Datasheet LTC7862 (Analog Devices) - 9

link to page 15 link to page 21 LTC7862
PIN FUNCTIONS (QFN/TSSOP) SS (Pin 1/Pin 3):
Soft-Start Input. The LTC7862 attempts
BOOST (Pin 9/Pin 11):
Bootstrapped Supply to the to regulate the VFB voltage to the smaller of 0.8V or the Topside Floating Driver. A capacitor is connected between voltage on the SS pin. An internal 10μA pull-up current the BOOST and SW pins and an external low leakage diode source is connected to this pin. A capacitor to ground at is tied between the BOOST and DRVCC pins. Voltage swing this pin sets the ramp time to final regulated output volt- at the BOOST pin is from approximately DRVCC to (VIN + age during startup or during a retry. DRVCC). When TG is statically on during normal opera-
V
tion, BOOST is approximately 9V above SW.
FB (Pin 2/Pin 4):
Feedback Input. This pin receives the remotely sensed feedback voltage from an external resis-
BG (Pin 10/Pin 12):
High Current Gate Drive for Bottom tor divider across the output. (Synchronous) N-Channel MOSFET. Voltage swing at this
ITH (Pin 3/Pin 5):
Error Amplifier Output and Switching pin is from ground to DRVCC. Regulator Compensation Point. The current comparator
GND (Pin 11, Exposed Pin 21/Pin 13, Exposed Pad Pin
trip point increases with this control voltage.
21):
Ground. All GND pins must be tied together for oper-
TMR (Pin 4/Pin 6):
Programmable Fault Timer Input. A ation. The exposed pad must be soldered to PCB ground timing capacitor C for rated electrical and thermal performance. TMR, connected between this pin and GND, sets the amount of time that can be spent switching
DRVCC (Pin 12/Pin 14):
Output of the VIN or EXTVCC (during an overvoltage, overcurrent, and/or startup condi- Low Dropout Regulators. The gate drivers are powered tion.) It also sets the cool-down time before the LTC7862 from this voltage source. The DRVCC voltage is set by the will retry. See Applications Information. DRVUV pin. Must be decoupled to ground with a mini-
FREQ (Pin 5/Pin 7):
Frequency Control Pin for the Internal mum of 4.7µF ceramic or other low ESR capacitor, as VCO. Connecting the pin to GND forces the VCO to a fixed close as possible to the IC. Do not use the DRVCC pin for low frequency of 350kHz. Connecting the pin to INTV any other purpose. CC forces the VCO to a fixed high frequency of 535kHz. Other
VIN (Pin 13/Pin 15):
Main Supply Pin. A bypass capacitor frequencies between 50kHz and 900kHz can be pro- should be tied between this pin and GND. grammed by using a resistor between FREQ and GND.
EXTV
An internal 20µA pull-up current develops the voltage to
CC (Pin 14/Pin 16):
External Power Input to an Internal LDO linear regulator Connected to DRV be used by the VCO to control the frequency. CC. This LDO supplies DRVCC power from EXTVCC, bypassing
WARNB (Pin 6/Pin 8):
Open-Drain Logic Output. This the internal LDO powered from VIN whenever EXTVCC pin pulls low to GND whenever the LTC7862 is switch- is higher than its switchover threshold (4.7V or 7.7V ing (during an overvoltage, overcurrent, and/or startup depending on the DRVUV pin). See DRVCC Regulators in condition.) The typical pull-down impedance is 10Ω. The the Applications Information section. Do not exceed 14V WARNB pin enters a high-impedance state 60µs after on this pin. Do not connect EXTVCC to a voltage greater LTC7862 enters dropout with the top external MOSFET than VIN. on continuously. The WARNB pin is also pulled low during
RUN (Pin 15/Pin 17):
Run Control Input. Forcing this pin shutdown and during the cool-down period before a retry. below 1.12V shuts down the controller. Forcing this pin
TG (Pin 7/Pin 9):
High Current Gate Drive for Top below 0.7V shuts down the entire LTC7862, reducing qui- N-Channel MOSFET. This is the output of the floating high escent current to approximately 10µA. This pin can be side driver with a voltage swing from SW to BOOST. tied to VIN for always-on operation. Do not float this pin.
SW (Pin 8/Pin 10):
Switch Node Connection to Inductor. Rev 0 For more information www.analog.com 9 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS TIMING DIAGRAM FUNCTIONAL DIAGRAM OPERATION APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION TYPICAL APPLICATION RELATED PARTS