External RPD circuitry examples

AN2691

8/10

The value of the resistor R, instead, is linked to the time needed to charge the capacitor C.

Normally 220 k

Ω < R < 1 MΩ

.

2.2

Alternate configuration

If both synchronous reset and interruptible power down modes are not required, it is

possible to connect the RPD pin to ground, directly or through a resistance.

Figure 5.

RPD pin connected to ground

The internal pull-up is sized to allow a direct connection to ground without any problem to

the internal circuitry.

As already explained, with this kind of connection, any pulse longer than 500 ns on the

RSTIN pin leads to an asynchronous reset. Moreover, it is not advised to use an interruptible

power-down.

Table 2.

RSTIN pulse length and reset events in the presence of an RC network

Pulse length

Event

No effect (filtered)

Short synchronous reset

Long synchronous reset

Asynchronous reset

RPD

Pull-Up

Weak Pull-Down

(~ 200

µA)

driven by internal

reset/pwrnd

circuitry