LTC3835-1 Linear Technology, LTC3835-1 Datasheet - Page 7

• Manufacturer Part Number: LTC3835-1
• Description: Low IQ Synchronous Step-Down Controller
• Manufacturer: Linear Technology

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PIN FUNCTIONS
PLLLPF (Pin 1/Pin 1): The phase-locked loop’s lowpass fi lter
is tied to this pin when synchronizing to an external clock.
Alternatively, tie this pin to GND, INTV
select 250kHz, 530kHz or 400kHz switching frequency.
I
Regulator Compensation Points. The current comparator
trip point increases with this control voltage.
TRACK/SS (Pin 3/Pin 3): External Tracking and Soft-Start
Input. The LTC3835-1 regulates the V
of 0.8V or the voltage on the TRACK/SS pin. A internal 1μA
pull-up current source is connected to this pin. A capacitor
to ground at this pin sets the ramp time to fi nal regulated
output voltage. Alternatively, a resistor divider on another
voltage supply connected to this pin allows the LTC3835-1
output to track the other supply during start-up.
V
age from an external resistive divider across the output.
SGND (Pin 5/Pin 5): Small-Signal Ground. Must be routed
separately from high current grounds to the common (–)
terminals of the input capacitor.
PGND (Pin 6/Pin 6): Driver Power Ground. Connects to the
source of bottom (synchronous) N-channel MOSFET, anode
of the Schottky rectifi er and the (–) terminal of C
TYPICAL PERFORMANCE CHARACTERISTICS
TH
FB
(Pin 2/Pin 2): Error Amplifi er Outputs and Switching
(Pin 4/Pin 4): Receives the remotely sensed feedback volt-
4.2
4.1
4.0
3.9
3.8
3.7
3.6
3.5
3.4
3.3
3.2
–45
Undervoltage Lockout Threshold
vs Temperature
–30
–15
TEMPERATURE (°C)
0
RISING
FALLING
15
30
45
(DHC Package/GN Package)
60
75
38351 G25
FB
90
CC
voltage to the smaller
or leave fl oating to
400
396
392
404
402
398
394
5
Oscillator Frequency
vs Input Voltage
IN
10
.
INPUT VOLTAGE (V)
15
20
BG (Pin 7/Pin 7): High Current Gate Drive for Bottom
(Synchronous) N-Channel MOSFET. Voltage swing at this
pin is from ground to INTV
INTV
Dropout Regulator. The driver and control circuits are
powered from this voltage source. Must be decoupled to
power ground with a minimum of 4.7μF tantalum or other
low ESR capacitor.
V
should be tied between this pin and the signal ground pin.
SW (Pin 10/Pin 10): Switch Node Connections to Inductor.
Voltage swing at this pin is from a Schottky diode (external)
voltage drop below ground to V
TG (Pin 11/Pin 11): High Current Gate Drive for Top
N-Channel MOSFET. These are the outputs of fl oating drivers
with a voltage swing equal to INTV
on the switch node voltage SW.
BOOST (Pin 12/Pin 12): Bootstrapped Supply to the Topside
Floating Driver. A capacitor is connected between the
BOOST and SW pins and a Schottky diode is tied between
the BOOST and INTV
pin is from INTV
IN
(Pin 9/Pin 9): Main Supply Pin. A bypass capacitor
25
CC
(Pin 8/Pin 8): Output of the Internal Linear Low
30
T
38351 G26
A
= 25°C, unless otherwise noted.
35
CC
to (V
CC
12
10
pins. Voltage swing at the BOOST
8
6
4
0
2
IN
–45
Shutdown Current
vs Temperature
+ INTV
CC
–30
.
–15
IN
CC
CC
.
TEMPERATURE (°C)
0
LTC3835-1
– 0.5V superimposed
).
15
30
45
60
75
38351 G27
38351fc
7
90