LTC7821 PIN FUNCTIONS TEMP (Pin 12): Temperature Sensing Input. Using a PTC TG2 (Pin 21): Floating Gate Drive for Second Lowermost resistor as the lower leg of a resistor divider, connect the N-Channel MOSFET. The voltage swings equal to INTVCC TEMP pin to the common point of the divider. The PTC superimposed on the switch node voltage SW3. resistor is used to monitor a hot spot on the PCB. Once BOOST1, BOOST2, BOOST3 (Pin 31, 23, 22): Bootstrapped it reaches the TEMP threshold of 1.22V, the LTC7821 Supplies to Floating Drivers. Capacitors are connected stops switching for 100ms before retrying. Ground this between the BOOSTx and SWx (MID) pin. Voltage swing pin if not used. at the BOOST1 pin is from (VIN/2 + INTVCC) to (VIN + IN- VFB (Pin 13): Error Amplifier Feedback Input. This pin TVCC). Voltage at the BOOST2 pin is at (VIN/2 + INTVCC). receives the remotely sensed feedback voltage from an Voltage swing at the BOOST3 pin is from INTVCC to (VIN/2 external resistive divider across the output. + INTVCC). ISNS– (Pin 14): Current Sense Comparator Input. The (–) BG1 (Pin 24): Floating Gate Drive for Second Uppermost input to the current comparator is Kelvin connected to the N-Channel MOSFET. The voltage swings between (VIN/2 output voltage of the controller. + INTVCC) and VIN/2. ISNS+ (Pin 15): Current Sense Comparator Input. The (+) MID (Pin 25): Half Supply from VIN. Do not use this to input to the current comparator is normally Kelvin con- source current. Connect a bypass capacitor from this nected to the DCR sensing networks or current sensing node to PGND. resistor. MIDSENSE (Pin 26): Half Supply Monitor. Provides Kelvin EXTVCC (Pin 16): External Power Input to an Internal LDO sensing input for the comparator that monitors the voltage Connected to INTVCC. This LDO supplies INTVCC power, between MIDSENSE and ground. An RC filter can be added bypassing the internal LDO powered from VIN whenever from MID to this pin to filter out noise. EXTVCC is higher than 6.4V. Do not float or exceed 40V V on this pin. IN_SENSE (Pin 27): VIN Kelvin Sensing Input. Allows an internal VIN/2 to be generated for LTC7821 control circuit PGND (Pin 17): Driver Power Ground. Connect this pin usage. For a cleaner supply, an RC filter can be added closely to the source of bottom (synchronous) N-channel from VIN to this pin. MOSFET M4, the (–) terminal of CIN and the (–) terminal V of C IN (Pin 28): Main Input Supply. Bypass this pin to PGND VCC. with a capacitor. BG2 (Pin 18): Gate Drive for the Bottom (synchronous) SW1 (Pin 29): Switch Node Connection to One Terminal N-Channel MOSFET. The voltage swings from slightly of Flying Capacitor. Voltage swing at this pin is from V below ground to INTV IN/2 CC. voltage to VIN. INTVCC (Pin 19): Internal Regulator Output. The bottom TG1 (Pin 30): Floating Gate Drive for Uppermost N-Channel synchronous gate driver and control circuits are powered MOSFET. The voltage swings equal to INTV from this regulator. Bypass this pin to PGND with a minimum CC superimposed on the switch node voltage SW1. of 4.7μF low ESR tantalum or ceramic capacitor. Do not use the INTVCC pin for any purpose other than described SGND (Exposed Pad, Pin 33): Signal Ground. All Small- in this data sheet. signal components and compensation components should connect to this ground, which in turn connects to PGND SW3 (Pin 20): Switch Node Connection to Inductor and at one point. Exposed pad must be soldered to the PCB, One Terminal of Flying Capacitor. Voltage swing at this pin providing a local ground for the control components of is from slightly below ground to VIN/2. the IC, and be tied to the PGND pin under the IC. Rev A 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Related Parts
