SLVS632E – JANUARY 2006 – REVISED SEPTEMBER 2013
Catch Diode
The TPS5430 is designed to operate using an external catch diode between PH and GND. The selected diode
must meet the absolute maximum ratings for the application: Reverse voltage must be higher than the maximum
voltage at the PH pin, which is VINMAX + 0.5 V. Peak current must be greater than IOUTMAX plus on half the
peak to peak inductor current. Forward voltage drop should be small for higher efficiencies. It is important to note
that the catch diode conduction time is typically longer than the high-side FET on time, so attention paid to diode
parameters can make a marked improvement in overall efficiency. Additionally, check that the device chosen is
capable of dissipating the power losses. For this design, a Diodes, Inc. B340A is chosen, with a reverse voltage
of 40 V, forward current of 3 A, and a forward voltage drop of 0.5 V.
Additional Circuits
and
show application circuits using wide input voltage ranges. The design parameters are
similar to those given for the design example, with a larger value output inductor and a lower closed loop
crossover frequency.
10-35 V
VIN
C1
4.7
m
F
ENA
C4
4.7
m
F
U1
TPS5430DDA
VIN
BOOT
ENA
PH
NC
NC
VSNS
GND
PwPd
C2
0.01
m
F
L1
22
m
H
5V
VOUT
+
D1
B340A
C3
220
m
F
R1
10 kW
C3 = Sanyo POSCAP 10TP220M
R2
3.24 kW
Figure 12. 10–35 V Input to 5 V Output Application Circuit
9-21 V
VIN
ENA
C1
U1
TPS5431DDA
VIN
BOOT
ENA
PH
NC
NC
VSNS
GND
PwPd
C2
0.01
m
F
L1
18
m
H
5V
VOUT
+
D1
B340A
C3
220
m
F
R1
10 kW
C3 = Sanyo POSCAP 10TP220M
R2
3.24 kW
Figure 13. 9–21 V Input to 5 V Output Application Circuit
Circuit Using Ceramic Output Filter Capacitors
shows an application circuit using all ceramic capacitors for the input and output filters which generates
a 3.3-V output from a 10-V to 24-V input. The design procedure is similar to those given for the design example,
except for the selection of the output filter capacitor values and the design of the additional compensation
components required to stabilize the circuit.
16
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