MAX17843 datasheet(48/131 Pages) MAXIM

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Shutdown Mode

Shutdown is performed by bringing VSHDNL < 0.6V.

Table 20 summarizes the methods by which this can be

achieved.

The quickest shutdown can be achieved by driving

SHDNL externally with a driver pulldown impedance not

exceeding 1kΩ. If SHDNL is not driven externally, the

host can discharge CSHDNL under software control by

setting the FORCEPOR bit. This will enable a pulldown

(4.7kΩ nominal) to discharge the capacitor with a 4.7μs

time constant.

The slowest method is for the host to simply cease

communication. With the UART idle, there is no charge

pumping and the capacitor discharges through an internal

10MΩ resistor, with a 10ms time constant. If shutdown

faster than 10ms is desired when power is disconnected

from the device, a 200kΩ resistor can be connected

externally from SHDNL to AGND to create a 200μs time

constant.

If only a reset is required, the host can issue a soft-reset

by setting the SPOR bit. This resets the device registers

and disables high-voltage operation, but low-voltage

operation remains enabled (the regulator is not disabled).

Note: For single-ended communication, SHDNL must

be driven externally since the charge-pump operation

requires a differential signal.

Shutdown Sequence

The shutdown sequence and timing is shown in Figure 25,

Figure 26, and Figure 27. The ALRTSHDNL status bit is

set and the low-voltage regulator disabled as soon as

VSHNDL < 0.6V. When the VAA and VDDL decoupling

capacitors discharge below the POR threshold (2.95V

typ), the device registers are reset and the HV charge

pump disabled. The device is then in an ultra-low-power

state until VSHDNL > 1.8V.

Figure 25. Shutdown Sequence

Table 20. Shutdown Timing

SHUTDOWN METHOD

RPULLDOWN

CSHDNL

1. Host drives SHDNL pin low

1kΩ

External

1nF

1µs

2. Host sets FORCEPOR bit

5kΩ

Internal

5µs

3. Disconnect DCIN

200kΩ

External

200µs

4. Host places UART in idle mode

10MΩ

Internal

10,000µs

POR ACTIVE

VAA > VPOR_RISING

POR INACTIVE

CHECK VAA

VAA < VPOR_FALLING

OSCILLATOR, CHARGE

PUMP, DIGITAL LOGIC

DISABLED

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

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