Intersil ISL3331EVAL1Z User manual

1
®
AN1471.0
ISL3331EVAL1Z User’s Manual
Description
The ISL3331EVAL1Z evaluation board is RoHS compliant,
and provides a quick and easy method for evaluating this
Dual Protocol IC. The evaluation board also accommodates
the ISL3333; see the “ISL3333EVAL1Z User’s Manual” for
details.
This board was designed to allow the user to evaluate all the
features available on the ISL3330 and ISL3331 products.
The ISL3331 is the full featured version (see “Key Features”
in next section), where the QFN package’s increased pin
count gives the user access to functionality not available on
the pin limited ISL3330. The same die is used in both
products, so other than minor package effects, evaluating
the QFN packaged ISL3331 is a reasonable substitute for
evaluating the ISL3330.
By changing jumper positions the user can quickly set the
board to evaluate any of the ISL3331’s many modes and
features, and the input states can also be set via jumpers.
Refer to the ISL3331 data sheet for complete details
regarding the functions and features of this device. These
dual protocol ICs feature many modes, so studying the
device’s truth-table along with its operating circuits and
detailed description is the best way to gain an understanding
of how the part works.
Key Features
• QFN Version Demonstrates All Enhanced Features:
- Logic Supply Pin (VL)
- Three RS-485 Speed Options -
115kbps/460kbps/20Mbps
- Active Low RS-485 Rx Enable for Simple Direction
Control
• Quick Configuration Using Jumpers
• State of All Inputs Can be Set by Jumper Positions
• No Bus Termination Resistors; Allows RS-232 or RS-485
Evaluation
• Simple Operation Requires Only One, 3.3V, Power Supply
Important Notes
To facilitate locating jumpers on this board, Figure 3 is a
jumper locator and, in this Application Note, the (#) following
a jumper mention corresponds to the red jumper number on
the locator. See the “Jumper Definitions” section for a
description of the function of each jumper.
The base board is used to evaluate both the ISL3333
(2-port) and ISL3331 (1-port) products, so the jumper and
connector names reflect the functionality of both products.
Due to space limitations some jumper labels are
abbreviated, but the corresponding BNC connector has the
full label.
In most cases, a name that applies to both products contains
no parenthesis (e.g., “B1”), a name that applies to only the
ISL3333 is followed by “(NC)” (e.g., “B2 (NC)”), and a name
that applies to only the ISL3331 is preceded by “NC” and/or
has the name in parenthesis (e.g., “NC (RXEN)” or
“(RXEN)”).
It is important to note that the ISL333x don’t follow the
RS-485 convention whereby the inverting I/O is labeled
“B/Z”, and the noninverting I/O is “A/Y”. Thus, the ISL3330
and ISL3331 A/Y (B/Z) pins connect to the B/Z (A/Y) pins of
generic RS-485/422 ICs.
Input signals that are likely to be driven by a generator
connect to a BNC connector, and there is a 50Ωtermination
resistor to GND when the jumper is in the “LOW” position.
Default Configuration
As delivered (see “Functional Diagram (Default
Configuration)” on page 2), the evaluation board is
configured for powered-up (not SHDN) RS-485 mode, driver
enabled, via DEN, and set for high speed (20Mbps)
operation, driver input (DY) low, Rx enabled via the RXEN
line, Rx inputs floating, and VLshorted to VCC. To achieve
this configuration, the jumpers are installed as follows
(unlisted jumpers are not installed, and (#) indicates the
jumper number on the Figure 3 jumper locator):
A2 (485/232)(7) =VH;(DEN)(8) =VH;SPB(9) =VH;
RXEN1 (10) =VH;(RXEN)(11) = VH; (ON) (12) =VH;
DY1(DZ/SLEW) (13) = VH; DZ1/DE1(DY) (14) =LOW;
RXBIAS-VCC (15) = installed; VCC-VL(16) = installed;
VL-VHIGH (17) = installed.
Note that there are no differential termination resistors on
either the Rx inputs nor the Tx outputs. If these resistors are
desired, they can be added at positions R9and R7,
respectively.
Application Note June 4, 2009
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 |Intersil (and design) is a registered trademark of Intersil Americas Inc.
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All other trademarks mentioned are the property of their respective owners.

