G767F datasheet(5/14 Pages) GMT

5 / 14 page

Ver: 2.5

Dec 14, 2004

TEL: 886-3-5788833

http://www.gmt.com.tw

G767

Global Mixed-mode Technology Inc.

Figure 1. Functional Diagram

A/D Conversion Sequence

If a Start command is written (or generated automati-

cally in the free-running auto-convert mode), both

channels are converted, and the results of both meas-

urements are available after the end of conversion. A

BUSY status bit in the status byte shows that the de-

vice is actually performing a new conversion; however,

even if the ADC is busy, the results of the previous

conversion are always available.

Remote-Diode Selection

Temperature

accuracy

depends

having

good-quality, diode-connected small-signal transistor.

Accuracy has been experimentally verified for all of the

devices listed in Table 1. The G767 can also directly

measure the die temperature of CPUs and other inte-

grated circuits having on-board temperature-sensing

diodes.

The transistor must be a small-signal type with a rela-

tively high forward voltage; otherwise, the A/D input

voltage range can be violated. The forward voltage

must be greater than 0.25V at 10µA; check to ensure

this is true at the highest expected temperature. The

forward voltage must be less than 0.95V at 100µA;

check to ensure this is true at the lowest expected

temperature. Large power transistors don’t work at all.

Also, ensure that the base resistance is less than

100

Ω. Tight specifications for forward-current gain

(+50 to +150, for example) indicate that the manufac-

turer has good process controls and that the devices

have consistent VBE characteristics.

Thermal Mass and Self-Heating

Thermal mass can seriously degrade the G767’s ef-

fective accuracy. The thermal time constant of the

SSOP-16 package is about 140sec in still air. For the

G767 junction temperature to settle to within +1°C

after a sudden +100°C change requires about five

time constants or 12 minutes. The use of smaller

packages for remote sensors, such as SOT23s, im-

proves the situation. Take care to account for thermal

gradients between the heat source and the sensor,

and ensure that stray air currents across the sensor

package do not interfere with measurement accuracy.

DXP

DXN

MUX

REMOTE

LOCAL

ADC

CONTROL

LOGIC

STBY ADD0 ADD1

ADDRESS

DECODER

SMBUS

SMBDATA

SMBCLK

READ WRITE

DIODE

FAULT

COMMAND BYTE

(INDEX) REGISTER

STATUS BYTE

CONFIGURATION

BYTE REGISTER

CONVERSION RATE

ALERT RESPONSE

ADDRESS REGISTER

LOCAL EMPERATURE

DATA REGISTER

HIGH-TEMPETATURE

THRESHOLD (LOCALT

HIGH)

LOW-TEMPETATURE

THRESHOLD (LOCAL T

LOW)

DIGITAL COMPARATOR

(LOCAL)

SELECTED VIA

SLAVE ADD = 0001 100

ALERT

REMOTE TEMPERATURE

DATA REGISTER

HIGH-TEMPETATURE

THRESHOLD (REMOTE

HIGH)

LOW-TEMPETATURE

THRESHOLD (REMOTE

LOW)

DIGITAL COMPARATOR

(REMOTE)

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