PC87591L datasheet(171/437 Pages) NSC

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Embedded Controller Modules (Continued)

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Temperature Sensor Interface (TSI). The TSI generates the diode current and converts the voltage drop to a single-ended

voltage. In addition, the TSI of the remote diode enables open/short detection for the diode connection cable and sets the

corresponding status bits.

Analog Multiplexer. A 16 to 1 analog multiplexer selects one of the inputs for measurement by connecting it to the A/D con-

verter. Switching between inputs at different voltage levels requires delaying the conversion start until the input voltage to

the A/D converter has settled to the desired accuracy.

A/D Converter. The

Σ−∆, high-resolution A/D converter receives the selected input and converts it. The result of the con-

version is either a 10-bit, unsigned integer digital value (0 to 1023) for voltage inputs or an 8-bit, 2s complement digital value

(

−128 to +127) with the Least Significant Bit (LSB) having the value of 1°C for temperature inputs.

A high-precision internal reference generator sets the full-scale voltage value (VFS) of the A/D converter.

ADC Cycle. The ADC has four output “channels”: one for temperature and three for voltage measurement. The voltage

measurement channels are not related to specific inputs. They hold the input select control data for the next measurement

and contain a buffer in which the conversion result is stored. The temperature channel is slightly different, since it lacks the

input select control data. It “toggles” between the remote and local diode inputs, unless the remote diode input is disabled.

An ADC cycle includes measurements of all four channels and a calibration operation. The first measurement is of the tem-

perature channel, followed by a calibration measurement and the three voltage channels in ascending order, each for the

specific input number contained in its control register. The ADC waits for a programmable delay between the selection of an

input and the A/D conversion start that is necessary for A/D input settling to the required accuracy.

At the end of each A/D conversion, the result is stored in the corresponding buffer and a Data Valid (DATVAL) flag is set.

At the end of the ADC cycle, a flag is set indicating that all the channels contain new data. If enabled, an interrupt request

is sent to the core.

After reading the data at the end of the cycle, the software may choose to set up new values for the input select control data

in order to measure different inputs during the following cycle. Another option is to use the old values for one or more voltage

channels and repeat the measurement on the previous inputs for a higher sampling rate. Any voltage output channel may

be disabled in order to skip its related measurement during the ADC cycle (shorter cycle).

Digital Comparator. A digital comparator checks the temperature measured by the local diode by comparing it with a user-

programmable limit. When the temperature of the PC87591x exceeds the Overtemperature Limit, the Overtemperature

Shutdown (OTS) signal becomes active and an interrupt request (if enabled) is sent to the core.

ADC Control/Status Registers and Data Out Buffers. These may be read/written by the core through the Peripheral bus.

Timing Control. This block reduces the frequency of the system clock to the lower value required by the ADC.

PC87591L датащи(PDF) 171 Page - National Semiconductor (TI)