AAT2514_08 ANALOGICTECH [Advanced Analogic Technologies], AAT2514_08 Datasheet - Page 9

• Manufacturer Part Number: AAT2514_08
• Description: Dual Channel 600mA Step-Down Converter
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

SwitchReg
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 feed-
back node, making it more sensitive to external noise
and interference. 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 larger output capacitor C2
and C3 for stability. The external resistor sets the output
voltage according to the following equation:
2514.2008.02.1.1
TM
V
or
R2 =
OUT
V
V
OUT2
IN
=
⎡
⎣
2.5V to 5.5V
⎛
⎜
⎝
0
V
V
2.5V
6 .
OUT
REF
V ·
⎞
⎟
⎠
⎛
⎜
⎝
- 1
1 +
⎣
⎡
Figure 1: AAT2514 Typical Application Circuit.
· R1
10μF
R
R
C1
10μF
C3
1
2
⎞
⎟
⎠
L2 2.2μH
1MΩ
C5 22pF
R4
w w w . a n a l o g i c t e c h . c o m
R3
316kΩ
EN1
EN2
LX2
FB2
IN
AAT2514
Dual Channel 600mA Step-Down Converter
GND
Inductor Selection
For most designs, the AAT2514 operates with inductor
values of 1μH to 4.7μH. Low inductance values are
physically smaller, but require faster switching, which
results in some efficiency loss. The inductor value can be
derived from the following equation:
Where ΔI
tors lower ripple current and small value inductors result
in high ripple currents. Choose inductor ripple current
approximately 35% of the maximum load current 600mA,
or ΔI
Voltage Setting; Standard 1% Resistor Values
Substituted Closest to the Calculated Values.
V
POR
1.85
(V)
LX1
FB1
316kΩ
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
2.0
2.5
3.3
OUT
L
R1
Table 1: Resistor Selection for Output
= 210mA.
L
is inductor ripple current. Large value induc-
L1 2.2μH
C4 22pF
100kΩ
R1, R3 = 59kΩ
R2
634kΩ
R5
R2, R4 (kΩ)
RESET
L =
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
PRODUCT DATASHEET
C2
10μF
V
OUT
V
IN
· (V
· ΔI
V
OUT1
IN
L
AAT2514
· f
- V
1.8V
OSC
OUT
R1, R3 = 316kΩ
)
R2, R4 (kΩ)
1000
1430
105
158
210
261
316
365
422
475
634
655
732
9