Rainbow-electronics MAX104 Manual do Utilizador descarregar pdf (Página 24)

MAX104

of determining the die temperature is to measure each

current with an ammeter (which shuts off the internal

catch diodes) referenced to GNDI. The die temperature

in °C is then calculated by the expression:

Another method of determining the die temperature

uses the operational amplifier circuit shown in Figure 20.

The circuit produces a voltage that is proportional to

the die temperature. A possible application for this sig-

nal is speed control for a cooling fan, to maintain con-

stant MAX104 die temperature. The circuit operates by

converting the I

CONST

and I

PTAT

currents to voltages

CONST

and V

PTAT

, with appropriate scaling to account

for their equal values at +27°C. This voltage difference

is then amplified by two amplifiers in an instrumenta-

tion-amplifier configuration with adjustable gain. The

nominal value of the circuit gain is 4.5092V/V. The gain

of the instrumentation amplifier is given by the expres-

sion:

To calibrate the circuit, first connect pins 2-3 on JU1 to

zero the input of the PTAT path. With the MAX104 pow-

ered up, adjust potentiometer R3 until the voltage at the

TEMP

output is -2.728V. Connecting pins 1-2 on JU1

restores normal operation to the circuit after the calibra-

tion is complete. The voltage at the V

TEMP

node will

then be proportional to the actual MAX104 die tempera-

ture according to the equation:

DIE

(°C) = 100 · V

TEMP

The overall accuracy of the die temperature measure-

ment using the operational-amplifier scaling circuitry is

limited mainly by the accuracy and matching of the

resistors in the circuit.

Thermal Management

Depending on the application environment for the

ESBGA-packaged MAX104, the customer may have to

apply an external heatsink to the package after board

assembly. Existing open-tooled heatsinks are available

from standard heatsink suppliers (see

Heatsink

Manufacturers

). The heatsinks are available with pre-

applied adhesive for easy package mounting.

TEMP

CONST PTAT

−

=+ +

⋅1

DIE

PTAT

CONST













−⋅300 273

±5V, 1Gsps, 8-Bit ADC with

On-Chip 2.2GHz Track/Hold Amplifier

24 ______________________________________________________________________________________

CONST

TEMP

7.5k

15k

3.32k

7.5k

6.65k

6.05k

12.1k

JU1

10-TURN

PTAT

CONST

1/4 MAX479

Figure 20. Die Temperature Acquisition Circuit with the MAX479

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 30 31 32

±5V, 1Gsps, 8-Bit ADC with 1

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