ADT7467ARQZ-R7 datasheet(15/77 Pages) ONSEMI

15 / 77 page

ADT7467

Rev. 3 | Page 15 of 77 | www.onsemi.com

ANALOG-TO-DIGITAL CONVERTER

All analog inputs are multiplexed into the on-chip, successive

approximation, analog-to-digital converter, which has a resolu-

tion of 10 bits. The basic input range is 0 V to 2.25 V, but the

input has built-in attenuators to allow measurement of VCCP

without any external components. To allow for the tolerance of

the supply voltage, the ADC produces an output of 3/4 full scale

(decimal 768 or 300 hexadecimal) for the nominal input voltage

and, therefore, has adequate headroom to deal with

overvoltages.

VOLTAGE MEASUREMENT INPUT

The ADT7467 has one external voltage measurement channel.

It can also measure its own supply voltage, VCC. Pin 14 can

measure VCCP. The VCC supply voltage measurement is carried

out through the VCC pin (Pin 3). Setting Bit 7 of Configuration

and be measured without overranging the VCC measurement

channel. The VCCP input can be used to monitor a chipset supply

voltage in computer systems.

Input Circuitry

The internal structure for the VCCP analog input is shown in

Figure 22. The input circuit consists of an input protection

diode, an attenuator, and a capacitor to form a first-order low-

pass filter that gives the input immunity to high frequency noise.

VCCP

17.5kΩ

52.5kΩ

35pF

Figure 22. Structure of Analog Inputs

Voltage Measurement Registers

VCCP Limit Registers

Associated with the VCCP and VCC measurement channels is a

high and low limit register. Exceeding the programmed high or

low limit causes the appropriate status bit to be set. Exceeding

either limit can also generate SMBALERT interrupts.

Table 6

shows the input ranges of the analog inputs and output

codes of the 10-bit ADC.

When the ADC is running, it samples and converts a voltage

input in 0.7 ms and averages 16 conversions to reduce noise; a

measurement takes nominally 11 ms.

ADDITIONAL ADC FUNCTIONS

FOR VOLTAGE MEASUREMENTS

A number of other functions are available on the ADT7467 to

offer the system designer increased flexibility.

Turn-Off Averaging

For each voltage measurement read from a value register,

16 readings are made internally, the results of which are averaged

and then placed into the value register. For instances where faster

conversions are needed, setting Bit 4 of Configuration Register 2

(0x73) turns averaging off. This produces a reading that is 16

times faster (0.7 ms), but the reading may be noisier.

Bypass Voltage Input Attenuator

Setting Bit 5 of Configuration Register 2 (0x73) removes the

attenuation circuitry from the VCCP input. This allows the user

to directly connect external sensors or to rescale the analog

voltage measurement inputs for other applications. The input

range of the ADC without the attenuators is 0 V to 2.25 V.

Single-Channel ADC Conversion

Setting Bit 6 of Configuration Register 2 (0x73) places the

ADT7467 into single-channel ADC conversion mode. In this

mode, the ADT7467 can be made to read a single voltage

channel only. If the internal ADT7467 clock is used, the selected

input is read every 0.7 ms. The appropriate ADC channel is

selected by writing to Bits <7:5> of the TACH1 minimum high

byte register (0x55).

Table 5. Programming Single-Channel ADC Mode

Bits <7:5>, Register 0x55

Channel Selected

001

VCCP

010

VCC

101

Remote 1 temperature

110

Local temperature

111

Remote 2 temperature

Configuration Register 2 (0x73)

<4> = 1, averaging off

<5> = 1, bypass input attenuators

<6> = 1, single-channel conversion mode

TACH1 Minimum High Byte (0x55)

<7:5> selects ADC channel for single-channel convert mode.

ADT7467ARQZ-R7 Datasheet(PDF) 15 Page - ON Semiconductor

ADT7467ARQZ-R7 Datasheet(HTML) 15 Page - ON Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77

Datasheet Download

Link URL