Supercapacitor dV/dt Suppression Circuit Reference Design

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.

The MAXREFDES1151 reference design from Maxim Integrated Products 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 include:

• +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)