参数资料
型号: IR3624MTRPBF
厂商: International Rectifier
英文描述: HIGH FREQUENCY SYNCHRONOUS PWM BUCK CONTROLLER
中文描述: 高频同步PWM降压控制器
文件页数: 8/21页
文件大小: 803K
代理商: IR3624MTRPBF
IR3624MPBF
Circuit Description
8
THEORY OF OPEARTION
Introduction
The
IR3624
synchronous controller and operates with a fixed
600kHz switching frequency, allowing the use of
small external components. The output voltage is
set by feedback pin (Fb) and the internal
reference voltage (0.6V). These are two inputs to
error amplifier. The error signal between these
two inputs is compared to a fixed frequency
linear sawtooth ramp and generates fixed
frequency pulses of variable duty-cycle (D) which
drivers N-channel external MOSFETs.
The timing of the IC is controlled by an internal
oscillator circuit that uses on-chip capacitor to set
the switching frequency.
The IR3624 operates with single input voltage
from 4.5V to 12V allowing an extended operating
input voltage range.
The current limit is programmable and uses on-
resistance of the low-side MOSFET, eliminating
the need for external current sense resistor
.
is
a
voltage
mode
PWM
Under-Voltage Lockout
The under-voltage lockout circuit monitors the
two input supplies (Vcc and Vc) and assures that
the MOSFET driver outputs remain in the off
state whenever the supply voltage drops below
set thresholds. Lockout occurs if Vc or Vcc fall
below 3.3V and 4.2V respectively. Normal
operation resumes once Vc and Vcc rise above
the set values.
Thermal Shutdown
Temperature sensing is provided inside IR3624.
The trip threshold is typically set to 145
o
C. When
trip threshold is exceeded, thermal shutdown
turns off both MOSFETs. Thermal shutdown is
not latched and automatic restart is initiated
when the sensed temperature drops within the
operating range. There is a 20
o
C hysteresis in
the thermal shutdown threshold.
Shutdown
The output can be shutdown by pulling the soft-
start pin below 0.3V. This can be easily done by
using an external small signal transistor. During
shutdown both MOSFET drivers will be turned
off. Normal operation will resume by cycling soft
start pin.
Error Amplifier
The IR3624 is a voltage mode controller. The
error amplifier is of transconductance type. The
amplifier is capable of operating with Type III
compensation control scheme using low ESR
output capacitance.
Pre-Bias Startup
IR3624 is able to start up into pre-charged
output,
which
prevents
disturbances of the output voltage.
The output starts in asynchronous fashion and
keeps the synchronous MOSFET off until the first
gate signal for control MOSFET is generated.
Figure 4 shows a typical Pre-Bias condition at
start up.
Depends on system configuration, specific
amount of output capacitors may be required to
prevent discharging the output voltage.
oscillation
and
Fig. 4: Pre-Bias start up
Vo
Time
Volt
Pre-Bias Voltage
(Output Voltage before startup)
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