Datasheet LT3791-1 (Analog Devices) - 9

LT3791-1
pin FuncTions CTRL (Pin 1):
Output Current Sense Threshold Adjustment
EN/UVLO (Pin 9):
Enable Control Pin. Forcing an accurate Pin. Regulating threshold V(ISP-ISN) is 1/10th of (VCTRL – 1.2V falling threshold with an externally programmable 200mV). CTRL linear range is from 200mV to 1.1V. For hysteresis is generated by the external resistor divider VCTRL > 1.3V, the current sense threshold is constant at and a 3µA pull-down current. Above the 1.2V (typical) the full-scale value of 100mV. For 1.1V < VCTRL < 1.3V, the threshold (but below 6V), EN/UVLO input bias current is dependence of the current sense threshold upon VCTRL tran- sub-µA. Below the falling threshold, a 3µA pull-down cur- sitions from a linear function to a constant value, reaching rent is enabled so the user can define the hysteresis with 98% of full scale by VCTRL = 1.2V. Connect CTRL to VREF the external resistor selection. An undervoltage condition for the 100mV default threshold. Force less than 175mV resets soft-start. Tie to 0.3V, or less, to disable the device (typical) to stop switching. Do not leave this pin open. and reduce VIN quiescent current below 1µA.
SS (Pin 2):
Soft-start reduces the input power sources
IVINP (Pin 10):
Positive Input for the Input Current Limit surge current by gradually increasing the controller’s cur- and Monitor. Input bias current for this pin is typically 90µA. rent limit. A minimum value of 22nF is recommended on
IVINN (Pin 11):
Negative Input for the Input Current Limit this pin. A 100k resistor must be placed between SS and and Monitor. The input bias current for this pin is typically VREF for the LT3791-1. 20µA.
PWM (Pin 3):
A signal low turns off switches, idles switch-
V
ing and disconnects the V
IN (Pin 12):
Main Input Supply. Bypass this pin to PGND C pin from all external loads. The with a capacitor. PWMOUT pin follows the PWM pin. PWM has an internal 90k pull-down resistor. If not used, connect to INTVCC.
INTVCC (Pin 13):
Internal 5V Regulator Output. The driver and control circuits are powered from this voltage. Bypass
C/10 (Pin 4):
C/10 Charge Termination Pin. An open-drain this pin to PGND with a minimum 4.7µF ceramic capacitor. pull-down on C/10 asserts if FB is greater than 1.15V (typi- cal) and V(ISP-ISN) is less than 10mV (typical). To function,
TG1 (Pin 14):
Top Gate Drive. Drives the top N-channel the pin requires an external pull-up resistor. MOSFET with a voltage equal to INTVCC superimposed on the switch node voltage SW1.
SHORT (Pin 5):
Output Shorted Pin. An open-drain pull- down on SHORT asserts if FB is less than 400mV (typical).
BST1 (Pin 15):
Bootstrapped Driver Supply. The BST1 pin To function, the pin requires an external pull-up resistor. swings from a diode voltage below INTVCC up to a diode voltage below V
V
IN + INTVCC.
REF (Pin 6):
Voltage Reference Output Pin, Typically 2V. This pin drives a resistor divider for the CTRL pin, either
SW1 (Pin 16):
Switch Node. SW1 pin swings from a diode for output current adjustment or for temperature limit/ voltage drop below ground up to VIN. compensation of the output load. Can supply up to 200µA
PGND (Pins 17, 20):
Power Ground. Connect these pins of current. closely to the source of the bottom N-channel MOSFET.
ISMON (Pin 7):
Monitor pin that produces a voltage that
BG1 (Pin 18):
Bottom Gate Drive. Drives the gate of the is ten times the voltage V(ISP-ISN). ISMON will equal 1V bottom N-channel MOSFET between ground and INTV when V CC. (ISP-ISN) = 100mV.
BG2 (Pin 19):
Bottom Gate Drive. Drives the gate of the
IVINMON (Pin 8):
Monitor pin that produces a voltage bottom N-channel MOSFET between ground and INTV that is twenty times the voltage V CC. (IVINP-IVINN). IVINMON will equal 1V when V
SW2 (Pin 21):
Switch Node. SW2 pin swings from a diode (IVINP-IVINN) = 50mV. voltage drop below ground up to VOUT. 37911fb For more information www.linear.com/LT3791-1 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Typical Application Related Parts