Dual Channel 600mA Step-Down Converter
Applications Information
Setting the Output Voltage
Figure 1 shows the basic application circuit for the
AAT2514. Resistors R1 and R3 and R2 and R4
program the output to regulate at a voltage higher
than 0.6V. To limit the bias current required for the
external feedback resistor string while maintaining
good noise immunity, the minimum suggested value
for R1 and R3 is 59kΩ. Although a larger value will
further reduce quiescent current, it will also
increase the impedance of the feedback node, mak-
ing it more sensitive to external noise and interfer-
ence. Table 1 summarizes the resistor values for
various output voltages with R1 and R3 set to either
59kΩ for good noise immunity or 316kΩ for reduced
no load input current.
The adjustable feedback resistors, combined with
a external feed forward capacitors (C4 and C5 in
Figure 1), deliver enhanced transient response for
extreme pulsed load applications. The addition of
the feed forward capacitor typically requires a larg-
er output capacitor C2 and C3 for stability. The
external resistor sets the output voltage according
to the following equation:
R 2
V
OUT
= 0.6 V ·
1 +
R1
or
V
R2 =
OUT
- 1 · R1
V
REF
Ω
R1, R3 = 59kΩ
Ω
R2, R4 (kΩ)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
AAT2514
V
OUT
(V)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
Table 1: Resistor Selection for Output Voltage
Setting; Standard 1% Resistor Values
Substituted Closest to the Calculated Values.
EN1
V
IN
2.5V to 5.5V
V
OUT2
2.5V
C1
10µF
L2 2.2µH
EN2
POR
IN
R5
100kΩ
RESET
L1 2.2µH
V
OUT1
1.8V
AAT2514
LX1
LX2
C5 22pF
C3
10µF
FB2
R4
1MΩ
R3
316kΩ
GND
C4 22pF
FB1
R1
316kΩ
R2
634kΩ
C2
10µF
Figure 1: AAT2514 Typical Application Circuit.
2514.2007.06.1.0
R1, R3 = 316k
Ω
Ω
R2, R4 (kΩ)
105
158
210
261
316
365
422
475
634
655
732
1000
1430
9
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