FDMF6706B Fairchild Semiconductor, FDMF6706B Datasheet - Page 14

• Manufacturer Part Number: FDMF6706B
• Manufacturer: Fairchild Semiconductor

© 2011 Fairchild Semiconductor Corporation
FDMF6706B • Rev. 1.0.1
Skip Mode (SMOD)
The SMOD function allows higher converter efficiency
under light-load conditions. During SMOD, the low-side
FET gate signal is disabled (held LOW), preventing
discharging of the output capacitors as the filter inductor
current attempts reverse current flow – also known as
Diode Emulation Mode.
When the SMOD# pin is pulled HIGH, the synchronous
buck converter will work in Synchronous Mode. This
mode allows for gating on the low-side FET. When the
SMOD# pin is pulled LOW, the low-side FET 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. This pin is active LOW.
See Figure 26 for timing delays.
SMOD#
PWM
GH
VSWH
to
VSWH
GL
V
IH_PWM
t
PD_PHGLL
t
D_DEADON
1.0V
90%
t
PD_PLGHL
t
V
D_DEADOFF
90%
10%
IL_PWM
2.2V
10%
CCM
Figure 26.
Delay from SMOD# going
SMOD Timing Diagram
LOW to LS V
14
t
PD_SLGLL
Table 2.
Note:
4.
GS
DISB#
LOW
0
1
1
1
1
1
The SMOD feature is intended to have low
propagation delay between the SMOD signal and
the low-side FET V
diode emulation on a cycle-by-cycle basis.
HS turn -on with SMOD# LOW
CCM
V
IL_SMOD
V
IH_PWM
t
PD_PHGHH
SMOD Logic
3-State
PWM
X
0
1
0
1
10%
SMOD#
GS
X
X
0
0
1
1
response time to control
Delay from SMOD# going
DCM
GH
0
0
0
1
0
1
HIGH to LS V
t
PD_SHGLH
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V
GS
10%
IH_SMOD
HIGH
V
GL
OUT
0
0
0
0
1
0