AAT1235 Analogic Corporation, AAT1235 Datasheet - Page 18

• Manufacturer Part Number: AAT1235
• Manufacturer: Analogic Corporation

PCB Layout Guidelines
Boost converter performance can be adversely
affected by poor layout. Possible impact includes
high input and output voltage ripple, poor EMI per-
formance, and reduced operating efficiency. Every
attempt should be made to optimize the layout in
order to minimize parasitic PCB effects (stray resist-
ance, capacitance, and inductance) and EMI cou-
pling from the high frequency SW node. A suggest-
ed PCB layout for the AAT1235 boost converter is
shown in Figures 4 and 5. The following PCB layout
guidelines should be considered:
1. Minimize the distance from Capacitor C1 and
Output capacitor size can be estimated at a switch-
ing frequency (F
18
Manufacturer
Murata
Murata
Murata
Murata
Murata
C2’s negative terminals to the GND pins. This
is especially true with output capacitor C2,
which conducts high ripple current from the
output diode back to the GND pins.
S
C
) of 500kHz (worst case):
OUT
=
GRM21BR71E225KA73L
GRM21BR71A225KA01
GRM21BR61E475KA12
GRM219R61E225KA12
I
GRM188R60J225KE19
F
OUT
S
· ΔV
Part Number
· D
Table 10: Recommended Ceramic Capacitors.
MAX
OUT
Value (µF)
2.2
2.2
2.2
2.2
4.7
High Efficiency White LED Drivers
To maintain stable operation at full load, the output
capacitor should be selected to maintain ΔV
between 100mV and 200mV.
The boost converter input current flows during both
ON and OFF switching intervals. The input ripple
current is less than the output ripple and, as a
result, less input capacitance is required.
2. Minimize the distance between L1 to D1 and
3. Maintain a ground plane and connect to the IC
4. Consider additional PCB metal on D1’s cath-
5. Do not connect the exposed paddle (bottom of
switching pin SW; minimize the size of the PCB
area connected to the SW pin.
GND pin(s) as well as the GND connections of
C1 and C2.
ode to maximize heatsinking capability. This
may be necessary when using a diode with a
high V
the die) to either AGND or GND because it is
connected internally to SW. Connect the
exposed paddle to the SW pin or leave floating.
Voltage Rating
F
and/or thermal resistance.
for Backlight and Keypad
6.3
10
25
25
25
Temp Co
X5R
X7R
X5R
X7R
X5R
Case Size
1235.2007.01.1.0
0603
0805
0805
0805
0805
OUT