iru3037acftr International Rectifier Corp., iru3037acftr Datasheet - Page 4

• Manufacturer Part Number: iru3037acftr
• Description: 8 Pwm 200 Khz Sync Contr In A 8-pin Tssop Package
• Manufacturer: International Rectifier Corp.

IRU3037/IRU3037A & (PbF)
BLOCK DIAGRAM
THEORY OF OPERATION
Introduction
The IRU3037 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 200 KHz (400 KHz
for “A” version).
Soft-Start
The IRU3037 has a programmable soft-start to control
the output voltage rise and limit the current surge at the
start-up. To ensure correct start-up, the soft-start se-
quence initiates when the Vc and Vcc rise above their
threshold (3.3V and 4.2V respectively) and generates
4
SS/SD
Comp 7
POR
Fb 1
1.25V
8
3V
20uA
25K
25K
64uA Max
Figure 2 - Simplified block diagram of the IRU3037.
Error Amp
3.5V
4.0V
Vcc
Vc
0.5V
Ct
www.irf.com
Oscillator
FbLo Comp
Error Comp
0.2V
0.2V
the Power On Reset (POR) signal. Soft-start function
operates by sourcing an internal current to charge an
external capacitor to about 3V. Initially, the soft-start func-
tion clamps the E/A’s output of the PWM converter. As
the charging voltage of the external capacitor ramps up,
the PWM signals increase from zero to the point the
feedback loop takes control.
Short-Circuit Protection
The outputs are protected against the short-circuit. The
IRU3037 protects the circuit for shorted output by sens-
ing the output voltage (through the external resistor di-
vider). The IRU3037 shuts down the PWM signals, when
the output voltage drops below 0.6V (0.4V for IRU3037A).
The IRU3037 also protects the output from over-voltaging
when the control FET is shorted. This is done by turning
on the sync FET with the maximum duty cycle.
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.
POR
Generator
Bias
Reset Dom
S
R
Q
3V
1.25V
POR
6
5
2
3
4
LDrv
Vc
HDrv
Vcc
Gnd