IRDC3831 International Rectifier, IRDC3831 Datasheet - Page 15

• Manufacturer Part Number: IRDC3831
• Description: BOARD EVAL SYNC BUCK CONVERTER
• 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 IR3831, the typical
minimum on-time is specified as 50 ns.
Any design or application using the IR3831 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 IR3831, the
following condition must be satisfied:
The minimum output voltage for the IR3831 is
limited to V
Furthermore, for the IR3831, especially for active
bus termination applications, it is strongly
recommended to use a switching frequency of
400 kHz to obtain clean and jitter free operation
in sourcing as well as sinking modes. Therefore,
the maximum input voltage that may be stepped
down to 0.6V at 400 kHz without jitter or pulse
skipping is 15 V.
11/05/10
∴
∴
V
∴
∴
in
t
V
out(min)
on
V
t
in
×
on
t
(min)
in
on
F
×
(min)
×
s
F
=
=
F
s
= 0.6 V.
≤
≤
V
s
F
≤
D
≤
in
V
t
s
V
≤
on
t
V
out
100
on
out
×
0.6
t
in
V
on
(min)
V
(min)
F
out
×
out
(min)
s
ns
V
F
s
=
6
×
10
6
V/s
Maximum Duty Ratio Considerations
A fixed off-time of 200 ns maximum is specified
for the IR3831. 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 IR3831 can operate. To allow some
margin, the maximum operating duty ratio in any
application
accommodate about 250 ns off-time. Fig 9.
shows a plot of the maximum duty ratio v/s the
switching frequency, with 250 ns off-time.
Fig. 9. Maximum duty cycle v/s switching
95
90
85
80
75
70
65
60
55
250
frequency.
450
using
650
S w itching Frequency (kH z )
M a x Duty Cycle
the
850
IR3831MPbF
IR3831
1050
1250
should
1450
15
still
1650