LTC3108-1
PIN FUNCTIONS
(DFN/SSOP)
VAUX (Pin 1/Pin 2):
Output of the Internal Rectifier Cir-
cuit and V
CC
for the IC. Bypass VAUX with at least 1μF of
capacitance. An active shunt regulator clamps VAUX to
5.25V (typical).
VSTORE (Pin 2/Pin 3):
Output for the Storage Capacitor
or Battery. A large capacitor may be connected from this
pin to GND for powering the system in the event the input
voltage is lost. It will be charged up to the maximum VAUX
clamp voltage. If not used, this pin should be left open
or tied to VAUX.
V
OUT
(Pin 3/Pin 4):
Main Output of the Converter. The
voltage at this pin is regulated to the voltage selected by
VS1 and VS2 (see Table 1). Connect this pin to an energy
storage capacitor or to a rechargeable battery.
V
OUT2
(Pin 4/Pin 5):
Switched Output of the Converter.
Connect this pin to a switched load. This output is open
until V
OUT2_EN
is driven high, then it is connected to
V
OUT
through a 1.3Ω P-channel switch. If not used, this
pin should be left open or tied to V
OUT
. The peak current
in this output is limited to 0.3A typical.
VLDO (Pin 5/Pin 6):
Output of the 2.2V LDO. Connect a
2.2μF or larger ceramic capacitor from this pin to GND.
If not used, this pin should be tied to VAUX.
PGD (Pin 6/Pin 7):
Power Good Output. When V
OUT
is
within 7.5% of its programmed value, PGD will be pulled
up to VLDO through a 1MΩ resistor. If V
OUT
drops 9%
below its programmed value PGD will go low. This pin
can sink up to 100μA.
VS2 (Pin 7/Pin 10):
V
OUT
Select Pin 2. Connect this pin
to ground or VAUX to program the output voltage (see
Table 1).
VS1 (Pin 8/Pin 11):
V
OUT
Select Pin 1. Connect this pin
to ground or VAUX to program the output voltage (see
Table 1).
V
OUT2_EN
(Pin 9/Pin 12):
Enable Input for V
OUT2
. V
OUT2
will be enabled when this pin is driven high. There is an
internal 5M pull-down resistor on this pin. If not used,
this pin can be left open or grounded.
C1 (Pin 10/Pin 13):
Input to the Charge Pump and Rectifier
Circuit. Connect a capacitor from this pin to the secondary
winding of the step-up transformer.
C2 (Pin 11/Pin 14):
Input to the N-Channel Gate Drive
Circuit. Connect a capacitor from this pin to the secondary
winding of the step-up transformer.
SW (Pin 12/Pin 15):
Drain of the Internal N-Channel
Switch. Connect this pin to the primary winding of the
transformer.
GND (Pins 1, 8, 9, 16) SSOP Only:
Ground
GND (Exposed Pad Pin 13) DFN Only:
Ground. The DFN
exposed pad must be soldered to the PCB ground plane.
It serves as the ground connection, and as a means of
conducting heat away from the die.
Table 1. Regulated Voltage Using Pins VS1 and VS2
VS2
GND
GND
VAUX
VAUX
VS1
GND
VAUX
GND
VAUX
V
OUT
2.5V
3V
3.7V
4.5V
31081fa
7
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
