AN1475: High Temperature Behavior of ISL3178AE

High Temperature Behavior of ISL3178AE
®
Application Note
July 7, 2009
Description
set to provide a burst mode of five pulses at a bit rate of
10Mbps.The RX device was wired up with two
thermocouples one placed on the device case top and the
the other placed on the PWB near the GND pin. The RX
device was heated using a temperature forcing system from
+25°C to +200°C. The Rx showed one threshold point.
The ISL3178AE is a 3.3V based RS-485 MIL temperature
rated transceiver aimed at addressing applications that
require high operating temperatures. The receiver inputs A
and B are presented in pins 6 and 7; when RE is low, this
differential input signal is processed and available at the RO
pin. The Driver input is presented at pin 4 and the driver
differential outputs Z and Y are available at pins 6 and 7
respectively when DE is high. This Application Note aims at
characterizing the device at temperatures from +125°C to
+200°C.
At a Data rate of 10Mbps:
1. The pulse width 70% threshold is at a die temp of
min. = +190°C and max. = +196°C while operating at a
data rate of 10Mbps.
This is based on a sample size of 15pcs. and a six sigma
distribution.
Device Pinout
TX High Temperature Test
ISL3178AE
(8 LD SOIC)
TOP VIEW
RO 1
R
RE 2
DE 3
DI 4
D
AN1475.0
8
VCC
7
B/Z
6
A/Y
5
GND
The TX was tested using a the EVALB TX portion of
Figure 2. The 200ft cable was disconnected and
terminations of 100Ω and 54Ω were connected based on
test requirement. The parameters tested were: Driver
differential output voltage, propagation delay, and skew. The
results are per the “Typical Performance Curves” on page 2.
Supply Current vs High Temperature
The supply current is found to have a knee at around
+195°C, and increases rapidly thereafter. The supply current
with (driver enabled) DE high is typically around 517µA. This
value increases to about 1143.5µA at +240°C. With DE
connected to GND (driver disabled) the supply current drops
to about 400µA typical. The value of supply current
increases from a temperature of +200°C and higher to about
605.6µA.
Figure 1 shows the evaluation board schematic. The device
evaluation board is common to TX and RX. The mode of
operation is determined by the logic presented to the DE and
RE pins.
RX High Temperature Test
Figure 2 shows the High temperature test setup. The board
wired up as the transmitter is called the EVALB TX and the
one wired the receiver is called the EVALB RX. The
differential lines were hooked up through 200ft. of twisted
pair cable terminated on either side by 120Ω. The VIN was
set to a worst case of 4.5V. The driver input of the EVALB TX
is connected to a function generator capable of providing
fast rise and fall times. The function generator output was
Driver Input vs High Temperature
The Driver input did not latchup at a VIN = 3.0V up to
+220°C. This is likely because the device VIN is below the
holdoff.
VCC/3.3V/PIN8
C6
10u
TP3/RO/PIN1
0
U1
TP4/RE#/PIN2
1
2
3
4
TP5/DE/PIN3
TP6/DI/PIN4
RO
RE
DE
DI
VCC
TX-Z / RX-B
TX-Y / RX-A
GND
8
7
6
5
ISL3178
C2B
0.1u
0
TP8/TX-Z/RX-B/PIN7
R10
120
TP7/TX-Y/RX-A/PIN6
GND/PIN5
R5
49.9
0
R6
49.9
0
R7
49.9
0
FIGURE 1. EVALUATION BOARD SCHEMATIC
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Application Note 1475
SCOPE1/CH3
SCOPE1/CH1
SCOPE1/CH4
SCOPE1/CH2
CABLE 200ft
V2
3V
V3
3V
VCC/3.3V/PIN8
0
TP4/RE#/PIN2
TP5/DE/PIN3
RX
0
TP4/RE#/PIN2
TP8/TX-Z/RX-B/PIN7
TP5/DE/PIN3
VCC/3.3V/PIN8
TX
TP7/TX-Y/RX-A/PIN6
TP7/TX-Y/RX-A/PIN6
TP6/DI/PIN4
EVALB
V1 = 0
V2 = 3
TD = 0
TR = 1ns
TF = 1ns
PW = 100ns
PER = 200ns
TP3/RO/PIN1
SCOPE1/CHx
GND/PIN5
TP3/RO/PIN1
GND/PIN5
TP6/DI/PIN4
TP8/TX-Z/RX-B/PIN7
EVALB
V1
0
0
0
SCOPE1/CHx
FIGURE 2. HIGH TEMPERATURE SETUP
2.9
2.7
2.5
RDIFF = 100Ω
2.3
2.1
1.9
RDIFF = 54Ω
1.7
-55
0
55
110
165
1.5
220
DIFFERENTIAL OUTPUT VOLTAGE (V)
Typical Performance Curves
TEMPERATURE (°C)
FIGURE 3. TPLH AND TPHL AT A DIE TEMPERATURE OF
+231°C
2
FIGURE 4. DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs
TEMPERATURE
AN1475.0
July 7, 2009
Application Note 1475
Typical Performance Curves (Continued)
60
50
ICC DE-VCC
45
ICC (µA)
55
40
ICC DE-GND
-55
FIGURE 5. COMPRESSED TIMESCALE TO SHOW RINGING
AT THE RX INPUT AT +202°C
0
55
11
TEMPERATURE (°C)
165
FIGURE 6. SUPPLY CURRENT vs TEMPERATURE
45
35
30
25
tPLH
20
15
10
5
-55
0
55
110
165
0
220
TEMPERATURE (°C)
FIGURE 7. DRIVER DIFFERENTIAL PROPAGATION DELAY
vs TEMPERATURE
FIGURE 9. TX/RX WAVEFORM AT +194.2°C TYP, 10Mbps
AND VIN = 3.0V
1.5
1.4
1.3
1.2
SKEW (ns)
tPHL
1.6
PROPOGATION DELAY (ns)
40
35
22
SKEW
1.1
-55
0
55
110
165
1.0
22
TEMPERATURE (°C)
FIGURE 8. DRIVER DIFFERENTIAL SKEW vs TEMPERATURE
FIGURE 10. TX/RX WAVEFORM AT +194.2°C TYP, 10Mbps
AND VIN = 3.0V
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verify that the Application Note or Technical Brief is current before proceeding.
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3
AN1475.0
July 7, 2009
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