LTC3879 Linear Technology Corporation, LTC3879 Datasheet - Page 8

• Manufacturer Part Number: LTC3879
• Description: Wide Operating Range No RSENSE Step-Down Controller
• Manufacturer: Linear Technology Corporation

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PIN FUNCTIONS
LTC3879
TRACK/SS (Pin 1): External Tracking and Soft-Start Input.
The LTC3879 regulates V
voltage on the TRACK/SS pin. An internal 1μA pull-up
current source is connected to this pin. A capacitor to
ground at this pin sets the ramp time to the fi nal regulated
output voltage. Alternatively, a resistor divider on another
voltage supply connected to this pin allows the output to
track the other supply during start-up.
PGOOD (Pin 2): Power Good Output. This open-drain
logic output is pulled to ground when the output voltage is
outside of a ±10% window around the regulation point.
V
mum allowed bottom MOSFET V
SW and PGND is equal to (0.133)V
to V
tied to SGND, the device operates with a maximum valley
current sense threshold of 30mV typical. If V
to INTV
current sense threshold of 75mV typical.
MODE (Pin 4): MODE Input. Connect this pin to INTV
enable discontinuous mode for light load operation. Con-
nect 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.
V
nects the error amplifi er to an external resistive divider
from V
8
TH
ON
RNG
IN
FB
(Pin 5): Current Control Threshold and Error Amplifi er
to this pin to set the one-shot timer current and thus
RNG
(Pin 7): On-Time Current Input. Tie a resistor from
(Pin 8): Error Amplifi er Feedback Input. This pin con-
(Pin 3): V
OUT
CC
can be any value between 0.2V and 2V. If V
.
, the device operates with a maximum valley
DS
Sense Voltage Range Input. The maxi-
FB
to the smaller of 0.6V or the
DS
RNG
sense voltage between
. The voltage applied
RNG
is tied
RNG
CC
to
is
RUN (Pin 9): Run Control Input. RUN below 1.5V disables
switching by forcing TG and BG low. RUN less than 1.5V
but greater than 0.7V enables all internal bias including
the INTV
and places the LTC3879 into micropower shutdown mode
of approximately 18μA. There is an internal 1.2μA pull-up
current source for operation with an open-collector RUN
signal.
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
Exposed Pad (Pin 17): The Exposed Pad is SGND and
must be soldered to the PCB.
IN
IN
(Pin 10): Main Input Supply. The supply voltage can
+ (INT
VIN
CC
.
(Pin 11): Internal 5.3V Regulator Output. The
CC
CC
VCC
B
.
output. RUN below 0.7V shuts down all bias
, connects to this node. This pin swings from
– V
SCHOTTKY
).
INTVCC
and the (–) terminal
CC
IN
B
, connects to this
.
– V
SCHOTTKY
) to
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