Datasheet LT1950 (Analog Devices) - 7
| Fabricante | Analog Devices |
| Descripción | Single Switch PWM Controller with Auxiliary Boost Converter |
| Páginas / Página | 20 / 7 — PI FU CTIO S. BLANK (Pin 9):. BOOST (Pin 14):. SENSE (Pin 10):. VIN (Pin … |
| Formato / tamaño de archivo | PDF / 223 Kb |
| Idioma del documento | Inglés |
PI FU CTIO S. BLANK (Pin 9):. BOOST (Pin 14):. SENSE (Pin 10):. VIN (Pin 15):. IN2 (Pin 11):. GATE (PIN 12):. VSEC (Pin 16):
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LT1950
U U U PI FU CTIO S BLANK (Pin 9):
The BLANK pin is used to adjust the
BOOST (Pin 14):
The BOOST pin is the NPN collector leading edge blanking period of the current sense amplifier output of the internal boost converter which can be used during FET turn-on. Shorting the BLANK pin to ground to generate an 11V supply for the MOSFET gate driver provides a default blanking period of approximately 110ns. circuit. The boost converter runs with a fixed off-time of A resistor from the BLANK pin to ground increases the 0.5µs and a current limit of 125mA. The converter runs blanking period up to 290ns for RBLANK = 75k. until the VIN2 voltage exceeds 11V and then turns off until
I
the VIN2 voltage drops below 10V. If the VIN2 voltage is
SENSE (Pin 10):
The ISENSE pin is the current sense input for the control loop. Connect this pin to the sense resistor supplied externally, the BOOST pin should be shorted to in the source of the external power MOSFET. ground or left open.
V VIN (Pin 15):
The VIN pin is the main supply pin for the
IN2 (Pin 11):
The VIN2 pin is the supply pin for the MOSFET gate drive circuit. Power can be supplied to this LT1950. This pin must be closely bypassed to ground. If pin by an external supply such as V VIN2 is generated using the BOOST pin then the LT1950 IN, and must exceed 8V (the undervoltage lockout threshold for the gate driver will be fully functional, internal VREF will be active and the supply). For low V gate output will be enabled with a VIN voltage as low as 3V. IN supply voltages an internal boost regulator can be used to generate as much as 11V at the An internal undervoltage lockout threshold exists at ap- V proximately 2.6V on the VIN pin. Undervoltage lockout IN2 pin. This allows the LT1950 to run with VIN supply voltages down to 3V while still supplying enough gate voltages greater than 3V can be programmed using a drive for standard level MOSFETs. voltage divider on the SHDN pin.
GATE (PIN 12):
The GATE pin is the output of a high current
VSEC (Pin 16):
The VSEC pin is used to program the gate drive circuit used to drive an external MOSFET. The maximum duty cycle of the gate driver circuit. The maxi- output is actively clamped to a max voltage of 13V if V mum duty cycle will be equal to (105/VSEC)% for VSEC IN2 is supplied by a high voltage. between 1.4V and 2.8V. This is a useful function to limit the flyback voltage in a forward converter. If the maximum
PGND (Pin 13):
This is the ground connection for the high duty cycle function is not used then the VSEC pin should be current gate driver stage. See the Applications Informa- tied to ground. tion section for recommendations on ground connec- tions. 1950fa 7
U U U PI FU CTIO S BLANK (Pin 9):
The BLANK pin is used to adjust the
BOOST (Pin 14):
The BOOST pin is the NPN collector leading edge blanking period of the current sense amplifier output of the internal boost converter which can be used during FET turn-on. Shorting the BLANK pin to ground to generate an 11V supply for the MOSFET gate driver provides a default blanking period of approximately 110ns. circuit. The boost converter runs with a fixed off-time of A resistor from the BLANK pin to ground increases the 0.5µs and a current limit of 125mA. The converter runs blanking period up to 290ns for RBLANK = 75k. until the VIN2 voltage exceeds 11V and then turns off until
I
the VIN2 voltage drops below 10V. If the VIN2 voltage is
SENSE (Pin 10):
The ISENSE pin is the current sense input for the control loop. Connect this pin to the sense resistor supplied externally, the BOOST pin should be shorted to in the source of the external power MOSFET. ground or left open.
V VIN (Pin 15):
The VIN pin is the main supply pin for the
IN2 (Pin 11):
The VIN2 pin is the supply pin for the MOSFET gate drive circuit. Power can be supplied to this LT1950. This pin must be closely bypassed to ground. If pin by an external supply such as V VIN2 is generated using the BOOST pin then the LT1950 IN, and must exceed 8V (the undervoltage lockout threshold for the gate driver will be fully functional, internal VREF will be active and the supply). For low V gate output will be enabled with a VIN voltage as low as 3V. IN supply voltages an internal boost regulator can be used to generate as much as 11V at the An internal undervoltage lockout threshold exists at ap- V proximately 2.6V on the VIN pin. Undervoltage lockout IN2 pin. This allows the LT1950 to run with VIN supply voltages down to 3V while still supplying enough gate voltages greater than 3V can be programmed using a drive for standard level MOSFETs. voltage divider on the SHDN pin.
GATE (PIN 12):
The GATE pin is the output of a high current
VSEC (Pin 16):
The VSEC pin is used to program the gate drive circuit used to drive an external MOSFET. The maximum duty cycle of the gate driver circuit. The maxi- output is actively clamped to a max voltage of 13V if V mum duty cycle will be equal to (105/VSEC)% for VSEC IN2 is supplied by a high voltage. between 1.4V and 2.8V. This is a useful function to limit the flyback voltage in a forward converter. If the maximum
PGND (Pin 13):
This is the ground connection for the high duty cycle function is not used then the VSEC pin should be current gate driver stage. See the Applications Informa- tied to ground. tion section for recommendations on ground connec- tions. 1950fa 7