MAX17843ACB datasheet(30/131 Pages) MAXIM

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THRM Output

The THRM output has two modes of operation, automatic

and manual, as shown in Table 5.

The automatic mode minimizes power consumption, but

after the THRM output is enabled, the AUXIN voltages

must be allowed to settle before the conversion. Since the

auxiliary inputs are the last inputs measured, the duration

of the measurement cycle itself can provide sufficient set-

tling time, depending on what measurements are enabled

and the time constants for the auxiliary input circuit. Up

to 384μs of additional settling time, if required, can be

configured by ACQCFG[5:0] (see Table 6), or by utilizing

the manual mode. The ability to configure the settling time

allows for a range of time constants to be considered in

designing the auxiliary application circuit.

Computing Temperature

In Figure 9, VAUXINn = VTHRM x RTH/(10KΩ + RTH)

and this measurement is stored in the AINn register. The

thermistor resistance can then be solved for as follows:

RTH = (VAUX x 10kΩ)/(VTHRM - VAUXINn),

where VTHRM = 3.3V nominally.

The resistance of an NTC thermistor increases as the

temperature decreases and is typically specified by its

resistance R0 at T0 = 25°C = 298.15K and a material

constant β (3400K typ). To the first order, the resistance

RTH is at a temperature T in Kelvin can be computed as

follows:

R = R0e(β(1/T-1/T0))

The temperature T of the thermistor (in °C) can then be

calculated as follows:

T (in °C) = (β/ln((RTH/10kΩ) +

(β/298.15K)) - 273.15K

Temperature Alerts

Auxiliary voltage measurements can be directly compared

to precalculated voltages in the AINUT and AINOT reg-

isters that correspond to specific over/undertemperature

thresholds. When a measurement exceeds the AINUT

or AINOT threshold level, the ALRTCOLD or ALRTHOT

bits, respectively, are set in the STATUS register. An

alert is cleared only by a new measurement that is within

threshold.

Table 5. THRM Output

Table 6. AINTIME

MODE

ACQCFG[9:8]

DESCRIPTION

Automatic

00b

THRM output enabled at the beginning of the acquisition and disabled at the end

of the acquisition.

01b

Manual

10b

THRM output is enabled

11b

THRM output is disabled

ACQCFG[5:0] (AINTIME)

ADDITIONAL SETTLING TIME PER ENABLED AUXILIARY

CHANNEL = 6µs + (AINTIME x 6µs)

00h

6μs

01h

12μs

02h

18μs

…

1Fh

384 μs

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

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