LTC1439 Linear Technology, LTC1439 Datasheet - Page 8

• Manufacturer Part Number: LTC1439
• Description: Dual High Efficiency/ Low Noise/ Synchronous Step-Down Switching Regulators
• Manufacturer: Linear Technology

LTC1438/LTC1439
PIN
SENSE
Comparator. Built-in offsets between SENSE
SENSE
trip threshold (same for second controller).
V
age either from the output directly or from an external
resistive divider across the output. The V
mines which point V
V
quires an external resistive divider to set the output
voltage.
V
for Output Voltage Sensing. The voltage sensing for thefirst
controller is internally connected to SENSE
V
controller. For V
set for an output voltage of 3.3V. With V
V
voltage of 5V. Leaving V
voltage of the second controller to be set by an external
resistive divider connected to V
C
the operating frequency.
I
sociated current comparator threshold increases with this
control voltage.
RUN/SS1, RUN/SS2: Combination of Soft Start and Run
Control Inputs. A capacitor to ground at each of these pins
sets the ramp time to full current output. The time is
approximately 0.5s/ F. Forcing either of these pins below
1.3V causes the IC to shut down the circuitry required for
that particular controller. Forcing both of these pins below
1.3V causes the device to shut down completely. For
applications which require 5V keep-alive, refer to the
LTC1538-AUX/LTC1539.
TGL1, TGL2: High Current Gate Drives for Main Top
N-Channel MOSFET. These are the outputs of floating
drivers with a voltage swing equal to INTV
posed on the switch node voltage SW1 and SW2.
TGS1, TGS2: Gate Drives for Small Top N-Channel
MOSFET. These are the outputs of floating drivers with a
voltage swing equal to INTV
8
TH1
OSENSE1,2
OSENSE1
PROG1
OSENSE2
PROG2
OSC
U
, I
: External capacitor C
TH2
FUNCTIONS
+
+
, V
> V
1 pins in conjunction with R
1, SENSE
: Error Amplifier Compensation Point. Each as-
pin allows for remote sensing for the second
pin, only available on the LTC1438-ADJ, re-
PROG2
U
: Receives the remotely sensed feedback volt-
INTVCC
: Programs Internal Voltage Attenuators
PROG1
/1.5 the divider is set for an output
+
U
2: The (+) Input to Each Current
, V
PROG2
OSENSE2
PROG2
OSC
open (DC) allows the output
from this pin to ground sets
CC
< V
OSENSE2
must connect to. The
superimposed on the
INTVCC
SENSE1
.
PROG2
/3, the divider is
set the current
–
CC
1 while the
pin deter-
superim-
–
PROG1
1 and
,
switch node voltage SW. Leaving TGS1 or TGS2 open
invokes Burst Mode operation for that controller.
BG1, BG2: High Current Gate Drive Outputs for Bottom
N-Channel MOSFETs. Voltage swing at these pins is from
ground to INTV
SFB1: Secondary Winding Feedback Input. This input acts
only on the first controller and is normally connected to a
feedback resistive divider from the secondary winding.
Pulling this pin below 1.19V will force continuous syn-
chronous operation for the first controller. This pin should
be tied to: ground to force continuous operation; INTV
in applications that don’t use a secondary winding; and a
resistive divider from the output in applications using a
secondary winding.
POR2: This output is a drain of an N-channel pull-down.
This pin sinks current when the output voltage of the second
controller drops 7.5% below its regulated voltage and re-
leases 65536 oscillator cycles after the output voltage of the
second controller rises to within –5% value of its regulated
value. The POR2 output is asserted when RUN/SS1 and RUN/
SS2 are both low, independant of the V
functional on the LTC1438X.
LBO: This output is a drain of an N-channel pull-down. This
pin will sink current when the LBI pin goes below 1.19V.
LBI: The (+) input of a comparator which can be used as
a low-battery voltage detector. The (–) input is connected
to the 1.19V internal reference.
PLLIN: External Synchronizing Input to Phase Detector.
This pin is internally terminated to SGND with 50k . Tie
this pin to SGND in applications which do not use the
phase-locked loop.
PLL LPF: Output of Phase Detector and Control Input of
Oscillator. Normally a series RC lowpass filter network is
connected from this pin to ground. Tie this pin to SGND in
applications which do not use the phase-locked loop. Can
be driven by a 0V to 2.4V logic signal for a frequency
shifting option.
AUXFB: Feedback Input to the Auxiliary Regulator/Com-
parator. When used as a linear regulator, this input can
either be connected to an external resistive divider or
directly to the collector of the external PNP pass device for
CC
.
OUT2
. This pin is not
CC