Datasheet

LTC3633A-2/LTC3633A-3
9
3633a23f
(QFN/TSSOP)
PIN FUNCTIONS
BOOST2 (Pin 17/Pin 20): Boosted Floating Driver Supply
for Channel 2. 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 PV
IN
+INTV
CC
.
INTV
CC
(Pin 18/Pin 21): 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 19/Pin 22): 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 PV
IN
+ INTV
CC
.
SV
IN
(Pin 20/Pin 23): Signal Input Supply. This pin powers
the internal control circuitry. The internal LDO for INTV
CC
is powered from this pin.
PV
IN1
(Pins 21, 22/Pins 24, 25): Power Supply Input for
Channel 1. Input voltage to the on chip power MOSFETs
on channel 1.
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 PV
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-2,
1.5V – 12V for LTC3633A-3). When V
OUT
is outside the
V
ON
sense range, the switching frequency may deviate
from the programmed frequency. The pin impedance is
nominally 140k.
ITH1 (Pin 26/Pin 1): Channel 1 Error Amplifi er 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
amplifi er. The LTC3633A-2 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
amplifi er. An internal 1.4µA pull up current from INTV
CC
allows a soft-start function to be implemented by connect-
ing a capacitor between this pin and SGND.
V
FB1
(Pin 28/Pin 3): Channel 1 Output Feedback Voltage
Pin. Input to the error amplifi er 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.