Datasheet
C
OUT(min)
+
ǒ
I
TRAN(max)
Ǔ
2
L
V
OUT
V
OVER
V
UNDER
t
I
TRAN
C
OUT
DT +
I
TRAN
C
OUT
I
TRAN
L
V
IN
* V
OUT
+
ǒ
I
TRAN
Ǔ
2
L
ǒ
V
IN
* V
OUT
Ǔ
C
OUT
V
OVER
t
I
TRAN
C
OUT
DT +
I
TRAN
C
OUT
I
TRAN
L
V
OUT
+
ǒ
I
TRAN
Ǔ
2
L
V
OUT
C
OUT
I
L(rms)
+
ǒ
I
L(avg)
Ǔ
2
)
1
12
ǒ
I
RIPPLE
Ǔ
2
Ǹ
+
ǒ
I
OUT
Ǔ
2
)
1
12
ǒ
I
RIPPLE
Ǔ
2
Ǹ
L [
V
IN(max)
* V
OUT
0.3 I
OUT
V
OUT
V
IN(max)
1
f
SW
TPS40192, TPS40193
SLUS719E –MARCH 2007–REVISED MAY 2013
www.ti.com
• Connect signal ground island to PowerPad with a single 10-mil wide trace.
• Connect power ground to the source of the synchronous rectifier.
• The PowerPad serves as the only ground for the controller.
• PowerPAD must be connected to signal ground and power ground.
Design Procedure
Selecting the Switching Frequency
For this design the TPS40192, with f
SW
= 600 kHz, is selected to reduce inductor and capacitor sizes.
Inductor Selection
The inductor is typically sized for approximately 30% peak-to-peak ripple current (I
RIPPLE
). Given this target ripple
current, the required inductor size can be calculated by Equation 6.
Solving this for
• V
IN(max)
= 14 V
• V
OUT
= 1.8 V
• I
OUT
= 10A
• f
SW
= 600 kHz (6)
an inductor value of 0.87 μH is obtained.
A standard value of 1.0 μH is selected. Solving for I
RIPPLE
with 1.0 μH results in 2.6-A peak-to-peak ripple.
The RMS current through the inductor is approximated by Equation 7.
(7)
Using Equation 7, the maximum RMS current in the inductor is approximately 10.03 A
Output Capacitor Selection (C8)
The selection of the output capacitor is typically driven by the output transient response. The Equation 8 and
Equation 9 overestimate the voltage deviation to account for delays in the loop bandwidth and can be used to
determine the required output capacitance.
(8)
If
• V
IN(min)
> 2 × V
OUT
, use overshoot to calculate minimum output capacitance.
• V
IN(min)
< 2 × V
OUT
, use undershoot to calculate minimum output capacitance. (9)
(10)
Based on a 4-A load transient with a maximum 50 mV overshoot at 8.0 V input, calculate a minimum 178-μF
output capacitance.
With a minimum capacitance, the maximum allowable ESR is determined by the maximum ripple voltage and is
approximated by Equation 11.
20 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated
Product Folder Links: TPS40192 TPS40193