LT1673 LINER [Linear Technology], LT1673 Datasheet - Page 18

• Manufacturer Part Number: LT1673
• Description: Auto-Polarity, Ultralow Voltage Step-Up Converter
• Manufacturer: LINER [Linear Technology]

LTC3109
APPLICATIONS INFORMATION
The time for V
calculated by the formula below, which assumes V
programmed to 3.3V and C
With 150μA of charge current available and 5μA of load on
both V
tion after the initial application of power would be 7.81
seconds.
DESIGN EXAMPLE 2
In most pulsed-load applications, the duration, magnitude
and frequency of the load current pulses are known and
fi xed. In these cases, the average charge current required
from the LTC3109 to support the average load must be
calculated, which can be easily done by the following:
where I
to the external circuitry in-between load pulses, including
output capacitor leakage, I
during the pulse, t
and T is the pulse period (essentially the time between
load pulses).
18
I
t
CHG
VOUT
OUT
Q
≥ I
is the sleep current supplied by V
=
Q
and VLDO, the time for V
I
+
CHG
I
OUT
3.3V • 330μF
PULSE
– I
PULSE
to charge and reach regulation can be
VOUT
• t
T
PULSE
is the duration of the load pulse
– I
PULSE
LDO
OUT
is 330μF:
+ t
is the total load current
LDO
OUT
to reach regula-
OUT
and V
OUT
LDO
is
In this example, I
and T is one hour. The average charge current required
from the LTC3109 would be:
Therefore, if the LTC3109 has an input voltage that allows
it to supply a charge current greater than just 5.14μA, the
application can support 100mA pulses lasting 5ms every
hour. It can be seen that the sleep current of 5μA is the
dominant factor in this example, because the transmit
duty cycle is so small (0.00014%). Note that for a V
of 3.3V, the average power required by this application is
only 17μW (not including converter losses).
Keep in mind that the charge current available from the
LTC3109 has no effect on the sizing of the V
and the V
allowed pulse rate.
I
CHG
≥ 5μA +
OUT
capacitor has no effect on the maximum
100mA • 0.005sec
Q
is 5μA, I
3600sec
PULSE
is 100mA, t
= 5.14μA
OUT
PULSE
capacitor,
is 5ms
3109fa
OUT