A7525
AiT Semiconductor Inc.
www.ait-ic.com
DC-DC CONVERTER BOOST(STEP-UP)
1.2MHz, MICROPOWER SYNCHRONOUS
Table2. Typical Surface Mount Inductors
Max DCR (mΩ) Rated D.C. Current (A)
108.7
Part Number
Sumida
L(μH)
Size WxLxH (mm)
4.3x4.8x3.5
4.7
10
1.15
1.04
1.32
1.17
1.12
1.00
1.87
1.51
1.33
CR43
182
72
4.7
5.6
6.8
10
Sumida
101
109
128
45
5.0x5.0x3.0
5.0x5.0x3.0
CDRH4D28
4.7
6.8
10
Toko
68
D53LC
90
Output Capacitor Selection: The output capacitor is required to keep the output voltage ripple small and to
ensure regulation loop stability. A 2.2μF to 10μF output capacitor is sufficient for most applications. If output
capacitor is larger than 10μF, a phase lead capacitor must be included to maintain enough phase margin. The
output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R
dielectrics are recommended due to their low ESR and high ripple current ratings
Input Capacitor Selection: The input capacitor reduces the surge current drawn from the input and switching
noise from the device. A minimum 4.7μF input capacitor is needed for most applications. The input capacitor
impedance at the switching frequency should be less than input source impedance to prevent high frequency
switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be
used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and
small temperature coefficients.
Output Diode Selection: An Shottky diode should be included when the output voltage is above 4.5V. The
Schottky diode is optional for the output voltage not more than 4.5V, but can improve efficiency by about 2%
to 3%.
PCB Layout Guidance
The A7525 operates at 1.2MHz typically. This is a considerably high frequency for DC-DC converters. In such
case PCB layout is important to guarantee satisfactory performance. It is recommended to make traces of the
power loop, especially where switching node is involved as short and wide as possible. First of all, the
inductor, input and output capacitor should be close to the device. Feedback and shut down circuit should
avoid the proximity of large AC signals, e.g. the power inductor and switching nodes. The optional rectifier
diode (D1) can improve efficiency and alleviate the stress on the integrated MOSFET. The diode should also
REV1.1
- JAN 2012 RELEASED, SEP 2017 UPDATED -
- 10 -
AITSEMI [ AiT Semiconductor ]