2AN1471.0
June 4, 2009
Functional Diagram (Default Configuration)
Supply Banana Jacks
There are eight banana jacks at the top of the board for
power supply connections, but only VCC and GND are
required connections. The function and use of each jack
(from left to right) are:
VLOAD - This is a load voltage driving the load resistors
connected to the Rx and Tx outputs (Tx resistors - R5and
R6- not populated); used mostly during output enable and
disable time characterizations.
GND - Common connection for any supplies used.
RXBIAS - A voltage that can be applied to any or all Rx
inputs via jumpers “J9” and “J10” (3 and 2); the
“RXBIAS-VCC” (15) jumper shorts this jack to VCC, so
remove this jumper if supplying a voltage other than VCC.
V+ - Used to monitor the positive charge pump voltage in
RS-232 mode.
V- - Used to monitor the negative charge pump voltage in
RS-232 mode.
VCC - The 3.3V supply connection.
VHIGH - Connects to all the “VH” positions on the jumpers to
define the high level voltage for logic and Tx inputs; the
“VL-VHIGH” (17) jumper shorts this jack to VL, so remove
this jumper if supplying a voltage other than VL.
VL - The logic supply voltage that sets the ISL3331’s Rx
output VOH levels, and the logic and Tx input switching
points; the “VCC-VL” (16) jumper shorts this jack to VCC, so
remove this jumper if supplying a voltage other than VCC.
Getting Started
Connect a 3.3V, 500mA minimum, power supply to the VCC
and GND banana jacks. It is recommended that an ammeter
be used between the supply and the board, so that ICC can
be monitored. Ensure that the “RXBIAS-VCC” (15),
“VCC-VL” (16) and “VL-VHIGH” (17) jumpers are installed in
the upper right hand corner of the board.
External Loopback Via Jumpers
To evaluate the Rx and Tx performance at the same time, an
external loopback can be implemented simply by installing
jumpers “A1/Y1_LB (5) and “B1/Z1_LB (6). In this
configuration, the Tx output lines connect to the
corresponding Rx input lines, so the data driven on the Tx
input(s) appears at the Rx output(s). In RS-485 mode, data
driven on DY loops back through A and B to RA. In RS-232
mode, DY loops back to RA, and DZ loops back to RB.
For RS-485 mode, installing resistors R7and R9allows
evaluation of performance with the Tx driving a double
terminated load.
Basic RS-485 DC Evaluation
GENERAL OBSERVATIONS
ICC should be approximately 1.2mA.
Measure V+ and V- at the banana jacks - V+ = VCC and
V- = GND, indicating that the charge pumps are off for low
power and low noise.
RAis high - due to the “full failsafe” Rx - while RBis always
tri-stated because it is unused in RS-485 mode.
Note that this evaluation board isn’t populated with
differential termination resistors on either the Rx inputs nor
the Tx outputs. If these resistors are desired, they can be
added at positions R9and R7, respectively.
RECEIVER TESTS
The “full failsafe” nature of the Rx can be evaluated by
manipulating the “A1” (1) and “B1” (4) input jumpers. In the
default configuration, A1 and B1 float, but RA (measure at
the “RB1(RA)” test point to the right of jumper (1)) remains
high due to the failsafe “open” functionality. Installing
jumpers “A1” (1) and “B1” (4) effectively shorts the two inputs
together (i.e., VID =0).R
Astill remains high, indicating that
the Rx is also failsafe “shorted”. The combination of failsafe
“open” and “shorted” yields a “full-failsafe” Rx.
To switch the Rx output state leave the “B1” (4) jumper
installed, remove the “A1” (1) jumper, and install the A1 Rx
bias jumper, “J10” (2). The “RXBIAS-VCC” (15) jumper now
drives the A1 input voltage to VCC, which switches RA low.
Removing the “RXBIAS-VCC” (15) jumper, and connecting a
power supply between the “RXBIAS” banana jack and GND
34
VCC
Y1
Z1
DY
SLEW
0.1µF
+0.1µF
+
0.1µF
28
27
4
5
37
38 1
19
V+
V-
C1+
C1-
C2+
C2-
+
0.1µF
36
35
RA
A1 2
RB
B1 329
C1
C2
+C3
C4
RXEN 20
GND
+3.3V +0.1µF
15, 16
485/232 ON
11 21 VH
VH
DEN
12
VH
30
D
R
VH
31
VL
SPB VH
VH
14
RXEN 17 VH
VHIGH (VH)
(17)(16)
Application Note 1471

3AN1471.0
June 4, 2009
now sets the Rx differential input voltage, via “A1”, and
varying this supply switches the Rx output state. For
example, with the RXBIAS supply = 0V (VID =0V)the
output is high, and increasing RXBIAS to at least +200mV
(VID = -200mV) switches RA low.
