an1470

ISL3333EVAL1Z User’s Manual
®
Application Note
Description
The ISL3333EVAL1Z evaluation board is RoHS compliant,
and provides a quick and easy method for evaluating this
two-port Dual Protocol IC. The evaluation board also
accommodates the ISL3331; see the “ISL3331EVAL1Z
User’s Manual” for details.
This board was designed to allow the user to evaluate all the
features available on the ISL3332 and ISL3333 products.
The ISL3333 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 ISL3332. The same die is used in both
products, so other than minor package effects, evaluating
the QFN packaged ISL3333 is a reasonable substitute for
evaluating the ISL3332.
By changing jumper positions the user can quickly set the
board to evaluate any of the ISL3333’s many modes and
features, and the input states can also be set via jumpers.
Refer to the ISL3333 data sheet for complete details
regarding the functions and features of this device. These
dual protocol ICs feature many modes. However, 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
- Active Low RS-232 Tx Disable Function
• Quick Configuration Using Jumpers
• State of All Inputs Can be Set by Jumper Positions
• No Bus Termination Resistors on Port 1 Allows Easy
RS-232 Evaluation; Bus Termination Resistors on Port 2
for RS-485 Evaluation
• Simple Operation Requires Only One, 3.3V Power Supply
Important Notes
June 3, 2009
AN1470.0
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”), and a name that applies to only
the ISL3333 is followed by “(NC)” (e.g., “B2 (NC)”).
It is important to note that the ISL333x do not follow the
RS-485 convention whereby the inverting I/O is labeled
“B/Z”, and the non-inverting I/O is “A/Y”. Thus, the ISL3332
and ISL3333 A/Y (B/Z) pins connect to the B/Z (A/Y) pins of
generic RS-485/422 ICs.
Input signals that connect to a BNC connector, because they
are likely to be driven by a generator, include a 50Ω
termination resistor to GND when the jumper is in the “LOW”
position.
Port 1 includes no Rx input nor Tx output termination
resistors, as this port is intended for RS-232 evaluation.
Port 2, intended for RS-485/422 evaluation, includes 120Ω
differential termination resistors across the Rx inputs, and
across the Tx outputs.
Default Configuration
As delivered (see “Functional Diagram (Default
Configuration)” on page 2), the board is configured for Port 1
in RS-232 mode with Tx and Rx enabled, Rx inputs floating,
and Tx inputs low. Port 2 is in RS-485 mode with Tx and Rx
enabled, Tx set for high speed (20Mbps) operation, driver
input (DY) low, Rx inputs floating but shorted together
through a 120Ω termination resistor. Additionally, the
ISL3333 is powered-up (i.e., not SHDN), has internal
loopback disabled, and has VL shorted to VCC. To achieve
this configuration, the jumpers (see “Jumper Definitions” on
page 7) are installed as follows (unlisted jumpers are not
installed, and (#) indicates the jumper number on Figure 3
jumper locator): SEL1 (7) = LOW; SEL2 (8) = VH;
(DEN) (28) = VH; RXEN1 (15) = LOW; SPA (16) = VH;
SPB (17) = VH; RXEN2 (18) = LOW; (RXEN) (29) = VH;
DE2 (19) = VH; DY2 (20) = LOW; ON/OFF (21) = VH;
LB (22) = VH; DY1 (DZ/SLEW) (23) = LOW;
DZ1/DE1 (DY) (24) = LOW; RXBIAS-VCC (25) = installed;
VCC-VL (26) = installed; VL-VHIGH (27) = installed.
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 “Jumper Definitions” on page 7 for a
description of the function of each jumper.
