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LTC3601IUD#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26
LTC3601
7
3601fc
For more information www.linear.com/LTC3601
PIN FUNCTIONS
(QFN/MSE)
MODE/SYNC (Pin 1/Pin 15): Mode Selection and External
Synchronization Input Pin. This pin places the LTC3601
into forced continuous operation when tied to ground.
High efficiency Burst Mode operation is enabled by either
floating this pin or by tying this pin to INTV
CC
. When driven
with an external clock, an internal phase-locked loop will
synchronize the phase and frequency of the internal oscil-
lator to that of the incoming clock signal. During external
clock synchronization, the LTC3601 will default to forced
continuous operation.
PGOOD (Pin 2/Pin 16): Open-Drain Power Good Output
Pin. PGOOD is pulled to ground when the voltage at the
FB pin is not within 8% (typical) of the internal 0.6V refer-
ence. PGOOD becomes high impedance once the voltage
at the FB pin returns to within ±5% (typical) of the internal
reference.
SW (Pins 3, 4/Pins 1, 2): Switch Node Output Pin. Con-
nect this pin to the SW side of the external inductor. The
normal operation voltage swing of this pin ranges from
ground to PV
IN
.
BOOST (Pin 6/Pin 5): Boosted Floating Driver Supply
Pin. The (+) terminal of the external 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 7/Pin 6): Internal 3.3V Regulator Output Pin.
This pin should be decoupled to PGND with a low ESR
ceramic capacitor of 1µF or more.
V
ON
(Pin 8/Pin 7): On-Time Voltage Input Pin. This pin
sets the voltage trip point for the on-time comparator.
Connect this pin to the regulated output to make the on-
time proportional to the output voltage when V
OUT
≤ 6V. If
V
OUT
> 6V, switching frequency may become higher than
the set frequency. The pin impedance is normally 180kΩ.
SGND (Pin 9/Exposed Pad Pin 17): Signal Ground Pin.
This pin should have a low noise connection to reference
ground. The feedback resistor network, external compen-
sation network and RT resistor should be connected to
this ground. In the MSE package, the exposed pad must
be soldered to the PCB to provide a good thermal contact
to the PCB.
RT (Pin 10/Pin 8): Oscillator Frequency Program Pin.
Connect an external resistor, between 80k to 400k, from
this pin to SGND to program the LTC3601 switching fre-
quency from 800kHz to 4MHz. When RT is tied to INTV
CC
,
the switching frequency will default to 2MHz.
FB (Pin 11/Pin 9): Output Voltage Feedback Pin. Input to
the error amplifier that compares the feedback voltage to
the internal 0.6V reference voltage. Connect this pin to
the appropriate resistor divider network to program the
desired output voltage.
ITH (
Pin 12/Pin 10): Error Amplifier Output and Switching
Regulator Compensation Pin. Connect this pin to appro-
priate external components to compensate the regulator
loop frequency response. Connect this pin to INTV
CC
to
use the default internal compensation.
TRACK (Pin 13/Pin 11): Output Voltage Tracking and Soft-
Start Input Pin. Forcing a voltage below 0.6V on this pin
overrides the internal reference input to the error amplifier.
The LTC3601 will servo the FB pin to the TRACK voltage
under this condition. 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 an external capacitor between this pin and
ground. See Applications Information section for more
details.
RUN (Pin 14/Pin 12): Regulator Enable Pin. Enables chip
operation by applying a voltage above 1.25V. A voltage
below 1V on this pin places the part into shutdown. Do
not float this pin.
V
IN
(Pins 15, 16/Pins 13, 14): Main Power Supply Input
Pins. These pins should be closely decoupled to PGND
with a low ESR capacitor of 10µF or more.
PGND (Exposed Pad Pin 17/Pins 3, 4): Power Ground Pin.
The (–) terminal of the input bypass capacitor, C
IN
, and the
(–) terminal of the output capacitor, C
OUT
, should be tied
to this pin with a low impedance connection. In the QFN
package the exposed pad must be soldered to the PCB to
provide low impedance electrical contact to ground and
good thermal contact to the PCB.
