S-5840B Datasheet, PDF (6/13 Pages) Seiko Instruments Inc – TEMPERATURE SWITCH IC WITH LATCH

TEMPERATURE SWITCH IC WITH LATCH
S-5840B Series
Rev.1.2_00
„ Operation
Basic operation
The S-5840B Series is a temperature switch IC which detects the temperature and sends a signal to an external device.
The users can select a combination of the parameters such as detection temperature and release voltage.
The following explains the case when DET output is assumed to be active high.
When the power supply voltage is turned on, the DET pin voltage goes to low since the flip-flop circuit in the detection
circuit is cleared by the voltage detection circuit. Temperature detection then starts and the DET pin is held low as long
as the temperature is lower than the detection temperature. When the temperature rises and when the temperature
exceeds the detection temperature; longer than the time defined by the capacitor connected to the CD pin, the DET pin
goes to high. Once the over-temperature is detected and the DET pin goes to high, the state is held by the flip-flop
circuit. In order to release the state, the power supply voltage should be set under the detection voltage (V_R − V_HYS) of
the built-in voltage detector circuit to reset the internal circuit.
Using the internal reference voltage and built-in temperature sensor, a detection temperature accuracy of ±2.5°C is
achieved in the IC.
[Noise filtering circuit]
The noise filtering circuit prevents malfunction of the temperature switch caused by noise.
The noise filtering circuit starts charging the capacitor connected to the CD pin when the output of the internal
comparator enters the active state due to an external noise or a rapid change in the power supply voltage. In the
normal operation, the flip-flop circuit is set when the capacitor is charged to a certain voltage. But in the noise
triggered operation, the comparator output goes back to the inactive state and the CD pin voltage is held low since the
charging of the capacitor is insufficient. As a result, the DET pin is held low and malfunction does not occur.
Noise filtering time (t_noise) is determined by the time constant consisting of internal constant current and the
capacitance (C_D), and calculated by the following equation.
t_noise (ms) = Noise filtering time coefficient × C_D (nF)
Noise filtering time coefficient (25°C) : Typ. 6.4
Capacitance of the external capacitor C_D has no limitation as long as its leak current is negligible compared to the
internal constant current. The difference occurs in delay time if the capacitor has a leak current.
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Seiko Instruments Inc.