IR3651STRPBF International Rectifier, IR3651STRPBF Datasheet - Page 10
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IR3651STRPBF
Manufacturer Part Number
IR3651STRPBF
Description
IC CTLR PWM SYNC DC-DC 14SOIC
Manufacturer
International Rectifier
Datasheet
1.IR3651SPBF.pdf
(19 pages)
Specifications of IR3651STRPBF
Pwm Type
Voltage Mode
Number Of Outputs
1
Frequency - Max
460kHz
Duty Cycle
80%
Voltage - Supply
4.5 V ~ 13.2 V
Buck
Yes
Boost
No
Flyback
No
Inverting
No
Doubler
No
Divider
No
Cuk
No
Isolated
No
Operating Temperature
0°C ~ 125°C
Package / Case
14-SOIC (3.9mm Width), 14-SOL
Frequency-max
460kHz
Package
14-Pin SOIC (NB)
Circuit
Sync PWM Controller
Vcc (min)
4.5
Vcc (max)
13.2
Iout (a)
25
Switch Freq (khz)
programmable to 400kHz
Pbf
PbF Option Available
For Use With
IRDC3651 - KIT REF DESIGN SYNCH BUCK REG
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
IR3651STRPBF
Manufacturer:
IR
Quantity:
20 000
For a given start-up time, the soft-start capacitor
(nF) can be estimated as:
Soft-Start
The IR3651 has programmable soft-start to
control the output voltage rise and limit the inrush
current during start-up.
To
sequence initiates when Vcc rises above its
threshold and generate the Power On Ready
(POR) signal. The soft-start function operates by
sourcing current to charge an external capacitor
to about 3V.
Initially, the soft-start function clamps the output
of error amplifier by injecting a current (64uA)
into the Fb pin and generates a voltage about
1.6V (64ux25K) across the negative input of error
amplifier (see figure 4).
The magnitude of the injected current is inversely
proportional to the voltage at the soft-start pin. As
the soft-start voltage ramps up, the injected
current decreases linearly and so does the
voltage at negative input of error amplifier.
When the soft-start capacitor is around 1V, the
voltage at the positive input of the error amplifier
is approximately 1.25V.
The output of error amplifier will start increasing
and generating the first PWM signal. As the soft-
start capacitor voltage continues to go up, the
current flowing into the Fb pin will keep
decreasing.
The feedback voltage increases linearly as the
soft start voltage ramps up. When soft-start
voltage is around 2V the output voltage is
reached the steady state and the injected current
is zero.
Figure 5 shows the theoretical operational
waveforms during soft-start.
The output voltage start-up time is the time
period
increases from 1V to 2V.
The start-up time will be dependent on the size of
the external soft-start capacitor and can be
estimate by:
12/07/2010
ensure
C
when
SS
20
≅
20
μA
correct
μ
∗
A
soft-start
T
C
*
start
ss
T
start
=
(
2
start-up,
ms
V
−
)
1
V
capacitor
--(
) 1
the
soft-start
voltage
Voltage at negative input
SS/SD
Comp
Voltage at Fb pin
1.25V
Output of UVLO
Current flowing
Fig. 5: Theoretical operation waveforms
Fig. 4: Soft-Start circuit for IR3651
Fb
of Error Amp
POR
into Fb pin
Soft-Start
20uA
Voltage
POR
during soft-start
25K
25K
64uA
≅ 1.6V
0V
0V
IR3651SPBF
3V
64uA
Error Amp
1.25V
1.25V
0uA
≅ 1V
≅ 2V
3V
10