ADP5041ACPZ-1-R7 datasheet(29/40 Pages) AD

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Data Sheet

ADP5041

Rev. B | Page 29 of 40

RSTO

nRSTO

VOUT2

VTH

tRP

tRD

Figure 104. Reset Timing Diagram

The ADP5041 has a reset threshold programming input pin,

VTHR, to monitor a supply rail.

The reset threshold voltage at VTHR input is typically 0.5 V.

To monitor a voltage greater than 0.5 V, connect a resistor

divider network to the device as shown in Figure 105, where

















MONITORED

VREF = 0.5V

VTHR

MONITORED VOLTAGE

Figure 105. External Reset Threshold Programming

Do not allow the VTHR input to float or to be grounded.

Connect it to a supply voltage greater than its specified

threshold voltage. A small capacitor can be added on VTHR to

improve the noise rejection and to prevent false reset

generation.

The ADP5041 can be factory programmed to a 2.25 V or 3.6 V

UVLO threshold. When monitoring the input supply voltage, if

the selected reset threshold is below the UVLO level, the reset

output, nRSTO, is asserted low as soon as the input voltage falls

below the UVLO threshold. Below the UVLO threshold, the

reset output is maintained low down to ~1 V input voltage. This

is to ensure that the reset output is not released when there is

sufficient voltage on the rail supplying a processor to restart the

processor operations.

Manual Reset Input

The ADP5041 features a manual reset input (MR) which, when

driven low, asserts the reset output. When MR transitions from

low to high, the reset remains asserted for the duration of the

reset active timeout period before deasserting. The MR input

has a 52 kΩ, internal pull-up connected to AVIN, so that the

input is always high when unconnected. An external push-

button switch can be connected between MR and ground so

that the user can generate a reset. Debounce circuitry for this

purpose is integrated on chip. Noise immunity is provided on the

MR input, and fast negative-going transients of up to 100 ns

(typical) are ignored. A 0.1 μF capacitor between MR and ground

provides additional noise immunity.

Watchdog Input

The ADP5041 features a watchdog timer that monitors

microprocessor activity. The watchdog timer circuit is cleared

with every low-to-high or high-to-low logic transition on the

watchdog input pin (WDI), which detects pulses as short as 80 ns.

If the timer counts through the preset watchdog timeout period

(tWDI), an output reset is asserted. The microprocessor is required

to toggle the WDI pin to avoid being reset. Failure of the

microprocessor to toggle WDI within the timeout period,

therefore, indicates a code execution error, and the reset pulse

generated restarts the microprocessor in a known state.

As well as logic transitions on WDI, the watchdog timer is also

cleared by a reset assertion due to an undervoltage condition on

the monitored rail. When reset is asserted, the watchdog timer

is cleared and does not begin counting again until reset deasserts.

The watchdog timer can be disabled by leaving WDI floating or

by three-stating the WDI driver.

The ADP5041 can be factory programmed to two possible

watchdog timer values as indicated in Table 18.

WDI

tRP

tWD

tRP

VTH

VSENSED

nRSTO

Figure 106. Watchdog Timing Diagram

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