AN-1025 Datasheet, PDF (1/8 Pages) Fairchild Semiconductor – Maximum Power Enhancement Techniques for SuperSOTTM-3 Power MOSFETs

Preliminary
AN-1025
Application Note
Using the EnerChip™ in Pulse Current Applications
Introduction
EnerChips are solid state, reflow solder tolerant batteries packaged in standard surface mount, low profile
packages. They can be placed onto printed circuit boards (PCBs) using high speed pick-and-place equipment
on PCB assembly lines. They are ideal as rechargeable backup power sources for clocks, memories, micro-
controllers and other low power circuits where data or timing information must be retained in the absence of
main system power. EnerChips are also used in wireless sensor and transmitter systems, often operating over
extreme temperature ranges. This Application Note describes methods of improving system performance when
using the EnerChip in applications that require pulse currents greater than the EnerChip’s capability, as when
driving a radio transmitter or receiver in wireless sensor networks. Designing these types of battery powered
systems begins with a characterization of battery performance specifications followed by determining whether
an external boost capacitor might be required.
Background
All batteries have an internal impedance that ultimately limits the peak current that can be drawn from the cell.
Each battery chemistry, design, and manufacturing process has inherent mechanisms and dependencies at
work, resulting in peak currents that vary over temperature, state-of-charge, age of the cell, and other factors.
When the load placed on the battery exceeds the peak current delivery capability of the battery, the power to
the load can be supplemented through the use of an external capacitor as shown in Figure 1. The capacitor
holds very little charge relative to the EnerChip but the low internal resistance allows the reservoir of energy
stored in the EnerChip to be delivered efficiently to the load when brief pulses of current are needed - for
example to power a wireless transmitter. Between transmissions, the EnerChip recharges the capacitor and
delivers steady state power to the load.
This Application Note provides detailed information on:
• Understanding the capacity and charge/discharge profile of the EnerChip thin film battery
• Determining the load pulse current requirements
• Calculating the optimal value for the external boost capacitor
EnerChip
Battery with
Internal
Impedance
Boost
Capacitor
Load with
Variable
Resistance
Figure 1. EnerChip with External Capacitor to Supplement Power to the Load.
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Doc AN-72-1025 Rev03
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