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Application Note 1470
Functional Diagram (Default Configuration)
+3.3V
C1
0.1µF
C2
0.1µF
(27)
(26)
+ 0.1µF
34
37
C1+ VCC
+
38
C136
C2+
+
35
C22 A1
5kΩ
VHIGH (VH)
31
VL
V+
1
V- 19
5kΩ
RA1 29
R
R
4 Y1
RB1 30
D
5 Z1
120Ω
D
VH
VH
DZ1 28
ON/OFF
10 B2
R
8
13
14
VH
SEL1
7
SEL2
20
DEN2
11 A2
LB
Z2
D
VH
VH
RA2 22
RXEN2
DY2 24
DE2 23
SPA
SPB
25
26
18
9 Y2
120Ω
VH
GND
15, 16
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 - R5, R6,
R10, R11 - are 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 ((2), (3), (11), (12)); the “RXBIAS-VCC”
(25) 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” (27) jumper shorts this jack to VL, so remove
this jumper if supplying a voltage other than VL.
2
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, in order for ICC
to be monitored. Ensure that the “RXBIAS-VCC” (25),
“VCC-VL” (26) and “VL-VHIGH” (27) jumpers are installed in
the upper right hand corner of the board.
DY1 27
DEN1 12
VH
VH
C4
0.1µF
+
RXEN1 17
3 B1
6
+C3
0.1µF
VL - The logic supply voltage that sets the ISL3333’s Rx
output VOH levels, and the logic and Tx input switching
points; the “VCC-VL” (26) jumper shorts this jack to VCC, so
remove this jumper if supplying a voltage other than VCC.
For simplicity, the following discussions assume that Port 1
is used for RS-232 evaluations, and Port 2 for RS-485
evaluations. Of course, the user is free to configure either
port for either protocol.
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) for Port 1, and
jumpers “A2/Y2_LB” (10) and “B2/Z2_LB” (9) for Port 2. 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.
Basic RS-485 DC Evaluation (Port 2)
GENERAL OBSERVATIONS
ICC should be approximately 23mA. Most of this current is
due to the RS-485 Tx driving the 120Ω termination resistor
(R13). To get just the quiescent ISL3333 ICC, simply move
jumper “DE2” (19) to the "LOW" position. ICC should now be
approximately 3.9mA, due to the charge pumps running to
provide the RS-232 transmitter supplies for Port 1. Move
jumper “DE2” back to the “VH” position.
Measure V+ and V- at the banana jacks - V+ ≈ +6V and
V- ≈ -5.7V, indicating that the charge pumps are on. If both
ports were programmed for RS-485 mode, then ICC drops to
1.2mA (if “DE2” = “LOW”), and V+ ≈ VCC, V- = GND.
RA2 is high (due to the “full failsafe” Rx) while RB2 is
tri-stated, but pulled high by a weak internal current source,
because it is unused in RS-485 mode.
RECEIVER TESTS
The “full failsafe” nature of the Rx can be evaluated by
manipulating the “A2 (485/232)” (14) and “B2” (13) input
jumpers. In the default configuration, A2 and B2 are
“shorted” via a 120Ω termination resistor, but RA2 (measure
at the “RA2 (NC)” test point, located between test points
“TP17” and “TP21”) remains high due to the failsafe
“terminated but undriven” functionality. Installing jumpers
“A2” (14) (to the “LOW” position) and “B2” effectively shorts
the two inputs together (i.e., VID = VB2 - VA2 = 0). RA2 still
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Application Note 1470
remains high, indicating that the Rx is also failsafe “shorted”.
Failsafe “open” is best demonstrated using Port 1. Simply
move the “SEL1” (7) jumper to the VH position to place
Port 1 in RS-485 mode (note that ICC drops to 1.1mA, if
“DE2” is “LOW”). In this configuration, A1 and B1 float (5kΩ
pull-down resistors only connect in RS-232 mode), but RA1
(measure at the “RA1 (RB)” test point to the left of jumper
(24)) remains high due to the failsafe “open” functionality.
This combination of failsafe “open”, “shorted”, and
“terminated but undriven” yields a “full-failsafe” Rx. Switch
the “SEL1” jumper back to the "LOW" position.
To switch the port 2 Rx output state leave the “B2” jumper
installed, remove the “A2” jumper, and install the A2 Rx bias
jumper, “J12” (11). The “RXBIAS-VCC” (25) jumper now
drives the A2 input voltage to VCC, which switches RA2 low.
