System Board 6660

MAXREFDES1151: Supercapacitor dv/dt Suppression Circuit


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Supercapacitors, by their very name, provide unique benefits in modern electronics. One critical application of supercapacitors is dv/dt suppression. In the dv/dt suppression application, a battery's internal resistance creates a voltage drop at the output of the battery when a load is connected, usually a heavy load. For example, when a 10A load is connected to a 10V battery with an internal resistance of 0.2Ω, the voltage drop is 2V. As the current increases, the battery output voltage decreases, called dv/dt. In order to avoid loss of voltage, designers can opt to design a very large battery into their system. Another more elegant choice is to use a supercapacitor for dv/dt suppression, where the supercapacitor provides additional energy, suppressing the load transient and preventing the battery voltage from collapsing. Such a design allows for a smaller battery, momentary heavy load conditions, and prolonged battery life.

This design includes two parts, the first part uses the MAX406 to charge the supercapacitors with 1A constant current; the second part uses the MAX1725 and MAX985 to realize dv/dt suppression.

The MAX406 is a single, low-voltage, micropower, precision op amp designed for battery-operated systems. It features a supply current of less than 1.2μA that is relatively constant over the entire supply range, which represents a 15 to 20 times improvement over industry-standard micropower op amps. A unique output stage enables this op amp to operate at ultra-low supply current while maintaining linearity under loaded conditions. In addition, the output is capable of sourcing 1.8mA when powered by a 9V battery.

Key Features

  • +2.5V to +10V Single-Supply Range
  • 500μV Max Offset Voltage (MAX406A)
  • < 0.1pA Typical Input-Bias Current
  • Output Swings Rail-to-Rail
  • Input Voltage Range Including Negative Remote
    Alarm Notification (RAI)
MAXREFDES1151 Hardware Enlarge+


This board is not available for purchase.

Designed, Built, Tested

This reference design describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to design the dv/dt suppression circuit. The circuit has been built and tested, details of which follow later in this document.

Design Resources

 
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MAX985
Micropower, Low-Voltage, UCSP/SC70, Rail-to-Rail I/O Comparators

  • 11µA Quiescent Supply Current
  • 2.5V to 5.5V Single-Supply Operation
  • Common-Mode Input Voltage Range Extends 250mV Beyond the Rails

MAX1725
12V, Ultra-Low-IQ, Low-Dropout Linear Regulators

  • 2µA Supply Current
  • Reverse-Battery Protection
  • +2.5V to +12V Input Voltage Range

MAX406
Single, Dual, Quad, 1.2µA Max, Single-Supply Op Amps

  • 1.2µA Max Quiescent Current per Amplifier
  • +2.5V to +10V Single-Supply Range
  • 500µV Max Offset Voltage (MAX406A/MAX409A)