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TPS65167 View Datasheet(PDF) - Texas Instruments

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TPS65167 Compact LCD Bias Supply for TFT-LCD TV Panels TI
Texas Instruments TI
TPS65167 Datasheet PDF : 42 Pages
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TPS65167
TPS65167A
www.ti.com
SLVS760C – APRIL 2007 – REVISED MARCH 2008
Selecting the Feed-forward Capacitor (step-down converter)
The feed-forward capacitor across the upper feedback resistor divider form a zero around 170 kHz and is
calculated as:
C17 =
1
=
1
= 468 pF = 470 pF
2 x p x 170kHz x R9 2 x p x 170kHz x 2k
(8)
The capacitor value closest to the calculated value is selected.
Inductor Selection (step-down converter)
The TPS65167 operates typically with a 10-µH inductor value. For high efficiencies, the inductor should have a
low dc resistance to minimize conduction losses. This needs to be considered when selecting the appropriate
inductor. To avoid saturation of the inductor, the inductor should be rated at least for the maximum output current
of the converter plus the inductor ripple current that will be calculated as:
DIL + Vout
1
*
Vout
Vin
Lƒ
ILmax
+
Ioutmax
)
DIL
2
(9)
With:
f = Switching Frequency (750 kHz)
L = Inductor Value (typically 10 µH)
ΔIL= Peak to Peak inductor ripple current
ILax = Maximum Inductor current
The highest inductor current occurs at maximum Vin. A more conservative approach is to select the inductor
current rating just for the minimum switch current limit of 2.8 A.
INDUCTOR VALUE
10 µH
10 µH
10 µH
Table 8. Inductor Selection (Step down converter)
COMPONENT SUPPLIER
Sumida CDRH8D43-100
Wuerth 744066100
Coilcraft DO3316P-103
DIMENSIONS in mm
8.3 × 8.3 × 4.5
10 × 10 × 3.8
12.95 × 9.4 × 5.51
Sat/DCR
4 A/29 m
4 A/25 m
3.9 A/38 m
Rectifier Diode Selection (step-down converter)
To achieve high efficiency, a Schottky diode should be used. The reverse voltage rating should be higher than
the maximum output voltage of the step-down converter. The averaged rectified forward current that the Schottky
diode must be rated is calculated as the off time of the step-down converter times the minimum switch current of
the TPS65167:
D
+
Vout
Vin
(10)
Iavg + (1 * D)
Isw
+
1
*
Vout
Vin
2.8 A
with Isw = minimum switch current of the TPS65167 (2.8 A)
A Schottky diode with 2 A maximum average rectified forward current rating is sufficient for most of the
applications. The Schottky rectifier has to be able to dissipate the power. The dissipated power is the average
rectified forward current times the diode forward voltage.
PD + Iavg VF + Isw (1 * D) VF with Isw = minimum switch current of the TPS65167 (2.8 A)
CURRENT RATING Avg.
3A
2A
2A
Table 9. Rectifier Diode Selection step-down Converter
Or
Vforward
20V
0.36 at 3A
20V
0.44V at 2A
20V
0.5 at 2A
RθJA
46°C/W
75°C/W
75°C/W
SIZE
S.C.
SMB
SMB
COMPONENT SUPPLIER
MBRS320, International Rectifier
SL22, Vishay Semiconductor
SS22, Fairchild Semiconductor
Copyright © 2007–2008, Texas Instruments Incorporated
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