LTC3601
8
3601fc
For more information www.linear.com/LTC3601
FUNCTIONAL BLOCK DIAGRAM
–
++
–
+
–
+
V
IN
V
IN
15k
Q6
RUN
SWITCH
LOGIC
AND
ANTI-
SHOOT
THROUGH
BG
ON
Q1
Q2
0.48V 1.25V
RUN
EA
INTERNAL
SOFT-START
SS
Q4
TRACK
C
SS
3605 BD
SGND
R2
R1
RUN
PGND
PGOOD
INTV
CC
FB
SW
TG
V
IN
C
IN
BOOST
SENSE
+
SENSE
–
–
+
–
+
OV
0.648V
–
+
0.3V
FOLDBACK
FOLDBACK
DISABLED
AT START-UP
UV
0.552V
180k
V
ON
V
ON
INT
VCC
M2
M1
L1
C
OUT
INTV
CC
ITH
R
C
C
C1
C
VCC
C
BOOST
–
+
–
+
1.4µA
I
THB
I
CMP
I
REV
3.3V
REG
I
ON
CONTROLLER
OSC
PLL-SYNC
OSC
R
0.6V
REF
S Q
I
ON
MODE/SYNC
R
RT
RT
t
ON
=
V
VON
I
ION
A
V
= 1
6V
LTC3601
9
3601fc
For more information www.linear.com/LTC3601
OPERATION
The LTC3601 is a current mode, monolithic, step-down
regulator capable of providing up to 1.5A of output current.
Its unique controlled on-time architecture allows extremely
low step-down ratios while maintaining a constant switch-
ing frequency. Part operation is enabled by raising the
voltage on the RUN pin above 1.25V nominally.
Main Control Loop
In normal operation the internal top power MOSFET is
turned on for a fixed interval determined by an internal
one-shot timer (“ON” signal in the Block Diagram). When
the top power MOSFET turns off, the bottom power MOS-
FET turns on until the current comparator, I
CMP
, trips,
thus restarting the one-shot timer and initiating the next
cycle. The inductor current is monitored by sensing the
voltage drop across the SW and PGND nodes of the bot-
tom power MOSFET. The voltage at the ITH pin sets the
I
CMP
comparator threshold corresponding to the induc-
tor valley current. The error amplifier EA adjusts this ITH
voltage by comparing an internal 0.6V reference to the
feedback signal, V
FB
, derived from the output voltage. If, for
example, the load current increases, the feedback voltage
will decrease relative to the internal 0.6V reference. The
ITH voltage then rises until the average inductor current
matches that of the load current.
The operating frequency is determined by the value of the
RT resistor, which programs the current for the internal
oscillator. An internal phase-locked loop servos the switch-
ing regulator on-time to track the internal oscillator edge
and force a constant switching frequency. A clock signal
can be applied to the SYNC/MODE pin to synchronize the
switching frequency to an external source. The regulator
defaults to forced continuous operation once the clock
signal is applied.
At low load currents the inductor current can drop to zero
or become negative. If the LTC3601 is configured for
Burst Mode operation, this inductor current condition is
detected by the current reversal comparator, I
REV
, which
in turn shuts off the bottom power MOSFET and places
the part into a low quiescent current sleep state resulting
in discontinuous operation and increased efficiency at low
load currents. Both power MOSFETs will remain off with
the part in sleep and the output capacitor supplying the
load current until the ITH voltage rises sufficiently to initiate
another cycle. Discontinuous operation is disabled by tying
the MODE/SYNC pin to ground placing the LTC3601 into
forced continuous mode. During forced continuous mode,
continuous synchronous operation occurs regardless of
the output load current.
“Power Good” Status Output
The PGOOD open-drain output will be pulled low if the
regulator output exits a ±8% window around the regulation
point. This condition is released once regulation within
a 5% window is achieved. To prevent unwanted PGOOD
glitches during transients or dynamic V
OUT
changes, the
LTC3601 PGOOD falling edge includes a filter time of ap-
proximately 40µs.
V
IN
Overvoltage Protection
In order to protect the internal power MOSFET devices
against transient voltage spikes, the LTC3601 constantly
monitors the V
IN
pin for an overvoltage condition. When
V
IN
rises above 17.5V, the regulator suspends operation
by shutting off both power MOSFETs. Once V
IN
drops
below 16.5V, the regulator immediately resumes normal
operation. The regulator does not execute its soft-start
function when exiting an overvoltage condition.
Short-Circuit Protection
Foldback current limiting is provided in the event the
output is inadvertently shorted to ground. During this
condition the internal current limit (I
LIM
) will be lowered
to approximately one-third its normal value. This feature
reduces the heat dissipation in the LTC3601 during short-
circuit conditions and protects both the IC and the input
supply from any potential damage.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26

LTC3601IUD#TRPBF

Mfr. #:
Buy LTC3601IUD#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 1.5A, 15V, 4MHz Monolithic Synchronous Step-Down Regulator in 3x3 QFN
Lifecycle:
New from this manufacturer.
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