MAX108 Maxim, MAX108 Datasheet - Page 24

• Manufacturer Part Number: MAX108
• Description: 5V / 1.5Gsps / 8-Bit ADC with On-Chip 2.2GHz Track/Hold Amplifier
• Manufacturer: Maxim

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
signal is speed control for a cooling fan to maintain
constant MAX108 die temperature. The circuit operates
by converting the I
ages V
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:
±5V, 1.5Gsps, 8-Bit ADC with
On-Chip 2.2GHz Track/Hold Amplifier
Figure 20. Die Temperature Acquisition Circuit with the MAX479
24
______________________________________________________________________________________
I
CONST
CONST
I
PTAT
6.65k
T
DIE
and V
A
A
V
V
300
CONST
PTAT
1
V
6.65k
CONST
1/4 MAX479
I
CONST
I
R
R
PTAT
, with appropriate scaling to
1
2
V
and I
TEMP
6.05k
2
R
R
V
PTAT
PTAT
1
3
273
currents to volt-
12.1k
12.1k
1/4 MAX479
2
JU1
1
3
V
PTAT
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
pins 1 and 2 on JU1 restores normal operation to the
circuit after the calibration is complete. The voltage at
the V
MAX108 die temperature according to the equation:
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.
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.
7.5k
R1
V
CONST
TEMP
node will then be proportional to the actual
3.32k
15k
R2
1/4 MAX479
T
TEMP
DIE
5k
(°C) = 100 V
15k
output is -2.728V. Connecting
R2
10-TURN
Thermal Management
7.5k
TEMP
R1
1/4 MAX479
V
TEMP