To disable the Rx output via the active high RXEN pin,
ensure that the “RXEN1” (10) jumper is in the “VH” position,
and move jumper “(RXEN)” (11) to the “LOW” position. To
disable the Rx output via the active low RXEN pin, ensure
that the “(RXEN)” jumper is in the “LOW” position, and move
jumper “RXEN1” to the “VH” position.
Return the “RXEN1” and “(RXEN)” jumpers to the “VH”
position, remove the “RXBIAS” power supply and jumpers
“J10” and “B1”, and reinstall the “RXBIAS-VCC” jumper.
DRIVER TESTS
Tx DC output levels are independent of Tx speed setting. In
the default configuration, the driver input, DY, is low, so the
Tx noninverting output, Z1, is low, while the inverting output,
Y1, is high. To switch the output states, simply move the
“DZ1/DE1 (DY) (14) jumper to the “VH” position. In either
state, note the good differential voltage (VOD) of ≈2.9V. To
evaluate the double terminated VOD (≈2.0V), install resistors
R7and R9, and configure the evaluation board for “external
loopback”, as described previously (i.e., install jumpers (5)
and (6)).
To disable the Tx output via the active high DEN pin, move
the “(DEN)” (8) jumper from the “VH” to the “LOW” position.
When finished, return the “DZ1/DE1 (DY)” and “(DEN)”
jumpers to the “LOW” and “VH” positions respectively, and
remove the “external loopback” jumpers.
INTERNAL LOOPBACK
To configure the ISL3331 for internal loopback mode, simply
move the “(ON)” (12) jumper to the “LOW” position, while
ensuring that the “(DEN)” (8) and “(RXEN)” (11) jumpers are
set to “VH”. Note that ICC increases by ≈1.3mA, due to the
enabling of the loopback receivers. RA is now low due to the
Tx outputs internally driving the Rx. You can repeat the
previous Rx switching tests to confirm that the external Rx
input pins now have no affect on RA.
The internal loopback receivers are not RS-485/422
compliant, so internal loopback can’t be used to create a
half duplex transceiver.
LOW POWER SHDN
With the “(ON)” (12) jumper still in the “LOW” position, move
the “(DEN)” (8) and “(RXEN)” (11) jumpers to the “LOW”
position, while ensuring that the “RXEN1” (10) jumper is set
to “VH”. This setting places the ISL3331 into shutdown
(SHDN), which disables the Tx and Rx outputs, and places
the IC in its lowest power mode. Note that ICC drops to
10µA.
Return jumpers “(ON)”, “(DEN)”, and “(RXEN)” to the “VH”
position.
Basic RS-485 AC Evaluation
Remember that there aren’t any differential term resistors,
so if they are desired they must be added at positions R7-
for the Tx - and R9for the Rx.
RECEIVER TESTS
Before starting, ensure that the jumpers are back in the
default positions. Note that the RS-485 Rx operates at high
speed, regardless of the Tx speed selection.
Add jumper “B1” (4) to connect that input to GND, and add
jumper “A1” (1) to engage the 50Ωterm. Connect a
generator to the “A1” BNC, and set it for a -1.5V to +1.5V
swing. Monitoring test points “TP6” (input), and “RB1 (RA)”
(output) with a scope allows the Rx prop delays and skews
to be measured. If desired, you can load the Rx output with a
1kΩresistor by adding jumper “J6” (not numbered), located
below test point “RB1 (RA)”. This resistor terminates to the
“VLOAD” banana jack (upper left hand corner), allowing the
resistor to be terminated to GND by shorting “VLOAD” to
GND, or terminated to any voltage by connecting “VLOAD”
to an external supply.
