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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

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