Datasheet

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APPLICATION INFORMATION
ADJUSTABLE OUTPUT VOLTAGE VERSION
V
out
+ 0.5 V
ǒ
1 )
R1
R2
Ǔ
C1 +
1
2 p 10 kHz R1
C2 +
R1
R2
C1
V
I
GND
EN
SW
FB
C3
4.7 µF
L1
10 µH
C4
10 µF
TPS62200
V
I
2.5 V − 6 V
V
O
1.8 V / 300 mA
R1
470k
R2
180k
C1
33 pF
C2
100 pF
INDUCTOR SELECTION
TPS62200 , , TPS62201
TPS62202 , TPS62203 , TPS62207
TPS62204 , TPS62205 , TPS62208
SLVS417E – MARCH 2002 – REVISED MAY 2006
When the adjustable output voltage version TPS62200 is used, the output voltage is set by the external resistor
divider. See Figure 16 .
The output voltage is calculated as
• R1 + R2 ≤ 1 M Ω and internal reference voltage V(ref)typ = 0.5 V
R1 + R2 should not be greater than 1 M Ω for reasons of stability. To keep the operating quiescent current to a
minimum, the feedback resistor divider should have high impedance with R1+R2 ≤ 1 M Ω . Because of the high
impedance 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
• 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.
• 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 16 for C2, 100 pF are selected for a calculated result of C2 = 86.17 pF.
If quiescent current is not a key design parameter, C1 and C2 can be omitted, and a low-impedance feedback
divider must be used with R1+R2 <100 k Ω . This design reduces the noise available on the feedback pin (FB) as
well, but increases the overall quiescent current during operation.
Figure 16. Typical Application Circuit for the Adjustable Output Voltage
The TPS6220x device is optimized to operate with a typical inductor value of 10 µH.
For high efficiencies, the inductor should have a low dc resistance to minimize conduction losses. Although the
inductor core material has less effect on efficiency than its dc resistance, an appropriate inductor core material
must be used.
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