ADT7468 查看數據表（PDF） - ON Semiconductor

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ADT7468

dBCool® Remote Thermal Controller and Voltage Monitor

ON Semiconductor 

ADT7468

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

inputs have built-in attenuators to allow measurement of 2.5 V,

3.3 V, 5 V, 12 V, and the processor core voltage VCCP without any

external components. To allow for the tolerance of these supply

voltages, the ADC produces an output of 3/4 full scale (decimal

768 or 300 hex) for the nominal input voltage and therefore has

adequate headroom to cope with overvoltages.

VOLTAGE MEASUREMENT INPUT

The ADT7468 has four external voltage measurement channels

and can measure its own supply voltage, VCC. Pins 20 to 23 can

measure 5 V, 12 V, 2.5 V supplies, and the processor core voltage

VCCP (0 V to 3 V input). The VCC supply voltage measurement is

carried out through the VCC pin (Pin 4). Setting Bit 7 of Config-

uration Register 1 (Reg. 0x40) allows a 5 V supply to power the

ADT7468 and be measured without overranging the VCC

measurement channel. The 2.5 V input can be used to monitor a

chipset supply voltage in computer systems.

Input Circuitry

The internal structure for the analog inputs 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 input immunity to high frequency noise.

12VIN

120kΩ

20kΩ

30pF

5VIN

93kΩ

47kΩ

30pF

3.3VIN

68kΩ

71kΩ

30pF MUX

2.5VIN

45kΩ

94kΩ

30pF

VCCP

17.5kΩ

52.5kΩ

35pF

Figure 22. Structure of Analog Inputs

Voltage Measurement Registers

Reg. 0x20, 2.5 V reading = 0x00 default

Reg. 0x21, VCCP reading = 0x00 default

Reg. 0x22, VCC reading = 0x00 default

Reg. 0x23, 5 V reading = 0x00 default

Reg. 0x24, 12 V reading = 0x00 default

Voltage Limit Registers

Associated with each voltage measurement channel 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.

Reg. 0x44, 2.5 V low limit = 0x00 default

Reg. 0x45, 2.5 V high limit = 0xFF default

Reg. 0x46, VCCP low limit = 0x00 default

Reg. 0x47, VCCP high limit = 0xFF default

Reg. 0x48, VCC low limit = 0x00 default

Reg. 0x49, VCC high limit = 0xFF default

Reg. 0x4A, 5 V low limit = 0x00 default

Reg. 0x4B, 5 V high limit = 0xFF default

Reg. 0x4C, 12 V Low Limit = 0x00 default

Reg. 0x4D, 12 V High Limit = 0xFF default

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 ADT7468 to

offer the system designer increased flexibility.

Turn-Off Averaging

For each voltage measurement read from a value register,

16 readings have actually been made internally and the results

averaged before being placed into the value register. For

instance, where faster conversions are needed, setting Bit 4 of

Configuration Register 2 (Reg. 0x73) turns averaging off. This

effectively gives a reading 16 times faster (0.7 ms), but the

reading may be noisier.

Bypass Voltage Input Attenuator

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

the attenuation circuitry from the 2.5 V, VCCP, VCC, 5 V, and 12 V

inputs, which allows the user to directly connect external

sensors or 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.

Rev. 3 | Page 16 of 81 | www.onsemi.com

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