the desired crossover frequency.
Figure 24. Loop Compensation Components
If operating at wide duty cycles (over 50%), a capacitor may be necessary across the upper resistor of the
voltage setting divider. (Ref Figure 24 ) If duty cycles are less than 50%, this capacitor may be omitted.
If a high ESR capacitor is used in the output filter, a zero appears in the loop response that could lead to
instability. To compensate, a small capacitor is placed in parallel with the lower voltage setting divider resistor
(Ref Figure 24 ). The value of the capacitor is determined such that a pole is placed at the same frequency as the
ESR zero. If low ESR capacitors are used, this capacitor may be omitted.
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