Datasheet
LTC3109
11
3109fb
For more information www.linear.com/LTC3109
on the application and capacitor sizing, since the load on
the V
OUT2
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 V
OUT
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 V
OUT
,
V
OUT2
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 V
OUT
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 V
OUT
. Any pulse load on V
OUT
must be
handled by the V
OUT
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
V
OUT
VLDO
3.0
2.0
1.0
0
3.0
2.0
1.0
0
2.5
0
5.0
2.5
0
0 10 20 30 40
TIME (ms)
3109 F01
50 60 70 80
5.0
2.5
VOLTAGE (V)
0
VAUX
Figure 1. Output Voltage Sequencing
(with V
OUT
Programmed for 3.3V). Time Not to Scale