Removing the “RXBIAS-VCC” jumper, and connecting a
power supply between the “RXBIAS” banana jack and GND
now sets the Rx differential input voltage, via A2, and varying
this supply switches the Rx output state. For example, with
the RXBIAS supply = 0V (VID = 0V) RA2 is high, and
increasing RXBIAS to at least +200mV (VID = -200mV)
switches the output low. When finished, remove jumper
“J12”.
To disable the RA2 output via the active low RXEN2 pin,
move jumper “RXEN2” (18) to the “VH” position. Note that
the RB2 internal current source still keeps this output high.
Move the “RXEN2” jumper back to the “LOW” position,
remove the “RXBIAS” power supply and the “B2” jumper,
and reinstall the “RXBIAS-VCC” (25) jumper.
DRIVER TESTS
Tx DC output levels are independent of Tx speed setting. In
the default configuration, the driver input, DY2, is low, so the
Tx non-inverting output, Z2, is low (≈0.8V), while the
inverting output, Y2, is high (≈3.1V). To switch the output
states, simply move the “DY2” (20) jumper to the “VH”
position. In either state, note the differential output voltage
(VOD) of ≈2.3V into the 120Ω load. To evaluate the double
terminated VOD (≈2.0V), configure Port 2 for “external
loopback”, as described previously (i.e., install jumpers (9)
and (10)).
To disable the Tx output via the active high DE2 pin, move
the “DE2” (19) jumper from the “VH” to the “LOW” position.
When finished, return the “DE2” jumper to the “VH” position,
return the “DY2” jumper to the “LOW” position, and remove
the “external loopback” jumpers.
INTERNAL LOOPBACK
Before enabling loopback mode, note that the RA2 output is
high. To configure the ISL3333 for internal loopback, simply
move jumper “LB” (22) from the “VH” to the “LOW” position.
Note that ICC increases by ≈3mA, due to the enabling of the
loopback receivers, and note that the LB pin controls both
ports. RA2 is now low due to the Tx outputs internally driving
3
the Rx. You can repeat the previous Rx switching tests to
confirm that the external Rx input pins now have no affect on
RA2.
When finished, return the “LB” jumper to the “VH” position.
LOW POWER SHDN
SHDN automatically powers down both ports, shuts off the
charge pumps (V+ collapses to VCC, V- to GND), disables
the Tx and Rx outputs, and places the ISL3333 in it’s lowest
power mode. Before entering SHDN, remove the “ON/OFF
(NC)” (21) jumper, and note that the pin’s on-chip pull-up
resistor keeps the ISL3333 powered-up. To enter SHDN,
move the “ON/OFF (NC)” jumper from the “VH” to the “LOW”
position. In the default configuration, the ICC drops to 22µA.
Return the “ON/OFF” jumper to the “VH” position.
Basic RS-485 AC Evaluation
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.
Due to the Rx differential termination resistor (R14) across
A2 and B2, the easiest way to evaluate the Rx by itself is by
using Port 1. Move the “SEL1” (7) jumper to the “VH”
position to set Port 1 to RS-485 mode.
Add jumper “B1” (4) to connect that input to GND, and add
jumper “A1” (1) to engage the 50Ω term. Connect a
generator to the “A1” BNC, and set it for a -1.5V to +1.5V
swing. Monitoring test points “TP6” (input), and “RA1(RB)”
(output) with a scope allows the Rx prop delays and skews
to be measured. If desired, you can load the Rx output with a
1kΩ resistor by adding jumper “J13” (not numbered), located
below, and left of, test point “RA1 (RB)”. 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 low RXEN1 pin. From the
previous jumper configuration, leave the “B1” and “J13”
jumpers installed, remove the “A1” jumper, and install the A1
Rx bias jumper, “J10” (2). Connect the “VLOAD” jack to VCC,
switch the “RXEN1” (15) jumper to the low position to
engage the 50Ω term, set the generator to swing from 0V to
3V, and move the generator to the “RXEN1” BNC.
