IR3637ASPBF International Rectifier, IR3637ASPBF Datasheet - Page 4

• Manufacturer Part Number: IR3637ASPBF
• Description: IC CTLR SYNC BUCK REG 8-SOIC
• Manufacturer: International Rectifier

Specifications of IR3637ASPBF

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 660kHz
• Duty Cycle: 76%
• Voltage - Supply: 4.5 V ~ 5.5 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: 8-SOIC (3.9mm Width)
• Frequency-max: 660kHz
• Package: 8-Pin SOIC(NB)
• Circuit: Sync PWM Controller with 1% accuracy
• Vcc (min): 4.0
• Vcc (max): 25
• Vout (min): 0.8
• Vout (max): Vcc * 0.85
• Iout (a): 15
• Switch Freq (khz): Internal 600kHz
• Pbf: PbF Option Available
• For Use With: IRPP3637-12A - KIT REF DES 12A 1PH SYNC BUCKIRDC3637 - BOARD EVAL SYNC BUCK REGULATOR
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

IR3637ASPbF
BLOCK DIAGRAM
THEORY OF OPERATION
Introduction
The IR3637A is a fixed frequency, voltage mode syn-
chronous controller and consists of a precision refer-
ence voltage, an error amplifier, an internal oscillator, a
PWM comparator, 0.5A peak gate driver, soft-start and
shutdown circuits (see Block Diagram).
The output voltage of the synchronous converter is set
and controlled by the output of the error amplifier; this is
the amplified error signal from the sensed output voltage
and the reference voltage.
This voltage is compared to a fixed frequency linear
sawtooth ramp and generates fixed frequency pulses of
variable duty-cycle, which drives the two N-channel ex-
ternal MOSFETs.The timing of the IC is provided through
an internal oscillator circuit which uses on-chip capaci-
tor to set the oscillation frequency to 600 KHz.
4
SS/SD
Comp 7
POR
Fb 1
8
0.8V
3V
25uA
25K
25K
64uA Max
Figure 2 - Simplified block diagram of the IR3637A.
Error Amp
3.3V
4.2V
Vcc
Vc
0.4V
Ct
Oscillator
FbLo Comp
Error Comp
Short-Circuit Protection
The output is protected against the short-circuit. The
IR3637A protects the circuit for shorted output by sens-
ing the output voltage (through the external resistor di-
vider). The IR3637A shuts down the PWM signals, when
the output voltage drops below 0.4V.
Under-Voltage Lockout
The under-voltage lockout circuit assures that the
MOSFET driver outputs remain in the off state whenever
the supply voltage drops below set parameters. Lockout
occurs if Vc or Vcc fall below 3.3V and 4.2V respec-
tively. Normal operation resumes once Vc and Vcc rise
above the set values.
Shutdown
The converter can be shutdown by pulling the soft-start
pin below 0.4V. This can be easily done by using an
external small signal transistor. During shutdown both
drivers turn off.
POR
Generator
Bias
Reset Dom
S
R
Q
3V
POR
0.8V
www.irf.com
6
5
3
4
2
LDrv
Vcc
Vc
HDrv
Gnd