LT1674 datasheet(6/24 Pages) LINER

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LTC3109

3109fa

LDO Step Load Response

Enable Input and VOUT2

Running on Storage Capacitor

PIN FUNCTIONS (QFN/SSOP)

VSTORE (Pin 1/Pin 3): Output for the Storage Capacitor or

Battery. A large storage 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.

VAUX (Pin 2/Pin 4): Output of the Internal Rectiﬁer Cir-

cuit and VCC for the IC. Bypass VAUX with at least 1μF of

capacitance to ground. An active shunt regulator clamps

VAUX to 5.25V (typical).

VOUT (Pin 3/Pin 5): 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 a reservoir

capacitor or to a rechargeable battery. Any high current

pulse loads must be fed by the reservoir capacitor on

this pin.

VOUT2 (Pin 4/ Pin 6): Switched Output of the Converter.

Connect this pin to a switched load. This output is open

until VOUT_EN is driven high, then it is connected to VOUT

through a 1Ω PMOS switch. If not used, this pin should

be left open or tied to VOUT.

VOUT2_EN (Pin 5/Pin 7): Enable Input for VOUT2. VOUT2

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.

PGOOD (Pin 6/Pin 8): Power Good Output. When VOUT

is within 7.5% of its programmed value, this pin will be

pulled up to the LDO voltage through a 1M resistor. If

VOUT drops 9% below its programmed value PGOOD will

go low. This pin can sink up to 100μA.

VLDO (Pin 7/Pin 9): 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.

GND (Pins 8, 11, 16, Exposed Pad Pin 21/Pins 10, 13,

18): Ground Pins. Connect these pins directly to the ground

plane. The exposed pad serves as a ground connection and

as a means of conducting heat away from the die.

VS2 (Pin 20/Pin 2): VOUT Select Pin 2. Connect this

pin to ground or VAUX to program the output voltage

(see Table 1).

VS1 (Pin 19/Pin 1): VOUT Select Pin 1. Connect this

pin to ground or VAUX to program the output voltage

(see Table 1).

Table 1. Regulated Output Voltage Using Pins VS1 and VS2

VS2

VS1

VOUT

GND

2.35V

GND

VAUX

3.3V

VAUX

GND

4.1V

VAUX

5.0V

TYPICAL PERFORMANCE CHARACTERISTICS T

A = 25°C, unless otherwise noted.

VLDO

20mV/DIV

ILDO

5mA/DIV

200μs/DIV

3109 G15

0mA TO 3mA LOAD STEP

CLDO = 2.2μF

1ms/DIV

3109 G16

CH2

VOUT2

1V/DIV

CH1

VOUT2_EN

1V/DIV

10mA LOAD ON VOUT2

COUT = 220μF

5SEC/DIV

3109 G17

CH2, VOUT

1V/DIV

CH1, VIN

50mV/DIV

CH3

VSTORE

1V/DIV

CH4, VLDO

1V/DIV

CSTORE = 470μF

VOUT LOAD = 100μA

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