Datasheet
R2 +
R1 1.221
V
OUT
* 1.221
(12)
+
10V-21V
L1
27 Hm
GND
VSNS
NC
NC
ENA
BOOT
PH
D1
B340A
C2
0.01 Fm
R2
3.24kW
R1
10kW
VIN
C1
10 Fm
U1
TPS5420D
TP5
5V
7
1
5
8
2
4
3
6
VOUT
VIN
ENA
C3
100 Fm
(SeeNote A)
TPS5420-Q1
SLVS752B – NOVEMBER 2007 – REVISED JUNE 2008 ...................................................................................................................................................
www.ti.com
Output Voltage Setpoint
The output voltage of the TPS5420 is set by a resistor divider (R1 and R2) from the output to the VSENSE pin.
Calculate the R2 resistor value for the output voltage of 5 V using Equation 12 :
For any TPS5420 design, start with an R1 value of 10 k Ω . R2 is then 3.24 k Ω .
Boot Capacitor
The boot capacitor should be 0.01 µ F.
Catch Diode
The TPS5420 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 one-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; therefore, the diode
parameters improve the 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
Figure 12 shows an application circuit using a wide input voltage range. 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.
A. C3 = Tantalum AVX TPSD107M010R0080
Figure 12. 10-V to 21-V Input to 5-V Output Application Circuit
Circuit Using Ceramic Output Filter Capacitors
Figure 13 shows an application circuit using all ceramic capacitors for the input and output filters that 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.
14 Submit Documentation Feedback Copyright © 2007 – 2008, Texas Instruments Incorporated
Product Folder Link(s): TPS5420-Q1