You can also measure the Rx enable/disable time to/from a
low output state via the active high RXEN pin. From the
previous jumper configuration, leave the “B1” and “J6”
jumpers installed, remove the “A1” jumper, and install the A1
Rx bias jumper, “J10” (2). Connect the “VLOAD” jack to VCC,
switch the “(RXEN)” (11) jumper to the low position to
engage the 50Ωterm, set the generator to swing from 0V to
3V, and move the generator to the “DEN2 (RXEN)” BNC.
Monitoring test points “TP12” (input), and “RB1 (RA)”
(output) with a scope allows the Rx enable and disable times
to be measured. To evaluate the Rx enable/disable time
to/from a high output state, simply remove “J10”, and
connect “VLOAD” to GND.
To evaluate the Rx enable/disable times using the active low
RXEN pin, repeat the previous test but leave the “(RXEN)”
jumper in the “LOW” position, move the “RXEN1” (10)
jumper to the “LOW” position to connect the 50Ωterm, and
connect the generator to the “RXEN1” BNC.
TX SPEED SELECTION
Before performing any Tx switching tests, ensure that the
jumpers are in their default positions, and then configure the
“DZ/(SLEW)” (13) and “SPB” (9) jumpers for the desired Tx
speed setting. Table 1 details the jumper settings for each of
the speed options.
TABLE 1. JUMPER SETTINGS FOR Tx SPEED SELECTION
DATA RATE J-(DZ/SLEW) (13) J-SPB (9)
115kbps “LOW” “LOW”
460kbps “LOW” “VH”
20Mbps “VH” “LOW” or “VH”
Application Note 1471

4AN1471.0
June 4, 2009
DRIVER TESTS
There are no driver loads on this board, so if loading is
desired a differential load resistor, and/or differential load
capacitor may be added at position “R7”. Alternatively, single
ended loads (Y or Z to GND) may be added at positions “C4”
and “C2”.
Ensure that the “DZ1/DE1 (DY)” (14) jumper is in the “LOW”
position to engage the 50Ωterm resistor, connect the
generator to the “DZ1/DE1 (DY)” BNC, and set the swing for
0V to 3V. Monitoring test points “TP18” (input), and “TP5”
and “TP2” (Y and Z outputs respectively) with a scope allows
the Tx prop delays, skews, and transition times to be
measured. To view the differential waveform, use the
scope’s math function to generate “Z-Y”.
To measure the Tx output enable and disable times, start
with the previous jumper configuration and move the
“DEN” (8) jumper to the “LOW” position to engage its 50Ω
term resistor. Connect the generator to the “DEN1 (DEN)”
BNC, and set the swing for 0V to 3V. Monitoring test points
“TP9” (input), and “TP5” and “TP2” (Y and Z outputs
respectively) with a scope allows the enable and disable
times to be measured. Note that some form of termination
resistor must be used to pull the disabled outputs to a known
state; a differential termination resistor at “R7” is the easiest
approach.
EVALUATING DRIVER AND RECEIVER COMBINED
PERFORMANCE
Performance through a cascaded Tx and Rx can easily be
evaluated, utilizing the external loopback function, by
installing jumpers “A1/Y1_LB (5) and “B1/Z1_LB (6). In this
configuration, the Tx output lines connect to the
corresponding Rx input lines, so the data driven on the Tx
input (DY) appears at the Rx output (RA).
Installing resistors R7and R9allows evaluation of the
performance with the Tx driving a double terminated load.
Interconnecting Driver and Receiver with a Cable
To evaluate the performance of the Tx and Rx
interconnected by a cable, start with the default
configuration, connect single wire of a twisted pair between
test points “TP2” and “TP1”, and connect the other wire in
the pair between “TP5” and “TP6”. Ensure that the
“DZ1/DE1 (DY)” (14) jumper is in the “LOW” position to
engage the 50Ωterm resistor, connect the generator to the
“DZ1/DE1 (DY)” BNC, and set the swing for 0V to 3V.
Monitoring test points “TP18” (input), and test point
“RB1(RA)” illustrates the overall input to output performance.
Installing resistors R7and R9allows evaluation of the
performance with the Tx driving a double terminated cable.
