MAX17843 datasheet(46/131 Pages) MAXIM

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Oscillators

Two factory-trimmed oscillators provide all timing require-

ments: a 16MHz oscillator for the UART and control logic,

and a 32.768kHz oscillator for HV charge pump and tim-

ers. A special diagnostic counter clocked by the 16MHz

signal is employed to check the 32kHz oscillator. Every two

periods of the 32kHz clock, the counter is sampled. If the

count varies more than 5% from the expected value, the

ALRTOSC1 bit is set, as shown in Table 19. A redundant

alert bit (ALRTOSC2) increases the integrity level. If the

16MHz oscillator varies by more than 5%, communication

errors are indicated.

Device ID Number

The ID1[15:0] register, together with ID2[7:0], contain a

24-bit manufacturing identification number (DEVID[23:0]).

The ID, combined with the manufacturing date, provides

a means of uniquely identifying each device. A device ID

of zero is invalid.

Power-On And Shutdown

Applications that remain connected continuously to the

power source rely on the SHDNL input to shut down and

reset the device. When VSHDNL < 0.6V, the regulator is

disabled, the POR signal asserted, and the device goes

into an ultra-low-power-shutdown mode. When VSHDNL

> 1.8V, POR is deasserted, the regulator is enabled, and

the device becomes fully operational in the standby mode.

Power-On Method

The SHNDL input can be driven externally, or can be

controlled using UART communication only. In differential

mode, the signaling on the lower-port receiver drives an

internal charge pump that charges up the external 1nF

capacitor connected to the SHDNL input (see Figure 23).

VSHDNL reaches 1.8V in 200μs (typ). The charge pump

then self-regulates to VSHDNLIMIT and can maintain

VSHDNL at a logic-one even with the UART in idle 98%

of the time.

Table 19. Oscillator Diagnostics

Figure 23. SHDNL Charge Pump

FAULT

CONDITION

ALERT BIT

LOCATION

32.768kHz oscillator

31.129kHz > fosc_32k > 34.406kHz

ALRTOSC1

FMEA115

32.768kHz oscillator

31.129kHz > fosc_32k > 34.406kHz

ALRTOSC2

FMEA114

16MHz oscillator

15MHz > fosc_32k > 17MHz

ALRTMAN or ALRTPAR

STATUS4, or STATUS2

C42

2nF 600V

C43

2nF 600V

C40

15pF

C41

15pF

R40

4.7kΩ

R42

100kΩ

R43

100KΩ

R41

4.7kΩ

FROM DEVICE (n-1)

TRANSMITTER

CIRCUIT

C44

1nF

(CSHDNL)

DCIN

10MΩ

FORCEPOR

TO RECEIVER

RXLP

RXLN

GNDL

SHDNL

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

www.maximintegrated.com

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