Cirrus Logic AN372 - Manual (Page 9)

AN372
AN372REV1 9
The buck stage is supplied by the boost output voltage. The boost output voltage is regulated within 10% by
the boost stage. The buck control loop regulates the output current as long as the peak current has sufficient
margin to rise 10% at the lowest boost output voltage. Figure 4a and Figure 4b show idealized waveforms of
the FET Q4 drain voltage and drain current and the diode D3 current.
Area = N ު V
OUT
ު T2
Area = V
OUT
ު T2
Area = (V
BST
- V
OUT
) ު T1
V
BST
V
ZERO
N ު V
OUT
V
OUT
t
V
Reflected
Figure 4a. FET Drain Voltage
T1
TT
T3 '
C
1- '
C
T2
1
I
PK(FB)
t
(N+1) ު I
PK(FB)
I1
I2
Figure 4b. Current Through FET Q4 and Diode D3