Switching to RS-232 Mode
To set the board for RS-232 evaluation, start with the
jumpers in the “default configuration”, and move jumper
“A2 (485/232)” (7) to the “LOW” position. If RS-485
termination resistors (“R7” or “R9”) were added, ensure that
they have been removed. Note that the RS-232 data rate is
fixed at 400kbps, so the “SPB” (9) jumper has no affect
(connect it high to minimize SHDN ICC), and that the
“SLEW” pin becomes the second driver input, DZ. Figure 1
illustrates the ISL3331 configuration in this mode.
Basic RS-232 DC Evaluation
GENERAL OBSERVATIONS
Note that V+ and V- now pump up to approximately +6V and
-5.6V, respectively, and the charge pump operation
increases ICC to 3.9mA. Also note that RS-232 drivers and
receivers are inverting by definition.
Before starting, ensure that resistors R7and R9are
removed, if they have been previously installed.
RECEIVER TESTS
In the default configuration of Figure 1, RB (measure at the
“RA1 (RB)” test point to the left of jumper (14)) and RA
(measure at the “RB1(RA)” test point to the right of
jumper (1)) are high due to the A1 and B1 5kΩinput
resistors to GND.
To switch the Rx output states, install the A1 and B1 Rx bias
jumpers, “J10” (2) and “J9” (3). The “RXBIAS-VCC” (15)
jumper now drives the Rx input voltages to VCC, which
switches RA and RB low. Removing the “RXBIAS-VCC”
jumper and connecting a power supply between the
“RXBIAS” banana jack and GND, allows this supply to set
Y1
Z1
DY
DZ
0.1µF
+0.1µF
+
0.1µF
28
27
4
5
37
38 1
19
V+
V-
C1+
C1-
C2+
C2-
+
0.1µF
36
35
RA A1 2
5kΩ
RB B1 329
5kΩ
C1
C2
+C3
C4
RXEN
17
GND
+3.3V +0.1µF
15, 16
485/232 ON
11 21 VH
VH
DEN
12
VH
30
R
R
D
D
34
VCC
31
VL
RXEN
20 VH
FIGURE 1. DEFAULT RS-232 CONFIGURATION
VHIGH (VH)
(17)(16)
VH
Application Note 1471

5AN1471.0
June 4, 2009
the Rx input voltages, in case the user wants to evaluate the
Rx switching points.
To disable the Rx outputs via the active high RXEN pin,
remove “J10” (2) and “J9” (3), and switch the “(RXEN)” (11)
jumper to the “LOW” position (make sure the “RXEN1” (10)
jumper is in the “VH” position). To disable the Rx outputs via
the active low RXEN1 pin, move jumper “RXEN1” to the
“VH” position (make sure the “(RXEN)” jumper is in the
“LOW” position).
Return the “RXEN1” and “(RXEN)” jumpers to the “VH”
position, remove the “RXBIAS” power supply, and reinstall
the “RXBIAS-VCC” (15) jumper.
DRIVER TESTS
The RS-232 Tx outputs, Y and Z, are high (≈6.2V) and low
(≈-5.7V), respectively, in the default configuration. To switch
the output states, simply switch the “DY1 (DZ/SLEW)” (13)
and “DZ1/DE1 (DY)” (14) jumpers to the opposite states. To
evaluate the loaded driver output voltages, configure the port
for “external loopback”, as described previously (i.e., install
jumpers (5) and (6)). Each driver output is now loaded by an
Rx input resistor (≈5kΩ), and the output voltages still exceed
±5.5V.
The driver outputs can be disabled by moving the
“(DEN)” (8) jumper to the “LOW” position.
Remove the “external loopback” jumpers when finished,
switch the “DY1(DZ/SLEW)” and “(DEN)” jumpers to the
“VH” position, and move the “DZ1/DE1 (DY)” jumper back to
the “LOW” position.
INTERNAL LOOPBACK
To configure the ISL3331 for internal loopback mode, simply
move the “(ON)” (12) jumper to the “LOW” position, while
ensuring that the “(DEN)” (8) and “(RXEN)” (11) jumpers are
set to “VH”. Note that ICC increases due to the enabling of
the loopback receivers. RA is now low due to Tx output Y
feeding back to Rx A, while RB is high due to Z feeding back
to Rx B. You can repeat the previous Rx switching tests to
confirm that the external Rx input pins now have no affect on
RA nor RB.
