LTC3855 LINER [Linear Technology], LTC3855 Datasheet - Page 12

• Manufacturer Part Number: LTC3855
• Description: Dual, Fast, Accurate Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

LTC3838
PIN FUNCTIONS
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
bootstrap capacitor, C
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
DRV
Bottom Gate Drivers. DRV
5.3V regulator. DRV
switch. Normally the two DRV
on the PCB, and decoupled to PGND with a minimum of
4.7μF ceramic capacitor, C
V
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
of C
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.
12
IN
IN
(Pin 24/Pin 28): Input Voltage Supply. The supply
CC1
. Connect the exposed pad and PGND pin to SGND
, DRV
CC2
(Pins 23, 28/Pins 27, 32): Supplies of
CC2
B
, connects to this node.
is also the output of the EXTV
CC1
DRVCC
(QFN/TSSOP)
is also the output of an internal
IN
CC
DRVCC
. The (–) terminal of the
pins are shorted together
.
and the (–) terminal
CC
.
CC
INTV
(Not Including Gate Drivers). Normally powered from the
DRV
cally 2Ω and 1μF).
EXTV
EXTV
an internal switch connects this pin to DRV
down the internal regulator so that INTV
ers draw power from EXTV
be powered up but draws minimum current.
V
Channel 2. This pin connects the error amplifier to an
external feedback resistor divider from V
operation the LTC3838 will attempt to regulate the V
to 0.6V divided by the feedback resistor divider ratio.
Shorting this pin to INTV
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
the two channels use a single Channel 1’s error amplifier
for the ITH output and compensation.
FB2
CC
CC
CC
CC
(Pin 38/Pin 4): Error Amplifier Feedback Input for
pins through a decoupling RC filter to SGND (typi-
(Pin 26/Pin 30): Supply Input for Internal Circuitry
exceeds the switchover voltage (typically 4.6V),
(Pin 27/Pin 31): External Power Input. When
CC
OUT
CC
will disable Channel 2’s er-
. The V
step-down controller, and
IN
pin still needs to
CC
OUT2
and gate driv-
CC2
. In nominal
and shuts
OUT2
3838fa