Rainbow Electronics MAX108 User Manual
Page 25
Thermal Performance
The MAX108 has been modeled to determine the ther-
mal resistance from junction to ambient. Table 7 lists
the ADC’s thermal performance parameters:
Ambient Temperature:
T
A
= +70°C
Heatsink Dimensions:
25mm x 25mm x 10mm
PC Board Size and Layout:
4 in. x 4 in.
2 Signal Layers
2 Power Layers
Heatsink Manufacturers
Aavid Engineering and IERC provide open-tooled, low-
profile heatsinks, fitting the 25mm x 25mm ESBGA
package.
Aavid Engineering, Inc.
Phone: 714-556-2665
Heatsink Catalog No.: 335224B00032
Heatsink Dimensions: 25mm x 25mm x 10mm
International Electronic Research Corporation (IERC)
Phone: 818-842-7277
Heatsink Catalog No.: BDN09-3CB/A01
Heatsink Dimensions: 23.1mm x 23.1mm x 9mm
Bypassing/Layout/Power Supply
Grounding and power-supply decoupling strongly influ-
ence the MAX108’s performance. At a 1.5GHz clock
frequency and 8-bit resolution, unwanted digital
crosstalk may couple through the input, reference,
power-supply, and ground connections and adversely
influence the dynamic performance of the ADC.
Therefore, closely follow the grounding and power-sup-
ply decoupling guidelines (Figure 22).
Maxim strongly recommends using a multilayer printed
circuit board (PCB) with separate ground and power-
supply planes. Since the MAX108 has separate analog
and digital ground connections (GNDA, GNDI, GNDR,
and GNDD, respectively), the PCB should feature sep-
arate analog and digital ground sections connected at
only one point (star ground at the power supply). Digital
signals should run above the digital ground plane, and
analog signals should run above the analog ground
plane. Keep digital signals far away from the sensitive
analog inputs, reference inputs, and clock inputs. High-
speed signals, including clocks, analog inputs, and
digital outputs, should be routed on 50
Ω
microstrip
lines, such as those employed on the MAX108 evalua-
tion kit.
The MAX108 has separate analog and digital power-
supply inputs: V
EE
(-5V analog and substrate supply)
and V
CC
I (+5V) to power the T/H amplifier, clock distri-
bution, bandgap reference, and reference amplifier;
V
CC
A (+5V) to supply the ADC’s comparator array;
V
CC
O (+3V to V
CC
D) to establish power for all PECL-
based circuit sections; and V
CC
D (+5V) to supply all
logic circuits of the data converter.
The MAX108 V
EE
supply contacts
must not
be left
open while the part is being powered up. To avoid this
condition, add a high-speed Schottky diode (such as a
Motorola 1N5817) between V
EE
and GNDI. This diode
prevents the device substrate from forward biasing,
which could cause latchup.
MAX108
±5V, 1.5Gsps, 8-Bit ADC with
On-Chip 2.2GHz Track/Hold Amplifier
______________________________________________________________________________________
25
Figure 21. MAX108 Thermal Performance
6
8
10
12
14
16
18
0
200
100
300 400 500 600 700 800
THERMAL RESISTANCE vs. AIRFLOW
AIRFLOW (linear ft./min.)
θ
JA
(°C/W)
WITHOUT
HEATSINK
WITH HEATSINK
Table 7. Thermal Performance for
MAX108 With or Without Heatsink
16.5
12.5
AIRFLOW
(linear ft/min)
0
MAX108
θ
JA
(°C/W)
14.3
9.4
200
13
8.3
400
12.5
7.4
800
WITHOUT
HEATSINK
WITH HEATSINK