A7330
DC-DC CONVERTER BUCK (STEP-DOWN)
SENSORLESS CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP
:
2πVOUTCOUT∫SW
10GEAGCOMP x 0.8V
RCOMP
=
=5.17 x 107VOUTCOUT………… (Ω)
STEP 2. Set the zero fZ1 at 1/4 of the cross over frequency. If RCOMP is less than 15kΩ, the equation for CCOMP
is:
2.83 x105
CCOPM
=
……………….(F)
RCOMP
If RCOMP is limited to 15kΩ, then the actual cross over frequency is 6.58 / (VOUTCOUT). Therefore:
COMP = 6.45 x 10-6VOUTCOUT………(F)
C
STEP 3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the cross over
frequency, an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is:
1.77x10−6
OUT
RESRCOUT
≥
Min
,0.06 x V
………… (Ω)
COUT
And the proper value for CCOMP2 is:
C
OUT
R
COMP
ESRCOUT
CCOMP2
=
R
Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such
as 100pF may improve stability against PCB layout parasitic effects.
CC Loop Stability
The constant-current control loop is internally compensated over the 2000mA-3500mA output range. No
additional external compensation is required to stabilize the CC current.
Output Cable Resistance Compensation
To compensate for resistive voltage drop across the charger's output cable, the A7330 integrates a simple,
user-programmable cable voltage drop compensation using the impedance at the FB pin. Use the curve in
Figure 1 to choose the proper feedback resistance values for cable compensation. RFB1 is the high side
resistor of voltage divider.
REV1.0
- JAN 2016 RELEASED -
- 11 -
AITSEMI [ AiT Semiconductor ]
