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LTC3109

3109fa

on the application and capacitor sizing, since the load on

the VOUT2 output, when enabled, is likely to be orders of

magnitude higher than 8μA.

VSTORE

The VSTORE output can be used to charge a large storage

capacitor or rechargeable battery. Once VOUT has reached

regulation, the VSTORE output will be allowed to charge

up to the clamped VAUX voltage (5.25V typical). The

storage element on VSTORE can then be used to power

the system in the event that the input source is lost, or

is unable to provide the current demanded by the VOUT,

VOUT2 and LDO outputs.

If VAUX drops below VSTORE, the LTC3109 will automati-

cally draw current from the storage element. Note that it

may take a long time to charge a large storage capacitor,

depending on the input energy available and the loading

on VOUT and VLDO.

Since the maximum charging current available at the

VSTORE output is limited to about 15mA, it can safely be

used to trickle charge NiCd or NiMH batteries for energy

storage when the input voltage is lost.

Note that VSTORE is not intended to supply high pulse

load currents to VOUT. Any pulse load on VOUT must be

handled by the VOUT reservoir capacitor.

Short-Circuit Protection

All outputs of the LTC3109 are current limited to protect

against short circuits to ground.

Output Voltage Sequencing

A timing diagram showing the typical charging and voltage

sequencing of the outputs is shown in Figure 1. Note that

the horizontal (time) axis is not to scale, and is used for

illustration purposes to show the relative order in which

the output voltages come up.

OPERATION (Refer to the Block Diagram)

5.0

VSTORE

PGOOD

VOUT

VLDO

3.0

2.0

1.0

3.0

2.0

1.0

2.5

5.0

2.5

010

TIME (ms)

3109 F01

5.0

2.5

VAUX

Figure 1. Output Voltage Sequencing

(with VOUT Programmed for 3.3V). Time Not to Scale

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