IR3897MTRPBF International Rectifier, IR3897MTRPBF Datasheet - Page 25

• Manufacturer Part Number: IR3897MTRPBF
• Description: 4A Highly Integrated Single-Input Voltage, Synchronous Buck Regulator in a PQFN package.
• Manufacturer: International Rectifier

Specifications of IR3897MTRPBF

• Part Status: Active and Preferred
• Package: PQFN / 4 x 5
• Circuit: Single Output
• Iout (a): 4
• Switch Freq (khz): 0 - 1500
• Input Range (v): 1.0 - 16
• Output Range (v): 0.5 - 12
• Pbf: PbF Option Available

Any design or application using IR3897 must ensure
operation with a pulse width that is higher than this
minimum on‐time and preferably higher than 60 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 IR3897, the following condition
must be satisfied:
The minimum output voltage is limited by the reference
voltage and hence V
V
Therefore, at the maximum recommended input voltage
21V and minimum output voltage, the converter should be
designed at a switching frequency that does not exceed
396 kHz. Conversely, for operation at the maximum
recommended operating frequency (1.65 MHz) and
minimum output voltage (0.5V). The input voltage (PVin)
should not exceed 5.05V, otherwise pulse skipping will
happen.
out(min)
= 0.5 V,

t
on

25


V
t

on
in
V
V
t
on
(min)

in
in
F
D
(min)

s
F

FEBRUARY 02, 2012 |DATA SHEET | Rev 3.2
out(min)
s
F
F


s
s


t

on

V
V
= 0.5 V. Therefore, for
V
t

in
t
out
0.5
60
V
on
on
in
V

V
out
(min)
(min)
(min)
out

out
ns
F
V
s
F



s

. 8
Single‐Input Voltage, Synchronous Buck Regulator
33
(5)
(6)
(4)
V/uS
(3)
- 25 -
4A Highly Integrated SupIRBuck
MAXIMUM DUTY RATIO
A certain off‐time is specified for IR3897. This provides
an upper limit on the operating duty ratio at any given
switching frequency. The off‐time remains at a relatively
fixed ratio to switching period in low and mid frequency
range, while in high frequency range this ratio increases,
thus the lower the maximum duty ratio at which IR3897
can operate. Figure 21 shows a plot of the maximum duty
ratio vs. the switching frequency with built in input voltage
feed forward mechanism.
Figure 21: Maximum duty cycle vs. switching frequency.
TM
IR3897
PD‐97663