AAT1415-Q8-T AAT [Advanced Analog Technology, Inc.], AAT1415-Q8-T Datasheet - Page 31

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

Set the loop cross over frequency (
of 1/10 the switching frequency (
compensation
crossover frequency
following equation:
Where:
The
so:
The typical
If the system wants better transient response, it can
parallel a capacitor
If
omitted. Additional
So, for a –7V/50mA output with V
C
M
R
C
R
C
R
V
OUT _
U
UPPER
C
C
C
C
=
C
=
=
=
=
=
U
2
R C
R
2
140
(
R
( 7
⋅
C C
L
is calculated to be less than 10pF, it can be
LOAD
π ×
− +
V
:
LOAD
2 2.2nF
= 56 kΩ ,
⋅
OUT
⋅
f
Ω ⋅
SW
2
R
⋅
UPPER _
R
1.25V)
10 µ F
C
zero is then used to cancel the
⋅
+
C
C
C
V
V
3V
OUT
capacitor
I
is under 500 kΩ .
REF
f
≈
SW
⋅
C can suppress the inrush current.
×
300k
)
U
f . Determine the value by the
⋅
f
33.6m
C
C with
C
= 500kHz:
U
1
M
×
Ω




×
V
C
,
2
×
OUT _
C
G
⋅ π
2
R
70 µ A / V
m
π ⋅
Advanced Analog Technology, Inc.
V
f
to
UPPER _
C
IN _
I
20kHz
+
f ) below the lower
= 3.0V, L = 4.7µH,
f
C
SW
set
V
IN _
). Choose the
–
from IN_ to
≈
the




2.2nF
–
Advanced Analog Technology, Inc . –
台 灣 類 比 科 技 股 份 有 限 公 司
f
P
desired
pole,
Page 31 of 32
Version 3.00
LAYOUT CONSIDERATIONS
Conductors carrying discontinuous currents and any
high-current path should be made as short and wide as
possible. The compensation network should be very
close to the EO_ pin and avoid through VIA. The IC
must be bypassed with ceramic capacitors placed
close to the VDD and VREF. A separate low-noise
ground plane containing the reference and signal
grounds should connect to the power-ground plane at
only one point to minimize the effects of power-ground
currents. Typically, the ground planes are best joined
right at the IC. Tie the feedback resistor divider to be
very close to output capacitor and far away from the
inductor or Schottky diode. Keep the feedback network
(IN_) close to the IC. Switching nodes (SW_) should be
kept as small as possible and should be routed away
from high-impedance nodes such as IN.
C
U
=
2
π ×
–
56k
Ω ×
20kHz
AAT1415/AAT1415A
1
×




V
OUT _
V
IN _
+
V
IN _




≈
1nF
May 2008