S-5840BAG-M5T1X Datasheet, PDF (8/15 Pages) Seiko Instruments Inc – TEMPERATURE SWITCH IC

TEMPERATURE SWITCH IC (THERMOSTAT IC) WITH LATCH
S-5840B Series
Rev.2.1_01
 Operation
1. Basic operation
The S-5840B Series is a temperature switch IC (thermostat 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.
Following is about the operation when the DET pin output logic is active "H".
When the power supply voltage is turned on, the DET pin voltage goes to "L" 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 "L" 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 "H". Once the over-temperature is detected and the DET pin goes to "H", 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 (VR − VHYS) 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 S-5840B Series.
2. Noise suppression circuit
The noise suppression circuit prevents malfunction of the temperature switch caused by noise.
The noise suppression 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 "L" since the charging of
the external capacitor (CD) is insufficient. As a result, the DET pin is held "L" and malfunction does not occur.
Noise suppression time (tnoise) is determined by the time constant consisting of internal constant current and the
capacitance of the CD, and calculated by the following equation.
tnoise (ms) = Noise suppression time coefficient × CD (nF)
Noise suppression time coefficient (Ta = +25°C): 6.4 typ.
The CD 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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