Monitoring test points “TP11” (input), and “RA1(RB)” (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.
TX SPEED SELECTION
Before performing any driver AC evaluation, ensure that all
jumpers are in their default positions, and then configure the
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Application Note 1470
“SPA” (16) and “SPB” (17) jumpers for the desired Tx speed
setting. Table 1 details the jumper settings for each of the
speed options.
TABLE 1. JMPR SETTINGS FOR Tx SPEED SELECTION
DATA RATE
J-SPA (16)
J-SPB (17)
115kbps
“LOW”
“VH”
460kbps
“LOW”
“LOW”
20Mbps
“VH”
“LOW” or “VH”
DRIVER TESTS (PORT 2)
R13 provides a differential 120Ω load across the driver
outputs, and, if desired, a differential capacitive load may be
soldered on top of R13. Alternatively, single ended (Y2 or Z2
to GND) resistive and/or capacitive loads may be added at
positions “C3” and “C5”, if so desired.
Ensure that the “DY2” (20) jumper is in the “LOW” position to
engage the 50Ω term resistor, connect the generator to the
“DY2 (NC)” BNC, and set the swing for 0V to 3V. Monitoring
test points “TP19” (input), and “TP3” and “TP7” (Y2 and Z2
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
“DZ2/DE2 (NC)” (19) jumper to the “LOW” position to
engage its 50Ω term resistor. Connect the generator to the
“DZ2/DE2 (NC)” BNC, and set the swing for 0 to 3V.
Monitoring test points “TP21” (input), and “TP3” and “TP7”
(Y2 and Z2 outputs respectively) with a scope allows the
enable and disable times to be measured. Note that the
differential termination resistor collapses the disabled
outputs.
EVALUATING DRIVER AND RECEIVER COMBINED
PERFORMANCE
Start with the default jumper configuration. Performance
through a cascaded Tx and Rx can easily be evaluated,
utilizing the external loopback function, by installing jumpers
“A2/Y2_LB (10) and “B2/Z2_LB (9). In this configuration, the
Tx output lines connect to the corresponding Rx input lines,
so the data driven on the Tx input (DY2) appears at the Rx
output (RA2).
DIfferential 120Ω resistors R13 and R14 allow evaluation of
the Tx performance while driving a double terminated load.
INTERCONNECTING DRIVER AND RECEIVER WITH A
CABLE
To evaluate the performance of the Tx and Rx (Port 2)
interconnected by a cable, start with the default
configuration, connect one wire of a twisted pair between
test points “TP7” and “TP8”, and connect the other wire in
the pair between “TP3” and “TP4”. Ensure that the “DY2
(NC)” (20) jumper is in the “LOW” position to engage the
4
50Ω term resistor, connect the generator to the “DY2 (NC)”
BNC, and set the swing for 0V to 3V. Monitoring test points
“TP19” (input), and test point “RA2 (NC)” (Rx output)
illustrates the overall input to output performance.
Resistors R14 and R13 provide source and load terminations
for the cable.
Basic RS-232 DC Evaluation (Port 1)
GENERAL OBSERVATIONS
To better evaluate the RS-232 mode ICC, it is a good idea to
disable the RS-485 drivers by moving jumper “DZ2/DE2
(NC)” (19) to the "LOW" position. ICC should be
approximately 3.9mA after this change.
Note that RS-232 drivers and receivers are inverting by
definition.
Don’t use Port 2 for RS-232 evaluation without removing the
input and output differential termination resistors (R13 and
R14), or the RS-232 waveforms will be severely distorted.
RECEIVER TESTS
In the default configuration - (see “Functional Diagram
(Default Configuration)” on page 2) - RA1 (measure at the
“RA1(RB)” test point to the left of jumper (24)) and RB1
(measure at the “RB1(RA)” test point to the right of jumper
(1)) are high due to the A1 and B1 5kΩ input resistors to
GND.
