Datasheet

LTC3129-1
9
31291fa
For more information www.linear.com/LTC3129-1
BST1 (Pin 1/Pin 15): Boot-Strapped Floating Supply for
High Side NMOS Gate Drive. Connect to SW1 through a
22nF capacitor, as close to the part as possible. The value
is not critical. Any value from 4.7nF to 47nF may be used.
V
IN
(Pin 2/Pin 16): Input Voltage for the Converter. Connect
a minimum of 4.7µF ceramic decoupling capacitor from
this pin to the ground plane, as close to the pin as possible.
V
CC
(Pin 3/Pin 1): Output Voltage of the Internal Voltage
Regulator. This is the supply pin for the internal circuitry.
Bypass this output with a minimum of 2.2µF ceramic ca
-
pacitor close to the pin. This pin may be back-driven by
an external supply, up to a maximum of 5.5V.
RUN (Pin 4/Pin 2): Input to the Run Comparator. Pull
this pin above 1.1V to enable the V
CC
regulator and above
1.28V to enable the converter. Connecting this pin to a
resistor divider from V
IN
to ground allows programming a
V
IN
start threshold higher than the 1.8V (typical) V
IN
UVLO
threshold. In this case, the typical V
IN
turn-on threshold is
determined by V
IN
= 1.22V • [1+(R3/Pin R4)] (see Figure 2).
MPPC (Pin 5/Pin 3): Maximum
Power Point Control
Programming Pin. Connect this pin to a resistor divider
from V
IN
to ground to enable the MPPC functionality.
If the V
OUT
load is greater than what the power source
can provide, the MPPC will reduce the inductor current
to regulate V
IN
to a voltage determined by: V
IN
= 1.175V
• [1 + (R5/R6)] (see Figure 3). By setting the V
IN
regula-
tion voltage appropriately, maximum power transfer from
the
limited source is assured. Note this pin is very noise
sensitive, therefore minimize trace length and stray capaci
-
tance. Please refer to the Applications Information section
for more detail on programming the MPPC for different
sources. If this function is not needed, tie the pin to V
CC
.
GND (Pin 6/Pin 4): Signal Ground. Provide a short direct
PCB path between GND and the ground plane where the
exposed pad is soldered.
VS3 (Pin 7/Pin 5): Output Voltage Select Pin. Connect this
pin to ground or V
CC
to program the output voltage (see
Table 1). This pin should not float or go below ground.
If this pin is externally driven above V
CC
, a 1M resistor
should be added in series.
VS2 (Pin 8/Pin 6): Output Voltage Select Pin.
Connect this
pin
to ground or V
CC
to program the output voltage (see
Table 1). This pin should not float or go below ground.
VS1 (Pin 9/Pin 7): Output Voltage Select Pin. Connect this
pin to ground or V
CC
to program the output voltage (see
Table 1). This pin should not float or go below ground.
PWM (Pin 10/Pin 8): Mode Select Pin.
PWM = Low (ground): Enables automatic Burst Mode
operation.
PWM = High (tie to V
CC
): Fixed frequency PWM
operation.
This
pin should not be allowed to float. It has internal 5M
pull-down resistor.
PGOOD (Pin 11/Pin 9): Open drain output that pulls to
ground when FB drops too far below its regulated volt
-
age. Connect
a pull-up resistor from this pin to a positive
supply. This pin can sink up to the absolute maximum
rating of 15mA when low. Note that this pin is forced low
in shutdown or V
CC
UVLO.
V
OUT
(Pin 12/Pin 10): Output voltage of the converter, set
by the VS1-VS3 programming pins according to Table 1.
Connect a minimum value of 4.7µF ceramic capacitor from
this pin to the ground plane, as close to the pin as possible.
BST2 (Pin 13/Pin 11): Boot-Strapped
Floating Supply for
High
Side NMOS Gate Drive. Connect to SW2 through a
22nF capacitor, as close to the part as possible. The value
is not critical. Any value from 4.7nF to 47nF may be used
SW2 (Pin 14/Pin 12): Switch Pin. Connect to one side of
the inductor. Keep PCB trace lengths as short and wide
as possible to reduce EMI.
pin FuncTions
(QFN/MSOP)