Single-Cell AA/AAA, 555-Like Analog Timer with Battery-Safe Operation

Dec 21, 2010 6:19 PM

Semtech Corp. announced a sub-1 V analog timer platform that revolutionizes the conventional 555 timer for low-voltage, battery-operated small appliances. The new SX8122 analog timer offers the best-in-class battery life via its intrinsic 0.9 V operation, without the need for an external boost converter and inductor, saving board space and cost. It also adds low-voltage features to the legacy 555 timer, with one output that controls a DC motor or another continuous low-voltage element and another output that generates a pulse train to drive a high-brightness LED from a single battery. This combination of features makes the SX8122 ideal for a wide range of small consumer home and office appliances, such as electric toothbrushes, buzzers, toys, and LED pointers. The device also includes a voltage monitor to enable a simple USB charger for NiMH or NiCd supplied devices.

The new Semtech SX8122 timer operates between 0.9 V and 2 V over the full industrial temperature range of -40 to +85°C, making it ideally suited to run from one AA or AAA alkaline, NiMH or NiCd battery. The device has a continuous output that can be activated on the press of a button to control either a DC motor or other continuous low voltage function, as well as a burst output to drive a high-brightness white or green LED, or other feature requiring a voltage boost. The SX8122 timer is programmable via external resistors and a capacitor, similar to the legacy 555 analog timer but at 1 V, and is designed for on/off button debouncing, delayed start-up functions, and analog programmable sequencing and time-out in toys and remote control applications.

The SX8122 is battery safe. It starts controlling I/Os at 0.6 V, to eliminate unexpected behavior in the external components and prevent current drain during the start-up phase. It also features a battery overload indicator for slow NiMH or NiCd charger management. At power down (low battery), the I/Os are controlled again down to 0.6 V and the current consumption is guaranteed less than 10 µA over the full industrial temperature range to avoid battery leakage.

The SX8122 is the only single-chip, application-specific solution that operates intrinsically from 0.9 V, while managing the battery and providing precise timing. By directly providing DC and burst outputs, it can drive continuous loads, as well as loads with high threshold voltage.

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