LTC3633A/LTC3633A-1
PIN FUNCTIONS (QFN/TSSOP)
V2P5 (Pin 18/Pin 21): 2.5V Regulator Output. Outputs a
regulated2.5Vsupplyvoltagecapableofsupplying10mA.
Bypass this pin with a minimum of 1μF low ESR ceramic
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
capacitor. Tie this pin to INTV when this output is not
CC
being used in the application.
INTV to use the default internal compensation.
CC
INTV (Pin 19/Pin 22): Internal 3.3V Regulator Output.
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. TheLTC3633AwillservotheFBpintotheTRACK
voltage. Above 0.6V, the tracking function stops and the
internal reference resumes control of the error amplifier.
CC
Theinternalpowerdriversandcontrolcircuitsarepowered
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.
An internal 1.4μA pull up current from INTV allows a
CC
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
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 ranges from a diode voltage drop below INTV up
Pin.Inputtotheerroramplifierthatcomparesthefeedback
voltagetotheinternal0.6Vreferencevoltage. Connectthis
pin to a resistor divider network to program the desired
output voltage.
CC
to V + INTV .
IN
CC
V
(Pins 21,22/Pins 24, 25): Power Supply Input for
IN1
Channel 1. Input voltage to the on chip power MOSFETs
on channel 1. The internal LDO for INTV is powered off
of this pin.
PGND (Exposed Pad Pin 29/Exposed Pad Pin 29): Power
CC
Ground Pin. The (–) terminal of the input bypass capaci-
tor, C , and the (–) terminal of the output capacitor, C
,
IN
OUT
SW1 (Pins 23,24/Pins 26, 27): Channel 1 Switch Node
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.
Connection to External Inductor. Voltage swing of SW is
from a diode voltage drop below ground to V .
IN
V
(Pin 25/Pin 28): On-Time Voltage Input for Chan-
ON1
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
when V
is
OUT1
OUT1
within the V
sense range (0.6V – 6V for LTC3633A,
ON1
1.5V – 12V for LTC3633A-1). When V
is outside the
OUT
V
sense range, the switching frequency may deviate
ON
from the programmed frequency. The pin impedance is
nominally 140kΩ.
3633a1f
9
Linear [ Linear ]
