LT1950 データシートの表示（PDF） - Linear Technology

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LT1950

Single Switch PWM Controller with Auxiliary Boost Converter

Linear Technology 

LT1950

PI FU CTIO S

BLANK (Pin 9): The BLANK pin is used to adjust the

leading edge blanking period of the current sense amplifier

during FET turn-on. Shorting the BLANK pin to ground

provides a default blanking period of approximately 110ns.

A resistor from the BLANK pin to ground increases the

blanking period up to 290ns for RBLANK = 75k.

ISENSE (Pin 10): The ISENSE pin is the current sense input

for the control loop. Connect this pin to the sense resistor

in the source of the external power MOSFET.

VIN2 (Pin 11): The VIN2 pin is the supply pin for the

MOSFET gate drive circuit. Power can be supplied to this

pin by an external supply such as VIN, and must exceed 8V

(the undervoltage lockout threshold for the gate driver

supply). For low VIN supply voltages an internal boost

regulator can be used to generate as much as 11V at the

VIN2 pin. This allows the LT1950 to run with VIN supply

voltages down to 3V while still supplying enough gate

drive for standard level MOSFETs.

GATE (PIN 12): The GATE pin is the output of a high current

gate drive circuit used to drive an external MOSFET. The

output is actively clamped to a max voltage of 13V if VIN2

is supplied by a high voltage.

PGND (Pin 13): This is the ground connection for the high

current gate driver stage. See the Applications Informa-

tion section for recommendations on ground connec-

tions.

BOOST (Pin 14): The BOOST pin is the NPN collector

output of the internal boost converter which can be used

to generate an 11V supply for the MOSFET gate driver

circuit. The boost converter runs with a fixed off-time of

0.5µs and a current limit of 125mA. The converter runs

until the VIN2 voltage exceeds 11V and then turns off until

the VIN2 voltage drops below 10V. If the VIN2 voltage is

supplied externally, the BOOST pin should be shorted to

ground or left open.

VIN (Pin 15): The VIN pin is the main supply pin for the

LT1950. This pin must be closely bypassed to ground. If

VIN2 is generated using the BOOST pin then the LT1950

will be fully functional, internal VREF will be active and the

gate output will be enabled with a VIN voltage as low as 3V.

An internal undervoltage lockout threshold exists at ap-

proximately 2.6V on the VIN pin. Undervoltage lockout

voltages greater than 3V can be programmed using a

voltage divider on the SHDN pin.

VSEC (Pin 16): The VSEC pin is used to program the

maximum duty cycle of the gate driver circuit. The maxi-

mum duty cycle will be equal to (105/VSEC)% for VSEC

between 1.4V and 2.8V. This is a useful function to limit the

flyback voltage in a forward converter. If the maximum

duty cycle function is not used then the VSEC pin should be

tied to ground.

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