DFE252012P-2R2M datasheet(26/44 Pages) MICROCHIP

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MCP16501

DS20006388A-page 26

 2020 Microchip Technology Inc.

is terminated and the MCP16501D waits for 100 ms.

After this wait time, a new start-up sequence is gener-

ated in the attempt to restart the system correctly.

A special feature is provided to enable system recovery

if there is a restart sequence after a Fault occurs while

in Hibernate mode. In Hibernate mode, the PWRHLD

had been previously set to low by the MPU and the

MPU expects a wake-up event in order to set PWRHLD

to high again. This must be a hardware event, which is

flagged to some I/O inside the MPU Shutdown and

Wake-up Controller (SHDWC) block (e.g., a logic

transition on a WKUPx or PIOBUx pin).

However, if a Fault causes a restart sequence while in

Hibernate mode, the restart sequence is not success-

fully completed until a wake-up event is generated for

the MPU SHDWC, because the PWRHLD remains low.

It is necessary for the PWRHLD signal to be high just

prior to the completion of the start-up sequence so that

nRSTO can be deasserted.

This is solved by generating from the MCP16501 an

Automatic Wake-up Pulse (AWKP) on the nSTRTO

output if the Fault that generates a restart sequence

has occurred while in Hibernate mode.

In the MCP16501D, the AWKP function is enabled by

default.

The timing diagram of a restart sequence caused by a

Fault while in Hibernate mode is shown in Figure 4-10.

Just before initiating the restart sequence, the

MCP16501D generates a 25 ms (nominal duration)

Automatic Wake-up Pulse on the nSTRTO output, even

in lack of a low level on the nSTRT input. This is the

only situation where the nSTRTO logic level does not

reflect the nSTRT input status. The duration of the

AWK Pulse erodes into the 100 ms waiting time that

precedes the automatic restart sequence.

PWRHLD will typically return high as soon as the

nSTRTO signal is detected to be low by the MPU

SHDWC. If LPM stays high for any reason, the

MCP16501D will go in Low-Power mode immediately

after the automatic start-up sequence. This behavior is

shown in Figure 2-21 in Section 2.0 “Typical Perfor-

mance Curves”.

If the restart sequence after a Fault is executed in any

other operational state but Hibernate, PWRHLD will

either be already high (in applications with backup

power) or it would return high as soon as the VDDIO rail

is started, thus making the generation of the Automatic

Wake-up Pulse not necessary.

FIGURE 4-10:

Automatic Wake-Up Pulse

Generation Timing Diagram (Fault during

Hibernate).

VIN

Fault

Event

PWRHLD

Wait 100 ms

(internal logic signal)

nSTRTO

nRSTO

time

LPM

Hibernate

Automatic Start-up Sequence

State

nSTRT

25 ms

100 ms

Wait after Fault

ACTIVE

75 ms

restart

Where:

trestart = Duration of the automatic start-up

(restart) sequence

t5 = Minimum setup/hold time: Min. 0 µs

(internal filtering applies)

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