Datasheet

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APPLICATION INFORMATION
ADJUSTABLE OUTPUT VOLTAGE VERSION
V
O
 0.5 V 

1 
R1
R2

(3)
C1 
1
2    10 kHz  R1
(4)
C2 
R1
R2
 C1
(5)
VIN
VIN
EN
MODE
SW
FB
PGND
PGND
SW
GND
2
3
1
4 9
10
5
7
8
6
TPS62020
C3
22 µF
V
I
2.5 V to 6 V
L1
6.2 µH
C4
22 µF
V
O
1.8 V / 600 mA
R1
470 kΩ
R2
180 kΩ
C1
33 pF
C2
100 pF
Inductor Selection
TPS62020
TPS62021
TPS62026
SLVS076C – JUNE 2003 – REVISED DECEMBER 2004
When the adjustable output voltage version TPS6202x is used, the output voltage is set by the external resistor
divider. See Figure 15 .
The output voltage is calculated as:
with R1 + R2 ≤ 1 M Ω and internal reference voltage V
ref
typical = 0.5 V
R1 + R2 should not be greater than 1 M Ω because of stability reasons. To keep the operating quiescent current
to a minimum, the feedback resistor divider should have high impedance with R1+R2 ≤ 1 M Ω . Due to this and the
low reference voltage of V
ref
= 0.5 V, the noise on the feedback pin (FB) needs to be minimized. Using a
capacitive divider C1 and C2 across the feedback resistors minimizes the noise at the feedback, without
degrading the line or load transient performance.
C1 and C2 should be selected as:
with:
• R1 = upper resistor of voltage divider
• C1 = upper capacitor of voltage divider
For C1 a value should be chosen that comes closest to the calculated result.
with:
• R2 = lower resistor of voltage divider
• C2 = lower capacitor of voltage divider
For C2, the selected capacitor value should always be selected larger than the calculated result. For example, in
Figure 15 for C2 100 pF are selected for a calculated result of C2 = 88.42 pF.
If quiescent current is not a key design parameter C1 and C2 can be omitted, and a low impedance feedback
divider has to be used with R1 + R2 < 100 k Ω . This reduces the noise available on the feedback pin (FB) as well
but increases the overall quiescent current during operation. The higher the programmed output voltage the
lower the feedback impedance has to be for best operation when not using C1 and C2.
Figure 15. Adjustable Output Voltage Version
The TPS6202x uses typically a 10-µH output inductor. Larger or smaller inductor values can be used to optimize
the performance of the device for specific operation conditions. When changing inductor values, the product of
the inductor value times output-capacitor value (L × C) should stay constant. For example, when reducing the
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