Texas Instruments has introduced a 150mA linear regulator with 500nA tail current, and a dual level output.

"This is the lowest quiescent current of any regulator in the market that I am aware of," applications manager Michael Day told Electronics Weekly.

Made in 0.7µm linear BiCMOS, the first member of what will be the TPS780xx family is specifically aimed at further cutting the consumption of the firm's MSP430 low-power microcontroller in very long life battery applications.

Dual level output operation comes from a logic level input to the TPS780, which  switches its output from 3.3V to 2.2V.

"An MSP430 operating in standby or Low Power Mode 3 (LPM3) consumes 1.863µA with an input voltage of 3.3V," said Day. "Using the dynamic voltage scaling feature of the TPS780330220 to reduce the operating voltage to 2.2V while in LPM3 reduces the standby operating current by over 50 per cent to 0.9µA. This reduction in quiescent current becomes significant in applications such as remote wireless sensing where systems may operate in standby mode for greater than 99 per cent of the time."

The two output voltages are controlled through an internal EEPROM which can be factory set when more members of the family are required.

There is also an adjustable version, which requires an external pair of resistors to set its output. "We have been working with the sum of the two resistors at 2.7MΩ ," said Day - so around one additional microamp.

A novel feature in this regulator is an active pull-down on the output when it is disabled.

"A lot of people want a power supply to go off when it is turned off," said Day. "If they have significant capacitance, maybe several hundred microfarads, on the output they could get sequencing problems when the power is turned back on if that capacitance has not been discharged."

This feature only operates if input power is maintained. "The active pulldown works if you pull enable low with Vin applied," said Day. "If EN and Vin go down at the same time, the active pull down will not work."

Optimised for ultra-low quiescent operations from batteries, the device does have its limitations. "If you have extra large ripple on the input and require extra low ripple on the output, this is not the part for you. We have other parts for these applications," said Day.

External components are small, with the output only requiring 1µF for stable operation.
The devices come in a 6pin, 2x2mm, SON package.

TPS780xx at a glance

• 150mA regulator
• Pin-selectable dual voltage out
• Vout factory set across 0.8 - 5.0V
• Adjustable version
• 250mV typical drop out at 150mA
• 3% typical accuracy over load, line and temperature
• 500nA total quiescent current
• Thermal shutdown