Datasheet LTC3871, LTC3871-1 (Analog Devices) - 8

LTC3871/LTC3871-1
TYPICAL PERFORMANCE CHARACTERISTICS Maximum Current Sense Threshold Maximum Current Sense Threshold vs Feedback Voltage (DCR) vs Feedback Voltage (RSENSE) (LTC3871-1) (LTC3871-1)
60 70 60 50 V5 V5 50 40 3/4 V5 3/4 V5 40 30 FLOAT FLOAT 30 20 1/4 V5 1/4 V5 20 10 GND 10 GND MAXIMUM CURRENT SENSE THRESHOLD (mV) 0 MAXIMUM CURRENT SENSE THRESHOLD (mV) 0 0 0.2 0.4 0.6 0.8 1.0 1.2 0 0.2 0.4 0.6 0.8 1.0 1.2 FEEDBACK VOLTAGE (V) FEEDBACK VOLTAGE (V) 3871 G19 3871 G20
PIN FUNCTIONS SS (Pin 1):
Soft-Start Input. The voltage ramp rate at this
UVHIGH (Pin 9):
VHIGH Undervoltage Threshold Set Pin. A pin sets the voltage ramp rate of the regulated voltage. resistor divider from VHIGH is needed to set this threshold. A capacitor to ground accomplishes soft-start in buck This pin also controls the state of the PGATE pin. When mode. This pin has a 1.25µA pull-up current. the voltage on this pin falls below the 1.2V trip point,
VFB
a 5µA current is sunk into the pin to provide externally
LOW (Pin 2):
VLOW Voltage Sensing Error Amplifier Inverting Input. adjustable hysteresis.
ITH OV LOW/ITHHIGH (Pins 3 and 4):
Current Control Threshold
LOW (Pin 10):
VLOW Overvoltage Threshold Set Pin. A and Error Amplifier Compensation Point. The current com- resistor divider from VLOW is needed to set this thresh- parator’s threshold varies with the ITH control voltage. old. When the voltage on this pin rises past the 1.2V trip point, a 5µA current is sourced out of the pin to provide
VFBHIGH (Pin 5):
VHIGH Voltage Sensing Error Amplifier externally adjustable hysteresis. Inverting Input.
IMON (Pin 11):
The voltage on this pin is directly propor-
V5 (Pin 6):
Internal 5.5V Regulator Output. The control tional to the average inductor currents of the 2 channels. circuits are powered from this voltage. Bypass this pin 1.25V indicates zero average inductor current per phase. to SGND with a minimum of 4.7µF low ESR tantalum or ceramic capacitor.
SETCUR (Pin 12):
This pin sets the maximum average inductor current in buck or boost mode. This pin sources
SGND (Pins 7 and 28):
Signal Ground Pins. 7.5µA.
OVHIGH (Pin 8):
VHIGH Overvoltage Threshold Set Pin. A
SNSA1+/SNSA2+ (Pins 13 and 48):
AC Positive Current resistor divider from VHIGH is needed to set this thresh- Sense Comparator Inputs. These inputs amplify the AC old. When the voltage on this pin rises past the 1.2V trip portion of the current signal to the IC’s current comparator. point, a 5µA current is sourced out of the pin to provide externally adjustable hysteresis. When OVHIGH voltage is
SNS1–/SNS2–(Pins 14 and 47):
Negative Current Sense above 3V, the controller stops switching. Comparator Inputs. The negative input of the current comparator is normally connected to VLOW. Rev. B 8 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 Typical Application Related Parts