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2019-2020 Microchip Technology Inc.

Preliminary

DS20006168B-page 9

47L64

FIGURE 3-3:

AUTOSTORE/AUTORECALL SCENARIOS (WITH ARRAY NOT MODIFIED)

3.2.4

TRIP VOLTAGE

The 47L64 has an internal voltage reference that is

used to create a trip voltage threshold (VTRIP). When

VCAP rises above VTRIP, a power-up event is detected.

If this is the first power-up event after a POR, then an

AutoRecall operation is initiated. When VCAP falls

below VTRIP, a power-down event is detected and an

AutoStore operation is initiated if the array has been

modified.

3.2.5

POWER SWITCHOVER

To support the AutoStore feature, the 47L64 must be

able to charge the capacitor connected to the VCAP pin

when power is available on VCC, and also

automatically switch to being powered from the VCAP

pin when power is removed from VCC. Since the VCAP

pin is used as part of the internal power bus, this

means that VCC must be disconnected when power is

removed.

To accomplish this, the 47L64 has an intelligent power

switchover circuit that continuously monitors the

voltages on both VCC and VCAP.

During a power-up event, VCC is initially disconnected,

allowing it to rise above VCAP. Once VCC is above

VCAP, VCAP is connected to the VCC, charging the

external capacitor. When VCAP reaches VTRIP, the

AutoRecall operation is triggered.

During a power-down event, VCC is initially connected

to the internal power bus. As Vcc falls, it discharges

the external cap, causing VCAP to also fall. Once VCAP

falls below VTRIP, the AutoStore operation is triggered,

and VCC is disconnected to prevent discharging the

capacitor further through VCC.

VTRIP

VCAP

VTRIP

VCAP

AutoStore

AutoRecall

Device Access

Enabled

Array Modified

AutoStore

AutoRecall

Device Access

Enabled

Array Modified

TRESTORE

VCC

CHARGE_CAP(1)

VCC

CHARGE_CAP(1)

Note 1: When CHARGE_CAP is a ‘0’, VCC is connected to VCAP, allowing VCC to charge the external capacitor. See

Section 3.2.5 “Power Switchover” for details.

VPOR

VPOR

Note:

When VCAP is below VTRIP, the 47L64

cannot be accessed and will not

acknowledge any commands.