T
echcode
®
40V, 600mA, 2MHz/1MHz synchronous Buck Converter
DATASHEET
TD1465
Function Description
Main Control Loop
The TD1465 is a constant frequency, synchronous rectifier and
current-mode switching regulator. In normal peration, the internal
upper power MOSFET is turned on each cycle. The peak inductor
current at which ICMP turn off the upper MOSFET is controlled by
the voltage on the COMP node, which is the output of the error
amplifier (EAMP). An external resistive divider connected between
V
OUT
and ground allows the EAMP to receive an output feedback
voltage V
FB
at FB pin. When the load current increases, it causes a
slightly decrease in V
FB
relative to the 0.8V reference, which in turn
causes the COMP voltage to increase until the average inductor
current matches the new load current.
VIN Power-On-Reset (POR) and EN Under-voltage Lockout
The TD1465 keep monitoring the voltage on VIN pin to prevent
wrong logic operations which may occur when VIN voltage is not
high enough for the internal control circuitry to operate. The VIN
POR has a rising threshold of 3.9V (typical) with 0.6V of
hysteresis.
An external under-voltage lockout (UVLO) is sensed and
programmed at the EN pin. The EN UVLO has a rising threshold of
1.4V with 0.2V of hysteresis. The EN UVLO should be
programmed by connecting a resistive divider from VIN to EN to
GND.
After the VIN and EN voltages exceed their respective voltage
thresholds, the IC starts a start-up process and then ramps up the
output voltage to the setting of output voltage. Connect a RC
network from EN to GND to set a turn-on delay that can be used to
sequence the output voltages of multiple devices.
Soft-Start
The TD1465 provides built-in soft-start function to limit the inrush
current. The soft-start time is 1ms.
Bootstrap Capacitor
The TD1465 is a N-channel MOSFET step down converter. The
MOSFET requires a gate voltage that is higher than input voltage,
thus a boost capacitor should be connected between SW and BST
pins to drive the gate of the N-channel MOSFET. Typical boostrap
capacitor value is from 10nF to 100nF.
Over-Current-Protection and Hiccup
The TD1465 has a cycle-by-cycle over-current limit when the
inductor current peak value exceeds the set current limit threshold.
Meanwhile, the output voltage drops until FB is below the
Under-Voltage (UV) threshold below the reference. Once UV is
triggered, the TD1465 enters hiccup mode to periodically restart
the part.This protection mode is especially useful when the output
is dead-shorted to ground. The average short circuit current is
greatly reduced to alleviate thermal issues and to protect the
regulator. The TD1465 exits the hiccup mode once the
over-current condition is removed.
Over-Temperature Protection (OTP)
The over-temperature circuit limits the junction temperature of the
TD1465 When the junction temperature exceeds 150
o
C, a thermal
sensor turns off the N-channel power MOSFET, allowing the
device to cool down. The thermal sensor allows the converter to
start a start-up process and regulate the output voltage again after
the junction temperature cools by 30
o
C. The OTP designed with a
30
o
C hysteresis lowers the average T
J
during continuous thermal
overload conditions, increasing life time of the TD1465.
December, 15, 2012.
Techcode Semiconductor Limited
8
QQ:1929794238
TD [ 美国泰德半导体有限公司 ]
