MCP16251 One-Cell Boost Converter with External UVLO Circuit
DS50002561A-page 16
2017 Microchip Technology Inc.
2.1.2
Short Battery Considerations Overview
Although the marking on an alkaline battery will show 1.5V, the Open-Circuit Voltage
(OCV) can be as high as 1.7V. The Closed Circuit Voltage (CCV), or operating voltage,
will always be smaller than the OCV because of non-idealities in the cell
(i.e., the internal resistance). Both the OCV and CCV vary with battery chemistry,
State-of-Charge (SOC) and discharge rate.
The difference between the OCV and CCV is a function of current flow and internal
resistance. When the load is removed, the battery voltage starts recovering slowly. At
this state, the OCV can reach the nominal value, but a nearly depleted battery will not
be capable of maintaining this voltage once the load is applied.
The internal resistance of a battery is not constant over its life span or
charging/discharging cycles. As a battery discharges, its internal resistance gets
higher, limiting the power that can be supplied to the load. The internal resistance also
varies with battery chemistry, drain rate, battery age and temperature.
Discharging the battery below the OEM recommended cut-off voltage will increase the
cell’s internal resistance. For an alkaline cell, this is 0.8-0.9V. For applications that are
battery-powered, an Undervoltage Lockout (UVLO) solution is recommended, because
after a good start-up, as shown in
Table 1-1
, Microchip’s single cell Boost Converters
can operate from an input voltage as low as 0.35V.
FIGURE 2-2:
Typical Discharge Profile for an AA Alkaline Cell – Battery
Voltage and Internal Resistance.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
0
10
20
30
40
50
60
Internal Resistance
(
ȍ
)
C
ell V
o
ltag
e
(V)
Run Time (h)
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