Datasheet
LTC3838
12
3838fa
SW1, SW2 (Pins 21, 30/Pins 25, 34): Switch Node Con-
nection to Inductors. Voltage swings are from a diode
voltage below ground to V
IN
. The (–) terminal of the
bootstrap capacitor, C
B
, connects to this node.
BG1, BG2 (Pins 22, 29/Pins 26, 33): Bottom Gate
Driver Outputs. The BG pins drive the gates of the bottom
N-channel power MOSFET between PGND and DRV
CC
.
DRV
CC1
, DRV
CC2
(Pins 23, 28/Pins 27, 32): Supplies of
Bottom Gate Drivers. DRV
CC1
is also the output of an internal
5.3V regulator. DRV
CC2
is also the output of the EXTV
CC
switch. Normally the two DRV
CC
pins are shorted together
on the PCB, and decoupled to PGND with a minimum of
4.7µF ceramic capacitor, C
DRVCC
.
V
IN
(Pin 24/Pin 28): Input Voltage Supply. The supply
voltage can range from 4.5V to 38V. For increased noise
immunity decouple this pin to SGND with an RC filter.
Voltage at this pin is also used to adjust top gate on-time,
therefore it is recommended to tie this pin to the main
power input supply through an RC filter.
PGND (Pin 25, Exposed Pad Pin 39/Pin 29, Exposed
Pad Pin 39): Power Ground. Connect this pin as close
as practical to the source of the bottom N-channel power
MOSFET, the (–) terminal of C
DRVCC
and the (–) terminal
of C
IN
. Connect the exposed pad and PGND pin to SGND
pin using a single PCB trace under the IC. The exposed
pad must be soldered to the circuit board for electrical
and rated thermal performance.
PIN FUNCTIONS
(QFN/TSSOP)
INTV
CC
(Pin 26/Pin 30): Supply Input for Internal Circuitry
(Not Including Gate Drivers). Normally powered from the
DRV
CC
pins through a decoupling RC filter to SGND (typi-
cally 2 and 1µF).
EXTV
CC
(Pin 27/Pin 31): External Power Input. When
EXTV
CC
exceeds the switchover voltage (typically 4.6V),
an internal switch connects this pin to DRV
CC2
and shuts
down the internal regulator so that INTV
CC
and gate driv-
ers draw power from EXTV
CC
. The V
IN
pin still needs to
be powered up but draws minimum current.
V
FB2
(Pin 38/Pin 4): Error Amplifier Feedback Input for
Channel 2. This pin connects the error amplifier to an
external feedback resistor divider from V
OUT2
. In nominal
operation the LTC3838 will attempt to regulate the V
OUT2
to 0.6V divided by the feedback resistor divider ratio.
Shorting this pin to INTV
CC
will disable Channel 2’s er-
ror amplifier, and internally connect ITH2 to ITH1. (As a
result, TRACK/SS2 is no longer functional and PGOOD2
is always pulling low.) By doing so, this part can function
as a dual phase, single V
OUT
step-down controller, and
the two channels use a single Channel1’s error amplifier
for the ITH output and compensation.