LTC3878 Linear Technology Corporation, LTC3878 Datasheet - Page 7

• Manufacturer Part Number: LTC3878
• Description: Wide Operating Range No RSENSE Step-Down Controller
• Manufacturer: Linear Technology Corporation

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PIN FUNCTIONS
RUN/SS (Pin 1): Run Control and Soft-Start Input. A
capacitor to ground on this pin sets the ramp time to full
output current (approximately 3s/μF) when RUN/SS is
open. The switching outputs are disabled when below 1.5V.
The device is in micropower shutdown when under 0.7V.
If left open, there is an internal 1.2μA pull-up current on
RUN/SS. INTV
PGOOD (Pin 2): Power Good Output. This open-drain
logic output is pulled to ground when the output voltage is
outside of a ±7.5% window around the regulation point.
V
mum allowed bottom MOSFET V
SW and PGND is equal to (0.133)V
to V
is tied to SGND, the device operates with a peak sense
voltage that is equivalent to a V
to INTV
that is equivalent to a V
FCB (Pin 4): Forced Continuous Input. Connect this pin
to INTV
operation. Connect this pin to SGND to force continuous
mode operation in all conditions.
I
Compensation Point. The current comparator threshold
increases with this control voltage. The voltage ranges
from 0V to 2.4V, with 0.8V corresponding to zero sense
voltage (zero current).
SGND (Pin 6): Signal Ground. All small-signal components
should be connected to SGND. Connect SGND to PGND
using a single PCB trace.
I
V
the switching frequency.
TH
ON
RNG
IN
(Pin 5): Current Control Threshold and Error Amplifi er
to this pin to set the one-shot timer current and thus
(Pin 7): On-Time Current Input. Tie a resistor from
RNG
(Pin 3): V
CC
CC
can be any value between 0.2V and 2V. If V
, the device operates with a peak sense voltage
to enable discontinuous mode for light load
CC
DS
is enabled when RUN/SS exceeds 0.7V.
Sense Voltage Range Input. The maxi-
RNG
of 1.4V.
RNG
DS
RNG
sense voltage between
of 0.7V. If V
. The voltage applied
RNG
is tied
RNG
V
nects the error amplifi er to an external resistive divider
from V
NC (Pin 9): For factory use only. Can be connected to any
voltage equal to or less than INTV
V
range from 4V to 38V. For increased noise immunity de-
couple this pin to PGND with an RC fi lter.
INTV
driver and control circuits are powered from this voltage.
Decouple this pin to PGND with a minimum of 1μF , 10V
X5R or X7R ceramic capacitor.
BG (Pin 12): Bottom Gate Drive. This pin drives the gate
of the bottom N-Channel power MOSFET between PGND
and INTV
PGND (Pin 13): 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
SW (Pin 14): Switch Node. The (–) terminal of the bootstrap
capacitor, C
a diode voltage below ground up to V
TG (Pin 15): Top Gate Drive. This pin drives the gate of the
top N-channel power MOSFET between SW and BOOST.
BOOST (Pin 16): Boosted Floating Driver Supply. The (+)
terminal of the bootstrap capacitor, C
node. This node swings from (INTV
V
FB
IN
IN
(Pin 10): Main Input Supply. The supply voltage can
+ (INT
(Pin 8): Error Amplifi er Feedback Input. This pin con-
VIN
CC
OUT
.
(Pin 11): Internal 5.3V Regulator Output. The
CC
.
VCC
B
.
, connects to this node. This pin swings from
– V
SCHOTTKY
).
INTVCC
CC
.
and the (–) terminal
CC
IN
B
, connects to this
LTC3878
.
– V
SCHOTTKY
) to
7
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