Single-supply μP monitoring circuit monitors bipolar power supply

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description:

The circuit shown in Figure 1 monitors the bipolar supply in accordance with user-defined positive and negative reset thresholds. The circuit generates a reset signal when either voltage is below (usually falling to 0V) the corresponding threshold. IC2 can generate both a low-level reset and a high-level reset.

The positive voltage is monitored by the comparator inside IC2 and the 1.7V reference, plus the R1/R2 divider; the negative voltage is monitored by the internal power-up failure comparator, which provides the signal from the R3/R4 divider. The same 1.7V reference source is compared for implementation. The positive voltage required to supply this voltage divider is greater than 1.7V and is provided by the 2.5V reference source IC1, independent of Vcc. Vcc varies from 3V to 5.5V.

This connection method has the opposite action as the normal connection method: when the negative voltage fails, PF0 (pin5) is high level, not low level. This change pulls the manual reset (MR) to low by transistor Q1. Level, generating a power failure signal triggers a reset output.

In order to set the reset threshold voltage, first select R2 and R4. It should be noted that if the resistance is too low, power consumption will be wasted; when the resistance is too high, the error will occur due to the leakage current of the comparator; R1 and R3.

Among them, Vp is the positive voltage reset threshold.

Here VN is the negative voltage reset threshold.

The reset threshold can be set to any level greater than ±1.7V. If a precision reset threshold is required, the voltage divider should have a resistance accuracy greater than ±1%.