LOW POWER SHDN
The ISL3331 enters the SHDN mode when
“(ON)” (12) = “LOW”, and the Tx and Rx are disabled
(“(DEN)” (8) = “LOW”, “(RXEN)” (11) = “LOW”, and
“RXEN1 (10) = “VH”), and the already low supply current
drops to as low as 10µA. SHDN disables the Tx and Rx
outputs, and disables the charge pumps, so V+ collapses to
VCC, and V- collapses to GND.
All but 10µA of SHDN ICC current is due to the on-chip SPB
pull-up resistor (~10µA/resistor), so SHDN ICC varies
depending on the ISL333x configuration. To evaluate the
lowest SHDN ICC, ensure that the “SPB” (9) jumper is in the
“VH” position.
SINGLE TX AND SINGLE TRANSCEIVER MODES
RS-232 mode also offers the options of selecting a single Tx
mode, or a single Tx/Rx pair mode. To evaluate the single Tx
mode, set the “(ON)” (12) and “(RXEN)” (11) jumpers “LOW”
and “(DEN)” (8) and “RXEN1” (10) jumpers to “VH”. To
evaluate the single Tx/Rx mode, set the “(ON)” and “(DEN)”
jumpers “LOW” and either the “RXEN1” jumper to “LOW” or
the “(RXEN)” jumper to “VH”.
Basic AC Evaluation
Before starting, ensure that the jumpers are back in the
default RS-232 positions. Note that the RS-232 data rate is
fixed, so the speed select pins have no effect.
RECEIVER TESTS
Add jumper “A1” (1) to engage the 50Ωterm, connect a
generator to the “A1” BNC, and set it for at least a 0V to 3V
swing. Monitoring test points “TP6” (input), and “RB1(RA)”
(output) with a scope allows the Rx prop delays and skews
to be measured. If desired, you can load the Rx output with a
1kΩresistor by adding jumper “J6” (not numbered), located
below test point “RB1 (RA)”. This resistor terminates to the
“VLOAD” banana jack (upper left hand corner), allowing the
resistor to be terminated to GND by shorting “VLOAD” to
GND, or terminated to any voltage by connecting “VLOAD”
to an external supply.
To measure the Rx enable/disable time to/from a high output
state via the active high RXEN pin, start from the previous
jumper configuration, leave the “J6” jumper installed, and
connect the “VLOAD” banana jack to GND. Remove the “A1”
jumper (Rx input is pulled low by its on-chip pull-down),
switch the “(RXEN)” (11) jumper to the low position to
engage the 50Ωterm, set the generator to swing from 0V to
3V, and move the generator to the “DEN2 (RXEN)” BNC.
Monitoring test points “TP12” (input), and “RB1 (RA)”
(output) with a scope allows the Rx enable and disable times
to be measured. To evaluate the Rx enable/disable time
to/from a low output state, install the A1 Rx bias jumper,
“J10” (2).
To evaluate the Rx enable/disable times using the active low
RXEN pin, repeat the previous test but leave the “(RXEN)”
jumper in the “LOW” position, move the “RXEN1” (10)
jumper to the “LOW” position to connect the 50Ωterm, and
connect the generator to the “RXEN1” BNC.
DRIVER TESTS
Ensure that the “DZ1/DE1 (DY)” (14) jumper is in the “LOW”
position to engage the 50Ωterm resistor, connect the
generator to the “DZ1/DE1 (DY)” BNC, and set the swing for
0V to 3V. Monitoring test points “TP18” (input) and “TP5”
(output) with a scope, allows the Tx prop delays, skews, and
transition times to be measured.
To measure the “loaded” driver performance, simply remove
the “J10” (2) jumper, and connect the “A1/Y1_LB” (5) jumper,
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June 4, 2009
which connects an Rx input, including its 5kΩpull-down, to
the driver output.
To measure the Tx output enable/disable times to/from a
high output state, start with the previous jumper
configuration and move the “(DEN)” (8) jumper to the “LOW”
position to engage its 50Ωterm resistor. Connect the
generator to the “DEN1 (DEN)” BNC, and set the swing for
0V to 3V. Monitoring test points “TP9” (input), and “TP5”
(output) with a scope allows the enable and disable times to
be measured. Note that some form of output termination
resistor must be used to pull the disabled output to a known
state; installing the “A1/Y1_LB” jumper is the easiest
solution.
