LTC3633A-1_15 Datasheet, PDF (9/30 Pages) Linear Technology – Dual Channel 3A, 20V Monolithic Synchronous Step-Down Regulator

LTC3633A/LTC3633A-1
PIN FUNCTIONS (QFN/TSSOP)
V2P5 (Pin 18/Pin 21): 2.5V Regulator Output. Outputs a
regulated 2.5V supply voltage capable of supplying 10mA.
Bypass this pin with a minimum of 1µF low ESR ceramic
capacitor. Tie this pin to INTV_CC when this output is not
being used in the application.
INTV_CC (Pin 19/Pin 22): Internal 3.3V Regulator Output.
The internal power drivers and control circuits are powered
from this voltage. The internal regulator is disabled when
both channel 1 and channel 2 are disabled with the RUN1/
RUN2 inputs. Decouple this pin to power ground with a
minimum of 1µF low ESR ceramic capacitor.
BOOST1 (Pin 20/Pin 23): Boosted Floating Driver Supply
for Channel 1. The (+) terminal of the bootstrap capacitor
connects to this pin while the (–) terminal connects to
the SW pin. The normal operation voltage swing of this
pin ranges from a diode voltage drop below INTV_CC up
to V_IN + INTV_CC.
V_IN1 (Pins 21,22/Pins 24, 25): Power Supply Input for
Channel 1. Input voltage to the on chip power MOSFETs
on channel 1. The internal LDO for INTV_CC is powered off
of this pin.
SW1 (Pins 23,24/Pins 26, 27): Channel 1 Switch Node
Connection to External Inductor. Voltage swing of SW is
from a diode voltage drop below ground to V_IN.
V_ON1 (Pin 25/Pin 28): On-Time Voltage Input for Chan-
nel 1. This pin sets the voltage trip point for the on-time
comparator. Tying this pin to the regulated output voltage
makes the on-time proportional to V_OUT1 when V_OUT1 is
within the V_ON1 sense range (0.6V – 6V for LTC3633A,
1.5V – 12V for LTC3633A-1). When V_OUT is outside the
V_ON sense range, the switching frequency may deviate
from the programmed frequency. The pin impedance is
nominally 140kΩ.
ITH1 (Pin 26/Pin 1): Channel 1 Error Amplifier Output and
Switching Regulator Compensation Pin. Connect this pin
to appropriate external components to compensate the
regulator loop frequency response. Connect this pin to
INTV_CC to use the default internal compensation.
TRACKSS1 (Pin 27/Pin 2): Output Tracking and Soft-Start
Input Pin for Channel 1. Forcing a voltage below 0.6V on
this pin bypasses the internal reference input to the error
amplifier. The LTC3633A will servo the FB pin to the TRACK
voltage. Above 0.6V, the tracking function stops and the
internal reference resumes control of the error amplifier.
An internal 1.4µA pull up current from INTV_CC allows a
soft-start function to be implemented by connecting a
capacitor between this pin and SGND.
V_FB1 (Pin 28/Pin 3): Channel 1 Output Feedback Voltage
Pin. Input to the error amplifier that compares the feedback
voltage to the internal 0.6V reference voltage. Connect this
pin to a resistor divider network to program the desired
output voltage.
PGND (Exposed Pad Pin 29/Exposed Pad Pin 29): Power
Ground Pin. The (–) terminal of the input bypass capaci-
tor, C_IN, and the (–) terminal of the output capacitor, C_OUT,
should be tied to this pin with a low impedance connec-
tion. This pin must be soldered to the PCB to provide low
impedance electrical contact to power ground and good
thermal contact to the PCB.
For more information www.linear.com/LTC3633A
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