Datasheet LT1950 (Analog Devices) - 6

LT1950
W U TYPICAL PERFOR A CE CHARACTERISTICS BOOST Switch Off Time vs Maximum Duty Cycle vs GATE Clamp Voltage vs Temperature VSEC Voltage Temperature
700 100 16 MAX DUTY CYCLE = (105/VSEC)% 90 1.25V < VSEC < 2.8V T 15 A = 25°C 600 80 14 70 500 13 60 12 50 400 MAXIMUM DUTY CYCLE (%) GATE CLAMP VOLTAGE (V) BOOST SWITCH OFF TIME (ns) 40 11 300 30 10 –50 –25 0 25 50 75 100 125 0.8 1.2 1.6 2.0 2.4 2.8 3.2 –50 –25 0 25 50 75 100 125 V TEMPERATURE ( SEC VOLTAGE (V) °C) TEMPERATURE (°C) 1950 G17 1950 G16 1950 G18
U U U PI FU CTIO S COMP (Pin 1):
The COMP pin is the output of the error
SLOPE (Pin 5):
The SLOPE pin is used to adjust the amplifier. The error amplifier is a true op amp which allows amount of slope compensation. Leaving the pin open the use of an RC network to be connected between the circuit results in a default level of slope compensation. The Comp and FB pins to compensate the feedback loop for amount of slope compensation can be adjusted above this optimum transient response. The peak switch current in default level by connecting a resistor from the SLOPE pin the external MOSFET will be proportional to the voltage on to the VREF pin. the COMP pin. Typical operating voltage range for this pin
V
is 1V to 2.5V.
REF (Pin 6):
The VREF pin is the output of an internal 2.5V reference. This pin is capable of sourcing up to 2.5mA for
FB (Pin 2):
The FB pin is the inverting input to the error external use. It is recommended that the VREF pin is amplifier. The output voltage is set with a resistor divider. bypassed to ground with a 0.1µF ceramic capacitor. The error amplifier adjusts the peak switch current to
SHDN (Pin 7):
The SHDN pin is used to put the device into maintain the FB pin voltage at the value of the internal a low power shutdown state. In shutdown the V reference voltage of 1.23V. IN supply current drops to 5µA. The SHDN pin has an accurate
ROSC (Pin 3):
A resistor from the ROSC pin to ground threshold of 1.32V which can be used to program an programs the operating frequency of the LT1950. Operat- undervoltage lockout threshold. Input current levels on ing frequency range is 100kHz to 500kHz. Nominal voltage the SHDN pin can be used to program hysteresis into the on the ROSC pin is 1V. undervoltage lockout levels.
SYNC (Pin 4):
The SYNC pin is used to synchronize the
GND (Pin 8):
The GND pin is the analog ground for the internal oscillator to an external clock signal. The pin is internal circuitry of the LT1950. Sensitive circuitry such as directly logic compatible and can be driven with any signal the feedback divider, frequency setting resistor, reference with a duty cycle of 10% to 90%. If the SYNC function is bypass capacitor should be tied directly to this pin. See the not used the pin can be left open circuit or connected to Applications Information section for recommendations ground. on ground connections. 1950fa 6