EVALUATING DRIVER AND RECEIVER COMBINED
PERFORMANCE
Performance through a cascaded Tx and Rx can easily be
evaluated, utilizing the external loopback function. Ensure
that the “A1/Y1_LB (5) jumper is installed, that the
“(DEN)” (8) and “(RXEN)” (11) jumpers are set to the “VH”
position, and that the “DZ1/DE1(DY)” (14) jumper is in the
“LOW” position. Connect the generator to the
“DZ1/DE1(DY)” BNC, and set the swing for 0V to 3V.
Monitoring test points “TP18” (input), and “RB1 (RA)”
(output) with a scope allows evaluation of the total Tx and Rx
performance. In this configuration, the Tx output line
connects to an Rx input line, so the data driven on the Tx
input (DY) appears at the Rx output (RA).
Evaluating the Logic Supply (VL) Function
The ISL3331 includes a VLpin that powers the logic inputs
(Tx inputs and control pins) and Rx outputs, regardless of
protocol selection. These pins interface with “logic” devices
such as UARTs, ASICs, and µcontrollers, and today most of
these devices use power supplies significantly lower than
3.3V. Connecting the VLpin to the power supply of the logic
device limits the ISL3331’s Rx output VOH to VL, and
reduces the Tx and control input switching points to values
compatible with the logic device’s output levels. If the logic
device is also powered by 3.3V, then the VLpin should be
shorted to the VCC pin.
Removing jumper “VCC-VL” (16), and connecting a new
power supply to the “VL” banana jack allows the user to
evaluate this function. VLcan be anywhere from VCC down
to 1.2V, but the input switching points may not provide
enough noise margin when VL< 1.5V. Table 2 indicates
typical VIH and VIL values for various VLsettings so the user
can ascertain whether or not a particular VLvoltage meets
his needs.
To evaluate the VLimpact on Rx VOH, vary the VLvoltage
while monitoring a high Rx output. To evaluate the VLeffect
on input switching points, remove the “VL-VHIGH” (17)
jumper, connect a new supply between the “VHIGH” and
“GND” banana jacks, set the VLsupply to the desired
voltage, move the jumper of the input to be tested to the
“VH” position, and vary the “VHIGH” supply to determine the
switching point.
Jumper Definitions
The jumpers used to evaluate the ISL3331 are:
J-A1 (1) - Connects A1 input to GND through a 50Ωresistor.
J10 (2) - Connects A1 input to the RXBIAS jack.
J9 (3) - Connects B1 input to the RXBIAS jack.
J-B1 (4) - Connects B1 input to GND through a 50Ωresistor.
A1/Y1_LB (5) - Loops output Y1 back to input A1.
B1/Z1_LB (6) - Loops output Z1 back to input B1.
J-A2(485/232) (7) - “LOW” sets the IC to RS-232 mode;
“VH” sets it to RS-485 mode.
J-(DEN) (8) - “LOW” disables RS-232 or RS-485 Tx outputs;
“VH” enables all Tx outputs.
J-SPB (9) - Used with “SLEW” to set the RS-485 Tx data
rate (see Table 1).
J-RXEN1 (10) - “LOW” enables all RS-232 or RS-485 Rx
outputs; “VH” disables Rx outputs (if and only if
J-(RXEN) = “LOW”).
J-(RXEN) (11) - “LOW” disables all RS-232 or RS-485 Rx
outputs (if and only if J-RXEN1 = “VH”); “VH” enables Rx
outputs.
J-(ON) (12) - “LOW” places IC in “special features” mode
(loopback, SHDN, etc.); “VH” sets IC for normal operation.
J-DY1(DZ/SLEW) (13) - “LOW” sets the Z Tx input low in
RS-232 mode or selects the slew rate limited data rates in
RS-485 mode; “VH” sets the Z Tx input high in RS-232 mode
or selects the 20Mbps data rate in RS-485 mode.
TABLE 2. VIH AND VIL vs VLFOR VCC = 3.3V
VL
(V) VIH (V) VIL (V)
1.2 0.85 0.26
1.5 0.9 0.5
1.8 0.9 0.73
2.3 1.2 1.0
2.7 1.4 1.3
3.3 1.8 1.7
Application Note 1471

7AN1471.0
June 4, 2009
J-DZ1/DE1(DY) (14) - “LOW” sets the Y Tx input low in
RS-232 or RS-485 Modes; “VH” sets the Y Tx input high in
either mode.
