4

LT1309

50

µs/DIV

1309 G08

12V

2V/DIV

10V/DIV

VPP VALID

10V/DIV

50

µs/DIV

1309 G09

5V/DIV

10V/DIV

500mA/DIV

12V OUTPUT

1V/DIV

AC COUPLED

10mA

60mA

50

µs/DIV

1309 G10

PI FU CTIO S

SOFT START (Pin 1): A 0.1

µF/1MΩ parallel RC from this

pin to GND provides a Soft Start function upon device

turn-on. Initially about 80

µA will flow from the pin into the

capacitor. When the voltage at the pin reaches approxi-

mately 0.4V, current ceases flowing out of the pin.

capacitance is required. More capacitance reduces ring-

ing on the supply line.

PGND (Pin 3): Power Ground. Connect to ground plane.

present on this pin. To minimize radiated noise keep

layout short and direct.

GND (Pin 5): Signal Ground. Connect to ground plane.

VPP VALID (Pin 6): This pin provides a logic signal

indicating that output voltage has reached 12V. Active low

with internal 200k pull-up resistor.

SENSE (Pin 7): Output Sense Pin. This pin connects to a

resistive divider that sets the output voltage. In shutdown,

the resistor string is disconnected and current into this pin

reduces to < 1

µA.

ON/OFF (Pin 8): Shutdown Control. When pulled below

1.5V, this pin disables the LT1309 and reduces supply

current to 9

µA. All circuitry is disabled in shutdown. The

part is enabled when ON/OFF is greater than 1.5V.

Load Transient Response,