A7330
DC-DC CONVERTER BUCK (STEP-DOWN)
SENSORLESS CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
External High Voltage Bias Diode
It is recommended that an external High Voltage Bias diode be added when the system has a 5V fixed input
or the power supply generates a 5V output. This helps improve the efficiency of the regulator. The High
Voltage Bias diode can be a low cost one such as IN4148 or BAT54, as figure shown below.
This diode is also recommended for high duty cycle operation and high output voltage applications.
Input Capacitor
The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the
converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor
during switching, its ESR also affects efficiency.
The input capacitance needs to be higher than 10μF.The best choice is the ceramic type, however, low ESR
tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50%
of the output current. The input capacitor should be placed close to the IN and G pins of the IC, with the
shortest traces possible. In the case of tantalum or electrolytic types, they can be further away if a small
parallel 0.1μF ceramic capacitor is placed right next to the IC.
Output Capacitor
The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage
is:
V
IN
VRIPPLE = IOUTMAX x KRIPPLE x RESR
+
28 x ∫SW2 LC OUT
Where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output
capacitor, fSW is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the
case of ceramic output capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower
capacitance value can be used for ceramic type. In the case of tantalum or electrolytic capacitors, the ripple is
dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have
sufficiently low ESR.
For ceramic output capacitor, typically choose a capacitance of about 22μF. For tantalum or electrolytic
REV1.0
- JAN 2016 RELEASED -
- 9 -
AITSEMI [ AiT Semiconductor ]