RXBIAS-VCC (15) - Connects VCC to the “RXBIAS” jack; if
driving RXBIAS from a voltage other than VCC, remove this
jumper.
VCC-VL (16) - Connects VCC to the “VL” jack; if driving VL
from a voltage other than VCC, remove this jumper.
VL-VHIGH (17) - Connects VLto the “VHIGH” jack; if driving
VHIGH from a voltage other than VL, remove this jumper.
PCB Layout Information
The dimensions for the QFN land pattern used on this
evaluation board are shown in Figure 2.
FIGURE 2. QFN LAND PATTERN AND DIMENSIONS (in mm)
Application Note 1471

8
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
AN1471.0
June 4, 2009
FIGURE 3. JUMPER LOCATOR DIAGRAM
15
14
13
12
16
17
11
10
1
65
432
ISL3331EVAL1Z
7
8
9
Application Note 1471

9AN1471.0
June 4, 2009
1
40
2
3
4
5
6
7
8
9
10
30
29
28
27
26
25
24
23
22
21
39 38 37 36 35 34 33 32 31
11 12 13 14 15 16 17 18 19 20
NC NC NCC1- C1+ C2+ C2- VCC NC VL
V+
GND
GND V-
DEN2 (RXEN)
VHIGH
R18
R1, 3, 4, 8, 12, 15-18, 20, 24-26, 28 = 49.9Ω
J-(RXEN)
C8 C11
C12
C2-5 = 0.1µF (NOT POPULATED)
V+
V-
RXEN2 (NC)
VHIGH
R17
J-RXEN2 (NC)
TP12
TP10
RXEN1
VHIGH
R16
J-RXEN1
TP11
VHIGH
J-SPB
VHIGH
J-SPA (NC)
DEN1 (DEN)
VHIGH
R12
J-(DEN)
TP9
DY1 (DZ/SLEW)
VHIGH
R20
J-DY1 (DZ/SLEW)
TP20
R14
R7, 9 = 121Ω(NOT POPULATED)
R13
A2/Y2_LB
RXBIAS
J12
RXBIAS
J11
B2/Z2_LB
R11
R10
R5, 6, 10, 11 = 499Ω(NOT POPULATED)
R4
B2 (NC) TP8 J-B2
J4
VLOAD
C6
C3
Y2 (NC) TP3
C5
Z2 (NC) TP7
VHIGH
J-SEL2
VHIGH
J-SEL1
R7
RXBIAS
B1/Z1_LB
R5
J1
VLOAD
C1
R6
R1
B1 TP1 J-B1
C4
Y1 TP5
C2
Z1 TP2
R9
C7
RXBIAS
J9 J10
A1/Y1_LB
A1 TP6
R3
J-A1
VCC-VL
C10
C9
C22
C13
C9, 15, 17, 22, 27 = 10µF
P-VCC
VCC
GND
VL
P-GND
RXBIAS VHIGH VHIGH
RXBIAS
RXBIAS-VCC
C24
C25
C15
VL-VHIGH
C14
C23
C16
C17
VLOAD
VLOAD
C26
C27
J14
RA2(NC)
R23
R19, 22, 23, 27 = 1kΩ
C20
VLOAD
RB1(RA)
J6 R19 VLOAD
RA1(RB)
J13 R22
C19
VLOAD
J5
TP17
R27
C21
VLOAD
VHIGH
R26
J-(ON)
RB2 (ON)
VHIGH
R28
J-DZ2/DE2 (NC) DZ2/DE2 (NC)
TP21
VHIGH
R8
J-DY2 (NC)
DY2 (NC)
TP19
VHIGH
R25
J-ON/OFF (NC) ON/OFF (NC)
TP16
C18
VHIGH
R24
J-DZ1/DE1 (DY)
TP18
DZ1/DE1 (DY)
VHIGH
J-LB (NC)
A2 (485/232)
VHIGH
R15
J-A2 (485/232)
TP4
@
@
R13, 14 = 121Ω
C1, 6-8,10-14, 16, 18-21, 23-26 = 0.1µF
(to pin 27)
Application Note 1471