MAX17823BGCV datasheet(21/121 Pages) MAXIM

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MAX17823B

12-Channel High-Voltage Data Acquisition System

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THRM Output

The THRM output has 2 modes of operation, automatic and manual as shown in Table 5.

Table 5. THRM Output

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

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 may provide sufficient settling 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] as shown in 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.

Table 6. AINTIME

ACQCFG[5:0]

(AINTIME)

Additional Settling Time per Enabled

Auxiliary Channel = 6µs + (AINTIME x 6µs)

00h

6μs

01h

12μs

02h

18μs

…

1Fh

384 μs

Computing Temperature

In Figure 6, 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 = (VTHRM 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 typical). To the first order, the resistance

RTH is at a temperature T in Kelvin may be computed as follows:

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 may be directly compared to pre-calculated voltages in the AINUT and AINOT

registers that correspond to specific over- and under-temperature 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.

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