o
2
1
1
C8
2
R
=
´
p
f
o
OUT
OUT
3.95
V
C
=
´
f
OUT
R2
0.596 V
R3
V
0.596 V
´
=
-
Introduction
3
SLVUAP3 – April 2016
Copyright © 2016, Texas Instruments Incorporated
TPS54202EVM-716 2-A Regulator Evaluation Module
1.3
Modifications
These evaluation modules are designed to provide access to the features of the TPS54202. Some
modifications can be made to this module.
1.3.1
Output Voltage Set Point
The voltage divider, R2 and R3, is used to set the output voltage. To change the output voltage of the
EVM, it is necessary to change the value of resistor R3. Changing the value of R3 can change the output
voltage above 0.596 V. The value of R3 for a specific output voltage can be calculated using
Use 100 k
Ω
for R2.
(1)
lists the R2 and R3 values for some common output voltages. Note that V
IN
must be in a range so
that the minimum on-time is greater than 150 ns. The values in
are standard values, not the exact
value calculated using
Table 3. Recommended Component Values
V
OUT
(V)
L (µH)
C
OUT
(µF)
R2 (k
Ω
)
R3 (k
Ω
)
C8 (pF)
1.8
5.6
66
100
49.9
47
2.5
8.2
44
100
31.6
33
3.3
10
44
100
22.1
56
5
15
44
100
13.3
75
12
22
44
100
5.23
100
1.3.2
Output Capacitor and Feed-Forward Capacitor
Considering the loop stability and the effect of the internal parasitic parameters, choose a crossover
frequency less than 40 kHz, without considering the feed-forward capacitor. A simple estimation for the
crossover frequency without feed-forward capacitor C8 is shown in
, assuming C
OUT
has small
ESR.
(2)
Depending on V
OUT
, if the output capacitor, C
OUT
, is dominated by low-ESR (ceramic types) capacitors, a
low phase margin could result. To improve the phase boost, an external feed-forward capacitor, C8, can
be added in parallel with R2. C8 is chosen such that phase margin is boosted at the crossover frequency.
C8 is calculated in
:
(3)
For this design, C8 = 75 pF. C8 is not needed when C
OUT
has high ESR, and C8 calculated from
should be reduced with medium ESR. Use
as a starting point.
