Datasheet LT3090 (Analog Devices) - 10

LT3090
pin FuncTions (DFN/MSOP) IN (Pins 1, 2, Exposed Pad 11/1, 2, 3, Exposed Pad
to a positive supply voltage (at least 2V above IMONP). If
13):
Input. These pins supply power to the regulator. The unused, tie IMONN to the GND pin. A parasitic substrate exposed backside pad of the DFN and MSOP packages is diode exists between the LT3090’s IMONN and IN pins. an electrical connection to IN and the device’s substrate. Therefore, do not drive IMONN more than 0.3V below IN For proper electrical and thermal performance, tie all IN during normal operation or during a fault condition. pins together and tie IN to the exposed backside of the
SHDN (Pin 6/7):
Shutdown. Use the SHDN pin to put the package on the PCB. See the Applications Information LT3090 into a micropower shutdown state and to turn off section for thermal considerations and calculating junc- the output voltage. The SHDN function is bidirectional, al- tion temperature. The LT3090 requires a bypass capaci- lowing either positive or negative logic to turn the regulator tor at IN. In general, a battery’s output impedance rises ON/OFF. The SHDN pin threshold voltages are referenced with frequency, so include a bypass capacitor in battery to GND. The output of the LT3090 is OFF if the SHDN pin is powered applications. An input bypass capacitor in the pulled within ±0.45V of GND. Driving the SHDN pin more range of 2.2µF to 4.7µF generally suffices, but applica- than ±1.4V turns the LT3090 ON. Drive the SHDN pin with tions with large load transients or longer input lines may either a logic gate or with open collector/drain logic using require higher input capacitance to prevent input supply a pull-up resistor. The resistor supplies the pull-up current droop or input ringing. of the open collector/drain gate. The maximum SHDN pin
ILIM (Pin 3/4):
Current Limit Programming Pin. Con- current is 7µA out of the pin (for negative logic) or 30µA necting an external resistor between the ILIM and IN pins into the pin (for positive logic). If the SHDN function is programs the current limit set point. For best accuracy, unused, connect the SHDN pin to VIN or a positive bias Kelvin connect this resistor to the IN pins. The program- voltage to turn the device ON. Do not float the SHDN pin. As ming scale factor is nominally 10A • kΩ. Current limit is detailed in the Applications Information section, the SHDN accurate to ±8% over temperature. If unused, tie ILIM to IN pin can also be used to set a programmable undervoltage and the internal current limit protects the part. A parasitic lockout (UVLO) threshold. A parasitic diode exists between substrate diode exists between the LT3090’s ILIM and IN the LT3090’s SHDN and IN pins. Therefore, do not drive pins. Therefore, do not drive ILIM more than 0.3V below SHDN more than 0.3V below IN during normal operation IN during normal operation or during a fault condition. or during a fault condition.
IMONP (Pin 4/5):
Positive Current Monitoring Pin. For
SET (Pin 7/8):
SET. This pin is the inverting input to the positive current monitoring, connect a resistor between error amplifier and the regulation setpoint for the device. IMONP and GND. IMONP sources current equal to 1/2000 A precision fixed current of 50µA flows into this pin. Con- of output current. For negative current monitoring, tie necting a resistor from SET to GND programs the LT3090’s this pin to IN. For proper operation, IN and IMONP must output voltage. Output voltage range is from zero to the be at least 2V below IMONN. If unused, tie IMONP to IN. –36V absolute maximum rating. Adding a bypass capacitor A parasitic substrate diode exists between the LT3090’s from SET to GND improves transient response, PSRR, noise IMONP and IN pins. Therefore, do not drive IMONP more performance and soft starts the output. Kelvin connect the than 0.3V below IN during normal operation or during a GND side of the SET pin resistor to the load for optimum fault condition. load regulation performance. A parasitic substrate diode exists between the LT3090’s SET and IN pins. Therefore,
IMONN (Pin 5/6):
Negative Current Monitoring Pin. For do not drive SET more than 0.3V below IN during normal negative current monitoring, connect a resistor between operation or during a fault condition. IMONN and GND. IMONN sinks current equal to 1/1000 of output current. For positive current monitoring, bias IMONN 3090fa 10 For more information www.linear.com/LT3090