FDMF6820C Fairchild Semiconductor, FDMF6820C Datasheet - Page 14

• Manufacturer Part Number: FDMF6820C
• Manufacturer: Fairchild Semiconductor

© 2011 Fairchild Semiconductor Corporation
FDMF6820C • Rev. 1.0.2
Skip Mode (SMOD#)
The Skip Mode function allows for higher converter
efficiency when operated in light-load conditions. When
SMOD# is pulled LOW, the low-side MOSFET gate
signal is disabled (held LOW), preventing discharge of
the output capacitors as the filter inductor current
attempts reverse current flow – known as “Diode
Emulation” Mode.
Table 2.
Note:
4.
SMOD#
PWM
GH
VSWH
to
VSWH
GL
The SMOD# feature is intended to have a short propagation delay between the SMOD# signal and the low-side FET V
response time to control diode emulation on a cycle-by-cycle basis.
V
IH_PWM
DISB#
t
0
1
1
1
1
1
PD_PHGLL
SMOD# Logic
t
D_DEADON
1.0V
90%
t
PD_PLGHL
t
V
D_DEADOFF
90%
10%
IL_PWM
2.2V
3-State
PWM
10%
X
0
1
0
1
CCM
Figure 28.
SMOD#
SMOD# Timing Diagram
Delay from SMOD# going
LOW to LS V
X
X
0
0
1
1
14
t
PD_SLGLL
When the SMOD# pin is pulled HIGH, the synchronous
buck converter works in Synchronous Mode. This mode
allows for gating on the Low Side MOSFET. When the
SMOD# pin is pulled LOW, the low-side MOSFET is
gated off. If the SMOD# pin is connected to the PWM
controller, the controller can actively enable or disable
SMOD# when the controller detects light-load condition
from output current sensing. Normally this pin is active
LOW. See Figure 28 for timing delays.
GS
LOW
HS turn -on with SMOD# LOW
CCM
V
IL_SMOD
V
IH_PWM
t
PD_PHGHH
10%
GH
0
0
0
1
0
1
Delay from SMOD# going
DCM
HIGH to LS V
t
PD_SHGLH
GL
0
0
0
0
1
0
www.fairchildsemi.com
V
GS
10%
IH_SMOD
GS
HIGH
V
OUT