BA45F5xxx Smoke Detector Integrated Analog Front End Application Notes
AN0540EN V1.00 1 / 5 March 9, 2020
BA45F5xxx Smoke Detector Integrated
Analog Front End Application Notes
D/N: AN0540EN
Introduction
The BA45F5xxx series of MCUs include an integrated analog front end (AFE) for use by smoke
detectors, allowing designers to develop related products with a minimum of external components.
This application note introduces the principles and application description of this kind of AFE.
Functional Description
The following figure shows a block diagram of an independent type smoke detection alarm product.
When smoke enters the product, the smoke detection circuit will generate a tiny current signal. The
AFE is responsible for this current signal, converting it to a voltage signal and amplifying it, and
then determining whether an alarm threshold has been reached using an A/D. After this, the product
will generate an alarm output signal. This application note explains the AFE part in the figure below.
Smoke Detector
Circuit
AFE
A/D sampling and
alarm output
Note: 1. In the smoke detection products, the photoelectric smoke detector commonly
uses optical refraction and has a labyrinth cavity.
2. Optical refraction is composed of infrared receiving and transmitting transistors.
3. The labyrinth cavity is designed to minimise any noise detected by the infrared
receiver when no smoke is present.
4. When smoke enters the labyrinth cavity, the infrared radiation will be diffused,
which will then be detected by the receiving part.