Datasheet LTC1704, LTC1704B (Analog Devices) - 7

LTC1704/LTC1704B
W U TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Temperature IPVCC, IBOOST vs Driver Load
6.0 35 VCC = PVCC = BOOST = 5V TA = 25°C TG, BG FLOAT PV 30 CC = BOOST = 5V IVCC 4.5 25 (mA) IPVCC 20 3.0 BOOST, I 15 IBOOST I PVCC SUPPLY CURRENT (mA) 10 1.5 5 0 0 –50 –25 0 25 50 75 100 125 0 2000 4000 6000 8000 10000 TEMPERATURE (°C) TG, BG LOAD (pF) 1704 G26 1704 G27
U U U PI FU CTIO S TG (Pin 1):
Switcher Controller Top Gate Drive. The TG pin
RUN/SS (Pin 4):
Switcher Controller Soft-Start. A capaci- drives the gate of the top N-channel MOSFET, QT. The TG tor from RUN/SS to GND controls the turn-on time and driver draws power from the BOOST pin and returns it to rate of rise of the switcher output voltage at power up. An the SW pin, providing true floating drive to QT. TG is de- internal 3µA current source pull-up at RUN/SS sets the signed to typically drive up to 10,000pF of gate capacitance. turn-on time at approximately 300ms/µF. If both RUN/SS and REGILM are pulled low, the LTC1704 enters shutdown
SW (Pin 2):
Switcher Controller Switching Node. Connect mode. SW to the switching node of the main converter. The TG driver ground returns to SW, providing floating gate drive
COMP (Pin 5):
Switcher Controller Loop Compensation. to the top N-channel MOSFET, QT. The voltage at SW is The COMP pin is connected directly to the output of the compared to IMAX by the current limit comparator while switcher controller’s error amplifier and the input to the the bottom MOSFET, QB is on. The Burst comparator PWM comparator. Use an RC network between the COMP (BURST, see Block Diagram) monitors the potential at SW pin and the FB pin to compensate the feedback loop for and switches to Burst Mode operation under light load optimum transient response. conditions.
FB (Pin 6):
Switcher Controller Feedback Input. FB should
IMAX (Pin 3):
Switcher Controller Current Limit Set. The be connected through a resistor divider network to VOUTSW IMAX pin sets the current limit comparator threshold for to set the switcher output voltage. Also, connect the the switcher controller. If the voltage drop across the switcher loop compensation network to FB. bottom MOSFET, QB, exceeds the magnitude of the volt-
REGDR (Pin 7):
Linear Regulator Controller Driver Output. age at IMAX, the switcher controller enters current limit. Connect REGDR to the base of the external NPN Pass The IMAX pin has an internal 10µA current source pull-up, transistor. The REGILM pin input current controls the allowing the current threshold to be set with a single linear regulator controller maximum driving capability. external resistor to PGND. Kelvin connect this current setting resistor to the source of QB. Refer to the Current
GND (Pin 8):
Signal Ground. All internal low power cir- Limit Programming section for more information on choos- cuitry returns to the GND pin. Connect to a low impedance ing R ground, separated from the PGND node. All feedback, IMAX. 1704bfa 7