To switch the port 1 Rx output states, install the A1 and B1
Rx bias jumpers, “J10” (2) and “J9” (3). The “RXBIAS-VCC”
(25) jumper now drives the Rx input voltages to VCC, which
switches RA1 and RB1 low. Removing the “RXBIAS-VCC”
jumper and connecting a power supply between the
“RXBIAS” banana jack and GND, allows this supply to set
the Rx input voltages, in case the user wants to evaluate the
Rx switching points. When finished, remove jumpers “J10”
and “J9”.
To disable the Rx outputs via the active low RXEN1 pin,
move jumper “RXEN1” (15) to the “VH” position.
Return the “RXEN1” jumper to the “LOW” position, remove
the “RXBIAS” power supply, and reinstall the “RXBIAS-VCC”
jumper.
DRIVER TESTS
The RS-232 Tx outputs, Y1 and Z1, are high (≈ 6.2V) in the
default configuration, because DY1 and DZ1 are low. To
switch the output states (VOL ≈ -5.7V), simply move the
“DY1 (DZ/SLEW)” (23) and “DZ1/DE1 (DY)” (24) jumpers to
the “VH” position. To evaluate the loaded driver output
voltages, configure Port 1 for “external loopback”, as
described previously (i.e., install jumpers (5) and (6)). Each
driver output is now loaded by an Rx input resistor, and the
output voltages still exceed ±5.5V.
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Application Note 1470
The Tx outputs are disabled in SHDN, or by driving
DEN1(DEN) low (move jumper (DEN) (28) to the “LOW”
position).
Remove the “external loopback” jumpers when finished, and
switch the “DY1 (DZ/SLEW)” and “DZ1/DE1 (DY)” jumpers
back to the “LOW” positions, and the (DEN) jumper back to
the “VH” position.
INTERNAL LOOPBACK
Before enabling loopback mode, note that the RA1 and RB1
outputs are high. To configure the ISL3333 for internal
loopback, simply move jumper “LB” (22) from the “VH” to the
“LOW” position. Note that ICC increases by ≈4.5mA, due to
the enabling of the loopback receivers, and note that the LB
pin controls both ports. RA1 and RB1 are 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 the Rx outputs. Switching
the state of jumpers “DY1 (DZ/SLEW)” (23) and
“DZ1/DE1 (DY)” (24) will toggle RA1 and RB1 accordingly.
When finished, return the “LB” jumper to the “VH” position.
LOW POWER SHDN
SHDN automatically powers down both ports, shuts off the
charge pumps (V+ collapses to VCC, V- to GND), disables
the Tx and Rx outputs, and places the ISL3333 in it’s lowest
power mode. To enter SHDN, move the “ON/OFF” (21)
jumper from the “VH” to the “LOW” position. In the default
configuration, the ICC drops to 22µA.
Basic RS-232 AC Evaluation (Port 1)
Before starting, ensure that the jumpers are back in the
default positions, with the “DZ2/DE2” (19) jumper in the
“LOW” position. 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 50Ω term, connect a
generator to the “A1” BNC, and set it for at least a 0V to 3V
swing. Monitoring test points “TP6” (input), and “RA1 (RB)”
(output) with a scope allows the Rx prop delays and skews
to be measured. If desired, you can load the Rx output with a
1kΩ resistor by adding jumper “J13” (not numbered), located
below, and left of, test point “RA1 (RB)”. 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 low RXEN pin, start from the previous
jumper configuration, leave the “J13” 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),
ensure the “RXEN1” (15) jumper is in the low position to
engage the 50Ω term, set the generator to swing from 0V to
5
3V, and move the generator to the “RXEN1” BNC.
Monitoring test points “TP11” (input), and “RA1(RB)” (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), and
connect the “VLOAD” banana jack to VCC.
DRIVER TESTS
Ensure that the “DY1 (DZ/SLEW)” (23) jumper is in the
“LOW” position to engage the 50Ω term resistor, connect the
generator to the “DY1 (DZ/SLEW)” BNC, and set the swing
for 0 to 3V. Monitoring test points “TP20” (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 add the “A1/Y1_LB” (5) jumper,
which connects an Rx input, including its 5kΩ pull-down, to
the driver output. Capacitive loading can be added at
position C4.
