Datasheet

LTC3838-1
11
38381f
For more information www.linear.com3838-1
V
OUTSENSE1
–
(Pin 13): Differential Output Sense Amplifier
(–) Input of Channel 1. Connect this pin to the negative
terminal of the output load capacitor of V
OUT1
.
SENSE1
+
, SENSE2
+
(Pin 14, Pin 37): Differential Current
Sense Comparator (+) Inputs. The ITH pin voltage and
controlled offsets between the SENSE
+
and SENSE
–
pins
set the current trip threshold. The comparator can be used
for R
SENSE
sensing or inductor DCR sensing. For R
SENSE
sensing, Kelvin (4-wire) connect the SENSE
+
pin to the
(+) terminal of R
SENSE
. For DCR sensing, tie the SENSE
+
pins to the connection between the DCR sense capacitor
and sense resistor tied across the inductor.
SENSE1
–
, SENSE2
–
(Pin 15, Pin 36): Differential Current
Sense Comparator (–) Input. The comparator can be used
for R
SENSE
sensing or inductor DCR sensing. For R
SENSE
sensing,
Kelvin (4-wire) connect the SENSE
–
pin to the (–)
terminal of R
SENSE
. For DCR sensing, tie the SENSE
–
pin
to the DCR sense capacitor tied to the inductor V
OUT
node
connection. These pins also function as output voltage
sense pins for the top MOSFET on-time adjustment. The
impedance looking into these pins is different from the
SENSE
+
pins because there is an additional 500k internal
resistor from each of the SENSE
–
pins to SGND.
DTR1, DTR2 (Pin 16, Pin 35): Detect Load-Release Tran-
sient for Overshoot Reduction. When load current sud-
denly drops, if voltage on this DTR pin drops below half
of INTV
CC
, the bottom gate (BG) could turn off, allowing
the inductor current to drop to zero faster, thus reducing
the V
OUT
overshoot. (Refer to Load-Release Transient
Detection in the Applications Information section for more
details.) An internal 2.5μA current source pulls this pin
toward INTV
CC
. To disable the DTR feature, simply tie the
DTR pin to INTV
CC
.
RUN1, RUN2 (Pin 17, Pin 34): Run Control Inputs. An
internal proportional-to-absolute-temperature (PTAT)
pull-up current source (~1.2µA at 25°C) is constantly
connected to this pin. Taking both RUN1 and RUN2 pins
below a threshold voltage (~0.8V at 25°C) shuts down all
bias of INTV
CC
and DRV
CC
and places the LTC3838-1 into
micropower shutdown mode. Allowing either RUN pin to
rise above this threshold would turn on the internal bias
supply and the circuitry for the particular channel. When
a RUN pin rises above 1.2V, its corresponding channel’s
TG and BG drivers are turned on and
an additional 5µA
temperature-independent pull-up current is connected
internally to the RUN pin. Either RUN pin can sink up to
50µA, or be forced no higher than 6V.
PGOOD1, PGOOD2 (Pin 18, Pin 33): Power Good Indicator
Outputs. This open-drain logic output is pulled to ground
when the output voltage goes out of a ±7.5% window
around the regulation point, after a 50µs power-bad-
masking
delay. Returning to the regulation point, there is
a delay of around 20µs to power good, and a hysteresis
of around 2.5% (or 15mV on the same scale as the 0.6V
reference and internal feedback voltages, V
FB1,2
) on both
sides of the voltage window.
BOOST1, BOOST2 (Pin 19, Pin 32): Boosted Floating
Supplies for Top MOSFET Drivers. The (+) terminal of the
bootstrap capacitor, C
B
, connects to this pin. The BOOST
pins swing by a V
IN
between a diode drop below DRV
CC
,
or (V
DRVCC
– V
D
) and (V
IN
+ V
DRVCC
– V
D
).
TG1, TG2 (Pin 20, Pin 31): Top Gate Driver Outputs. The
TG pins drive the gates of the top N-channel power MOSFET
with a voltage swing of V
DRVCC
between SW and BOOST.
PIN FUNCTIONS