Datasheet

Fz1=0.7xF
LC
Fp1=500000x
V
O
F
LC
F =
LC
1
2 Lp
O O
xC (EFF)Ö
C (MIN)
O
³
1
2
(2 x7000)xLp
O
VIN10 24V-
C1
4.7 Fm
L1
15 Hm
R1
10kW
R2
5.9kW
R3
549 W
C6
1500pF
U1
TPS5430DDA
VIN
GND
VSNS
PH
BOOT
PwPd
EN
3.3V
VOUT
C2
0.01 Fm
D1
MRBS340
C3
100 Fm
C7
0.1 Fm
C4
150pF
VIN
7
1
2
4
5
8
3
6
9
ENA
NC
NC
TPS5430
TPS5431
www.ti.com SLVS632E –JANUARY 2006–REVISED SEPTEMBER 2013
Figure 14. Ceramic Output Filter Capacitors Circuit
Output Filter Component Selection
Using Equation 11, the minimum inductor value is 12 μH. A value of 15 μH is chosen for this design.
When using ceramic output filer capacitors, the recommended LC resonant frequency should be no more than
7 kHz. Since the output inductor is already selected at 15 μH, this limits the minimum output capacitor value to:
(13)
The minimum capacitor value is calculated to be 34μF. For this circuit a larger value of capacitor yields better
transient response. A single 100-μF output capacitor is used for C3. It is important to note that the actual
capacitance of ceramic capacitors decreases with applied voltage. In this example, the output voltage is set to
3.3 V, minimizing this effect.
External Compensation Network
When using ceramic output capacitors, additional circuitry is required to stabilize the closed loop system. For this
circuit, the external components are R3, C4, C6, and C7. To determine the value of these components, first
calculate the LC resonant frequency of the output filter:
(14)
For this example the effective resonant frequency is calculated as 4109 Hz
The network composed of R1, R2, R3, C5, C6, and C7 has two poles and two zeros that are used to tailor the
overall response of the feedback network to accommodate the use of the ceramic output capacitors. The pole
and zero locations are given by the following equations:
(15)
(16)
Copyright © 2006–2013, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: TPS5430 TPS5431