IR3841WMPBF International Rectifier, IR3841WMPBF Datasheet - Page 17

• Manufacturer Part Number: IR3841WMPBF
• Description: HIGHLY EFFICIENT INTEGRATED 8A SYNCHRONOUS BUCK REGULATOR
• Manufacturer: International Rectifier

Minimum on time Considerations
The minimum ON time is the shortest amount of
time for which the Control FET may be reliably
turned on, and this depends on the internal
timing delays. For the IR3841W, the typical
minimum on-time is specified as 50 ns.
Any design or application using the IR3841W
must ensure operation with a pulse width that is
higher than this minimum on-time and preferably
higher than 100 ns. This is necessary for the
circuit to operate without jitter and pulse-
skipping, which can cause high inductor current
ripple and high output voltage ripple.
In any application that uses the IR3841W, the
following condition must be satisfied:
The minimum output voltage is limited by the
reference voltage and hence V
Therefore, for V
Therefore, at the maximum recommended input
voltage 16V and minimum output voltage, the
converter should be designed at a switching
frequency that does not exceed 440 kHz.
Conversely, for operation at the maximum
recommended operating frequency 1.65 MHz
and minimum output voltage, any voltage above
4.2 V may not be stepped down without pulse-
skipping.
Rev 5.0
∴
∴
V
∴
∴
in
t
V
on
V
t
×
in
on
t
(min)
in
on
F
×
(min)
×
s
out(min)
F
=
=
F
s
≤
≤
V
s
F
D
≤
≤
in
V
t
s
V
≤
on
t
V
out
100
out
×
on
0.7
= 0.7 V,
t
in
V
on
V
(min)
(min)
F
out
×
out
(min)
s
ns
V
F
s
=
7 ×
out(min)
10
6
V/s
= 0.7 V.
Maximum Duty Ratio Considerations
A fixed off-time of 200 ns maximum is specified
for the IR3841W. This provides an upper limit on
the operating duty ratio at any given switching
frequency. It is clear, that higher the switching
frequency, the lower is the maximum duty ratio at
which the IR3841W can operate. To allow a
margin of 50ns, the maximum operating duty
ratio in any application using the IR3841W
should still accommodate about 250 ns off-time.
Fig 10. shows a plot of the maximum duty ratio
v/s the switching frequency, with 250 ns off-time.
Fig. 10. Maximum duty cycle v/s switching
95
90
85
80
75
70
65
60
55
250
frequency.
450
650
S w itching Frequency (kH z )
IR3841WMPbF
M a x Duty Cycle
850
1050
1250
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