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LDO regulator with 0.3 µA current consumption and integrated battery voltage monitor

Ricoh Electronic Devices has launched the RP124, a 100mA LDO regulator with an integrated battery voltage monitor. According to Ricoh, this makes it possible to measure the remaining charge left in the battery.

The regulator features an ultra-low current consumption of only 0.3µA (at no-load), extending the lifetime of battery powered devices.

The additional battery monitor circuit is one of the key features of the RP124, a conventional way to measure the remaining battery charge is using an external resistor divider + MOSFET connected to an A/D Converter. However, the input impedance of this solution is typically low, resulting in a considerable current flow to ground, draining the battery and limiting the lifetime of the application.

The RP124 provides a solution via a built-in resistor divider and voltage follower as a buffer. This circuit has a much lower current flow to ground and the output is compatible with the input impedance of the A/D converter. In addition, all essential components for this circuit are integrated into the chip, reducing valuable circuit board space and cost.

There are a few product versions available with options for the CE pin and the automatic discharge function. The CE pin disables the LDO for the B and D-versions. As for the E-version, it has the possibility to disable the battery monitor circuit when not in use. It saves another 0.1µA, whilst the LDO remains in operation, resulting in a current consumption of only 0.2µA.

The RP124 (similar to the popular RP118 without battery voltage monitor) offers three operating modes:

1. Low power consumption mode, saving battery power at low output current demand

2. Fast transient response mode, enhanced dynamic performance at high output current demand

3. Off mode, to reduce current consumption to a minimum

The device switches automatically between the low power consumption and the fast transient response mode, based on the output current demand of the application. The performance of the LDO is enhanced in fast transient response mode. In particular, the ripple rejection as well as the response speed to line and load transients demonstrate better results compared to a conventional LDO with low current consumption, Ricoh adds. This means the RP124 contributes to optimised output voltage stability and ripple reduction. The Off Mode is controlled by the Chip Enable pin and turns the LDO offline, reducing current consumption to a minimum.

The RP124 features an embedded fold back current limit circuit. When a short circuit occurs at the output, this circuit will decrease the output current to a level of 65mA, protecting the LDO and other electronic parts of the application from possible damage. After removing the short, the regulator resumes to normal operation automatically.

Bethan Grylls

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