SH3100IMTR datasheet(9/80 Pages) SEMTECH

9 / 80 page

SH3100

POWER MANAGEMENT

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The main power supply is between VDD and GND and may

have any value between 1.7V and 5.5V for normal opera-

tion. In order to guarantee start-up, VDD should initially be

taken to at least 100mV above the reset threshold (VBO)

in order to overcome the reset threshold hysteresis; e.g.,

for a VBO level of 2.8V, VDD must initially rise to at least

2.9V for the chip to come out of reset.

The battery backup supply is between VBAK and GND. The

SH3100 switches to VBAK, if VDD drops below VBO and

VBAK is within its valid operating range of 0.9V to 5.5V for

battery backup.

While VBAK is within its valid operating range during bat-

tery backup, RTC operation is maintained and those reg-

ister contents not reset by a VBO reset event (Brownout)

are maintained. Any functions not required during battery

backup are shut down to save power.

Note: If the 32.768kHz system clock output is enabled on

CLK1 during battery backup then the maximum VBAK voltage

for valid CLK1 output is 4.5V. Battery backup continues for

VBAK voltages above 4.5V, but the CLK1 output is no longer

guaranteed to function correctly.

Power Supplies & Battery Backup

When running in battery backup from the 32.768kHz

crystal oscillator, full RTC accuracy is maintained down to

the minimum VBAK of 0.9V.

When running in battery backup from the internal

32.768kHz oscillator, RTC accuracy is maintained only

down to a VBAK level of 1.7V. Below this point, operation

continues down to 0.9V, but a ﬂag is set to indicate that

the internal oscillator can no longer be guaranteed to be

within ±3% of 32.768kHz.

The minimum VBAK level is guaranteed as 0.9V; however,

depending on process variations, operation may continue

down to 0.7V before battery back up fails.

An unpowered (cold) chip starts up and initializes only

when VDD is applied. Applying only VBAK to a cold chip

does not cause it to start up.

Battery backup facility is only enabled once the chip has

come out of reset after an initial power-up.

SH3100IMTR Datasheet(PDF) 9 Page - Semtech Corporation

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