PM6685_07 Datasheet, PDF (23/52 Pages) STMicroelectronics – Dual step-down main supply controller with auxilary voltages for notebook system power

PM6685
Figure 29. Constant ON-time block diagram
Device description
Toff-min
CSENSE
+
Positive
Current Limit
-
COMP
OUT
Vr
+
- PWM
Comparator
gm
+
RFb1
Vr
RFb2
SQ
RQ
Ton
Zero-cross.
+ ^Comp.
-
VIN
SKIP
0.5V ₊
-
Level
shifter
HS
driver
+ 0.5V
-
SQ
+ 0.25V
-
LDO5
LS
driver
R
LDO5
bandgap
1.236V
Vr
BOOT
HGATE
PHASE
LGATE
PGND
VREF
7.3
Output ripple compensation
In a classic Constant On Time control, the system regulates the valley value of the output
voltage and not the average value, as shown in Figure 28 on page 21. In this condition, the
output voltage ripple is source of a DC static error.
To compensate this error, an integrator network can be introduced in the control loop, by
connecting the output voltage to the COMP5/COMP3(for the 5V and 3.3V sections
respectively) pin through a capacitor C_INT as in Figure 30 on page 24.
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