AAT1415-Q8-T AAT [Advanced Analog Technology, Inc.], AAT1415-Q8-T Datasheet - Page 26

• Manufacturer Part Number: AAT1415-Q8-T
• Description: FIVE-CHANNEL DC-DC CONVERTER WITH A 2.5V LDO
• Manufacturer: AAT [Advanced Analog Technology, Inc.]

DESIGN PROCEDURE
Programming the Output Voltage
The output voltage for each channel is programmed
using a resistor divider from the output connected to
the feedback pins. When setting the output voltage,
connect a resistive voltage divider from the channel
output to the corresponding IN_ input and then to GND.
Choose the lower-side (IN_-to-GND) resistor, then
calculate the upper-side (output-to-IN_) resistor as
follows:
Where
(AAT1415/AAT1415A,
for
R
R
UPPER _
UPPER _
Figure 9a. Feedback Network (For Boost/Buck)
R
Figure 9b. Feedback Network (For Inverting)
LOWER _
V
IN_
=
=
R
R
LOWER _
LOWER _
is the feedback regulation voltage, 1.250V
are in the range of 10 k Ω to 100 k Ω .








V
V
−
IN3
OUT _
V
V
V
IN_
OUT _
REF
= 0.8V ), and typical values
−




1
Advanced Analog Technology, Inc.




(For Inverting),
(For Boost / buck),
–
–
Advanced Analog Technology, Inc . –
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Page 26 of 32
Version 3.00
Inductor Selection
The inductor is typically selected to operate with
continuous conduction mode (CCM) for best efficiency
in
conduction mode (DCM) for better response ability in
boost or inverting controller (Table 1 and Table 2). The
recommended inductance value range is between
2.2µH and 4.7µH for boost. The recommended
inductance value range is between 6.8µH and 22µH for
buck. The recommended inductance value range is
between 3.3µH and 6.8µH for Inverting. With the
chosen inductance value, the peak current for the
inductor in steady state operation can be calculated
(Table 3). It also needs to be taken into account that
load transients and error conditions may cause higher
inductor currents. This also needs to be taken into
account when selecting an appropriate inductor.
Topology
Inductance Unit: Henry
L : Inductance, Response Ability Unit:
R
V : Input Voltage,
V : Input Voltage,
Inverting
Table 1. Response Ability for Various Topologies
Topology
IN
IN
LOAD
Boost
Inverting
Boost or
Buck
Table 2. DCM/CCM Critical Inductance Values
boost
Buck
: Loading,
–
or
V
1
OUT
−
buck
V
V
V
f
OUT
OUT
V
SW
D
IN
V
OUT
V
AAT1415/AAT1415A
+ V
IN
V
OUT
: Switch Frequency,
OUT
IN
converter
: Output Voltage,
: Output Voltage,
Response Ability
V
IN
R
−
V
R
LOAD
L
L
(1 D) R
IN
V
and
LOAD
DCM/CCM
OUT
−
mA
µs
2 f
2 f
2 f
⋅ ⋅ −
⋅
⋅
⋅
D (1 D)
⋅
⋅
discontinuous
SW
SW
SW
(1 D)
LOAD
−
May 2008
2
2