Datasheet LTC7800 (Analog Devices) - 8

LTC7800
TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency vs Input Undervoltage Lockout Threshold Voltage vs Temperature Shutdown Current vs Temperature
945 4.2 22 FREQ = GND VIN = 12V 944 4.1 20 943 18 942 4.0 RISING 941 16 3.9 939 VOLTAGE (V) CC 14 FALLING 938 3.8 INTV 12 937 SHUTDOWN CURRENT (µA) OSCILLATOR FREQUENCY (kHz) 3.7 936 10 935 3.6 8 5 15 25 35 45 55 65 –75 –50 –25 0 25 50 75 100 125 150 –75 –50 –25 0 25 50 75 100 125 150 INPUT VOLTAGE (V) TEMPERATURE (°C) TEMPERATURE (°C) 7800 G25 7800 G26 7800 G27
PIN FUNCTIONS PLLIN/MODE (Pin 1):
External Synchronization Input to
RUN (Pin 4):
Digital Run Control Input. Forcing this pin Phase Detector and Forced Continuous Mode Input. When below 1.16V shuts down the controller. Forcing this pin an external clock is applied to this pin, the phase-locked below 0.7V shuts down the entire LTC7800, reducing loop will force the rising TG signal to be synchronized with quiescent current to approximately 14µA. the rising edge of the external clock, and the regulator
SENSE– (Pin 5):
The (–) Input to the Differential Current operates in forced continuous mode. When not synchro- Comparator. When greater than INTV nizing to an external clock, this input determines how the CC – 0.5V, the SENSE– pin supplies power to the current comparator. LTC7800 operates at light loads. Pulling this pin to ground selects Burst Mode operation. An internal 100k resistor to
SENSE+ (Pin 6):
The (+) input to the differential current ground also invokes Burst Mode operation when the pin is comparator is normally connected to DCR sensing net- floated. Tying this pin to INTVCC forces continuous inductor work or current sensing resistor. The ITH pin voltage and current operation. Tying this pin to a voltage greater than controlled offsets between the SENSE– and SENSE+ pins 1.2V and less than INTVCC –1.3V selects pulse-skipping in conjunction with RSENSE set the current trip threshold. operation. This can be done by connecting a 100k resistor
V
from this pin to INTV
FB (Pin 7):
Receives the remotely sensed feedback volt- CC. age from an external resistive divider across the output.
SGND (Pins 2, 3, Exposed Pad Pin 21):
Small-signal
ITH (Pin 8):
Error Amplifier Outputs and Switching Regula- ground, must be routed separately from high current tor Compensation Point. The current comparator trip point grounds to the common (–) terminals of the CIN capacitor. increases with this control voltage. Pins 2, 3, Exposed Pad Pin 21, must both be electrically connected to small signal ground for proper operation. The exposed pad must be soldered to PCB ground for rated thermal performance. 7800f 8 For more information www.linear.com/LTC7800 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions FUNCTIONAL Diagram Operation Applications Information Typical Application Related Parts