AMC7823 datasheet(27/48 Pages) TI

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ON-CHIP TEMPERATURE SENSOR

SW2

SW1

I (10 A)

I (750 A)

Diode Temperature

Sensor

ADC

CH8 (TEMP)

AMC7823

SLAS453A – APRIL 2005 – REVISED OCTOBER 2005

The AMC7823 has an integrated temperature sensor to measure the on-chip temperature. This measurement

relies on the characteristics of a semiconductor p-n junction operating at a known current level. The forward

voltage of the diode (VBE) depends on the current passing through it and the junction temperature.

Channel CH8 is dedicated to the on-chip temperature sensor. When CH8 is converted, the on-chip temperature

measurement process is activated. Two measurements, and therefore two ADC conversions, are required to

capture the temperature data. First, the diode is driven by current I1 (750 µA) and the forward voltage VBE1 is

measured. Next, the diode is driven by current I2 (10 µA) and VBE2 is measured. The difference of these two

voltages,

∆V

BE, is stored in the ADC-8 Data Register as straight binary code. See Figure 46.

NOTE: When CH8 is converted, two conversions are performed. During the first conversion, SW1 is turned on, SW2 is off,

and the diode is driven by I1 (750 µA). During the second conversion, SW2 is turned on, SW1 is off, and the diode is

driven by I2 (10 µA).

Figure 46. Local Temperature Sensor Operation

In direct-mode operation, the temperature can be measured by converting Channel CH8 only, or by converting

several channels including Channel CH8. In auto-mode, the temperature must be measured by converting at

least two channels including Channel CH8.

The following equations illustrate the corresponding temperature calculation process:

∆V

BE (mV) = decimal code (convert from ADC-8 Data Register binary code) × 1.22 mV for VREF = 2.5 V

∆V

BE (mV) = decimal code (convert from ADC-8 Data Register binary code) × 0.61 mV for VREF = 1.25 V.

Temp (°K) = 2.6 ×

∆V

BE (mV)

Temp (°C) = 2.6 ×

∆V

BE (mV) – 273°K.

The resolution of this calculation is 3.2°C/LSB when the reference voltage is 2.5 V and 1.6°C/LSB for a reference

voltage of 1.25 V.

AMC7823 Datasheet(PDF) 27 Page - Texas Instruments

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