LTC3109_15 Datasheet, PDF (11/24 Pages) Linear Technology – Auto-Polarity, Ultralow Voltage Step-Up Converter and Power Manager

LTC3109
Operation (Refer to the Block Diagram)
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.
5.0
2.5
VSTORE
0
3.0
2.0
1.0
PGOOD
0
5.0
2.5
V_OUT
0
3.0
2.0
1.0
VLDO
0
5.0
VAUX
2.5
0
0
10
20
30
40
50
60
70
80
TIME (ms)
3109 F01
Figure 1. Output Voltage Sequencing
(with V_OUT Programmed for 3.3V). Time Not to Scale
For more information www.linear.com/LTC3109
3109fb
11