Description

STM1831

6/24

Doc ID 18180 Rev 1

1.1

Pin descriptions

See Figure 1 and Table 1 for a brief overview of the signals available on this device.

Power supply (VCC)

This pin is used to provide power to the device. A 0.1 µF decoupling ceramic capacitor is

recommended to be connected between the VCC and VSS pins, as close to the STM1831

device as possible.

Sense voltage input (VSEN)

Input voltage on this pin is monitored. When it drops below the threshold (VDET), reset

output (RST) is asserted. If VCC is close to 0 V, internal logic disconnects the voltage divider

from VSEN input in order to minimize ISEN current (see Figure 3 and Figure 20).

Reset output (RST)

Reset output is asserted when the voltage on the VSEN input pin drops below the threshold

(VDET).

The STM1831 has an open drain, active-low output which sinks current when the output is

asserted. Connect a pull-up resistor from RST to any supply voltage up to 6 V (see

Figure 4). Select a resistor value large enough to register a logic low, and small enough to

register a logic high, while all of the input current and leakage paths connected to the reset

output line are being supplied. A 10 k

Ω pull-up is sufficient in most applications.

The advantages of open drain output include the ability to connect more open drain outputs

in parallel (wired OR connections) as well as connecting the output to a power supply

voltage other than VCC.

Delay capacitor (CD)

Capacitor CD determines the delay (tCD) between reset deassertion and the moment when

VSEN voltage exceeds the VDET threshold (see Figure 5 with calculations for more details).

Any external leakage due to poor quality timing capacitors or excessive humidity may cause

a significant leakage current which extends the tCD timing. To minimize this effect, the PCB

tracks between the CD pin and its respective timing capacitor should be as short as

possible, properly covered with solder mask and isolated from other tracks (especially VSS)

by as great a distance as possible. Low-leakage timing capacitors (ceramic or film capacitor)

should be used.

Leave CD pin open if unused (i.e. tCD = 0 ms).