Ultralow Voltage Step-Up Converter and Power Manager ( 20 Page)
In a typical application, a storage capacitor (typically a few
hundred microfarads) is connected to V
. As soon as
VAUX exceeds 2.5V, the V
capacitor will be allowed to
charge up to its regulated voltage. The current available to
charge the capacitor will depend on the input voltage and
transformer turns ratio, but is limited to about 4mA.
A power good comparator monitors the V
The PGD pin is an open-drain output with a weak pull-up
(1MΩ) to the LDO voltage. Once V
7% of its regulated voltage, the PGD output will go high.
drops more than 9% from its regulated voltage,
PGD will go low. The PGD output is designed to drive a
microprocessor or other chip I/O and is not intended to
drive a higher current load such as an LED. Pulling PGD
up externally to a voltage greater than VLDO will cause a
small current to be sourced into VLDO. PGD can be pulled
low in a wire-OR conﬁguration with other circuitry.
is an output that can be turned on and off by the
host, using the V
pin. When enabled, V
connected to V
through a 1.3Ω P-channel MOSFET
switch. This output, controlled by a host processor, can
be used to power external circuits such as sensors and
ampliﬁers, that do not have a low power sleep or shutdown
can be used to power these circuits only
when they are needed.
Minimizing the amount of decoupling capacitance on
will allow it to be switched on and off faster, allowing
shorter burst times and, therefore, smaller duty cycles in
pulsed applications such as a wireless sensor/transmit-
ter. A small V
capacitor will also minimize the energy
that will be wasted in charging the capacitor every time
has a soft-start time of about 5μs to limit capacitor
charging current and minimize glitching of the main output
is enabled. It also has a current limiting circuit
that limits the peak current to 0.3A typical.
enable input has a typical threshold of 1V
with 100mV of hysteresis, making it logic-compatible. If
(which has an internal pull-down resistor) is
will be off. Driving V
high will turn on
Note that while V
is high, the current limiting cir-
cuitry for V
draws an extra 8μA of quiescent current
. This added current draw has a negligible effect
on the application and capacitor sizing, since the load on
output, when enabled, is likely to be orders of
magnitude higher than 8μA.
The VSTORE output can be used to charge a large storage
capacitor or rechargeable battery after V
regulation. Once V
has reached regulation, the VSTORE
output will be allowed to charge up to the VAUX voltage.
The storage element on VSTORE can 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
and LDO outputs. If VAUX drops below VSTORE,
the LTC3108 will automatically draw current from the stor-
age element. Note that it may take a long time to charge
a large capacitor, depending on the input energy available
and the loading on V
Since the maximum current from VSTORE is limited to a
few milliamps, it can safely be used to trickle-charge NiCd
or NiMH rechargeable batteries for energy storage when
the input voltage is lost. Note that the VSTORE capacitor
cannot supply large pulse currents to V
. Any pulse load
must be handled by the V
All outputs of the LTC3108 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: time not to scale.
Sponsor of Alldatasheet
Alldistributor will be your best source to find out the prices for your daily purchasing of Electronic Components.
World wide Buy/Sell Semiconductor & Electronic components on-line marketplace for Brokers and Distributors.
Korean Buy/Sell Semiconductor & Electronic components on-line marketplace for Brokers and Distributors.
Chinese Marketplace to Buy/Sell Semiconductor Electronic components on-line for Brokers and Distributors.
Japanese Buy/Sell Semiconductor & Electronic components on-line marketplace for Brokers and Distributors.
Does ALLDATASHEET help your business so far?
[ DONATE ]
All Rights Reserved©
2003 - 2013
|   Chinese :
| German :
| Japanese :
| Russian :
| Spanish :
| French :
| Italian :
| Portuguese :
| Polish :