MAX108 Datasheet, PDF (24/32 Pages) Maxim Integrated Products – ±5V, 1.5Gsps, 8-Bit ADC with On-Chip 2.2GHz Track/Hold Amplifier

±5V, 1.5Gsps, 8-Bit ADC with
On-Chip 2.2GHz Track/Hold Amplifier
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:
T_DIE
=
300
_ICI_POTNASTT



−
273
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
signal is speed control for a cooling fan to maintain
constant MAX108 die temperature. The circuit operates
by converting the I_CONST and I_PTAT currents to volt-
ages 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
instrumentation-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
expression:
A_V
=
V_TEMP
V_CONST − V_PTAT
A_V
=1+
R1
R2
+
2 ^R1
R3
To calibrate the circuit, first connect pins 2 and 3 on
JU1 to zero the input of the PTAT path. With the
MAX108 powered up, adjust potentiometer R3 until the
voltage at the V_TEMP output is -2.728V. Connecting
pins 1 and 2 on JU1 restores normal operation to the
circuit after the calibration is complete. The voltage at
the V_TEMP node will then be proportional to the actual
MAX108 die temperature 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 MAX108, 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 preap-
plied adhesive for easy package mounting.
I_PTAT
6.65k
I_CONST
6.65k
12.1k
1/4 MAX479
12.1k
R1
7.5k
JU1
1
2
3 ^VPTAT
3.32k
5k _10-TURN
R2
15k
R2
15k
R1
1/4 MAX479
7.5k
1/4 MAX479
6.05k
V_CONST
1/4 MAX479
V_TEMP
Figure 20. Die Temperature Acquisition Circuit with the MAX479
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