Rainbow Electronics MAX104 - Manual (Page 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
V 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
V
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:
T 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.
A
V
V V
A
R
R
R
R
V
TEMP
CONST PTAT
V
=
−
= + +
⋅
1
1
2
2
1
3
T
I
I
DIE
PTAT
CONST
=





 −
⋅
300 273
±5V, 1Gsps, 8-Bit ADC with
On-Chip 2.2GHz Track/Hold Amplifier
24 ______________________________________________________________________________________
V
CONST
V TEMP
R1
7.5k
R2
15k
R2
15k
3.32k 5k
R1
7.5k
6.65k
6.65k
6.05k
12.1k
12.1k
1
2
3
JU1
10-TURN
I
PTAT
V
PTAT
I
CONST
1/4 MAX479
1/4 MAX479
1/4 MAX479
1/4 MAX479
Figure 20. Die Temperature Acquisition Circuit with the MAX479