To measure the Y1 Tx enable/disable time to/from a high
output state via the active high DEN1 pin, start from the
previous jumper configuration, and ensure that the
“DY1 (DZ/SLEW)” jumper is in the “LOW” positions. Ensure
that the “(DEN)” (28) jumper is in the “LOW” position to
engage the 50Ω term resistor, and connect the generator
(set for a 0 to 3V swing) to the “DEN1(DEN)” BNC.
Monitoring test points “TP9” (input) and “TP5” (output) with a
scope, allows the measuring of the enable and disable
times. To evaluate the Tx enable/disable time to/from a low
output state, move jumper “DY1 (DZ/SLEW)” to the “VH”
position.
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
“RXEN1” (15) and “DY1 (DZ/SLEW)” (23) jumpers are set to
the “LOW” position, and that the “(DEN) (28) jumper is in the
“VH” position. Connect the generator to the
“DY1 (DZ/SLEW)” BNC, and set the swing for 0V to 3V.
Monitoring test points “TP20” (input), and “RA1 (RB)”
(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 ISL3333 includes a VL pin 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 VL pin to the power supply of the logic
device limits the ISL3333’s Rx output VOH to VL, and
reduces the Tx and control input switching points to values
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Application Note 1470
compatible with the logic device’s output levels. If the logic
device is also powered by 3.3V, then the VL pin should be
shorted to the VCC pin.
To evaluate the VL pin performance, remove the “VCC-VL”
(26) jumper, and connect a supply between the “VL” and
“GND” banana jacks. VL can 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 VL values so the user can
ascertain whether or not a particular VL voltage meets his
needs.
TABLE 2. VIH AND VIL vs VL FOR VCC = 3.3V
solder a capacitor across the C3 and C5 pads that connect
to Y2 and Z2, respectively.
Connect a generator to the “B1” BNC connector, and drive
the input from 0V to 3V at a data rate up to 400kbps
(generator period ≥ 5µs). The data will loop through the
RS-232 Rx, to the RS-485 Tx, to the RS-485 Rx, and back
through the RS-232 Tx, appearing at the “Y1” output back in
RS-232 form.
To evaluate the performance with the RS-485 Tx driving a
cable, remove the port 2 external loopback jumpers, and
connect a twisted pair cable from “Y2” (“TP3”) and “Z2”
(“TP7”) to “A2 (485/232)” (“TP4”) and “B2” (“TP8”)
respectively.
VL
(V)
VIH
(V)
VIL
(V)
1.2
0.85
0.26
0.9
0.5
C1
0.1µF
+
C1+
1.5
0.73
C2
0.1µF
+
C1C2+
1.8
0.9
2.3
1.2
1
2.7
1.4
1.3
3.3
1.8
1.7
+3.3V
NC
TxD
RS-232 IN
+ 0.1µF
VCC
C2A1
5kΩ
B1
5kΩ
To evaluate the VL impact on Rx VOH, vary the VL voltage
while monitoring a high Rx output. To evaluate the VL effect
on input switching points, remove the “VL-VHIGH” (27)
jumper, connect a new supply between the “VHIGH” and
“GND” banana jacks, set the VL supply 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.
RxD
RS-232 OUT
V-
C4
0.1µF
+
NC
RB1
D
DY1
DEN1
D
SEL1
DZ1
ON/OFF
DEN2
SEL2
A2
Connecting the ISL3333 as an RS-232 to RS-485
Converter
6
R
Y1
B2
+C3
0.1µF
RXEN1
Z1
VL
V+
RA1
R
NC
RS-485 IN
This two port dual protocol IC is ideal for implementing a two
wire (RxD and TxD) RS-232 to RS-485 converter, as shown
in Figure 1. To evaluate this circuit using the evaluation
board (starting with the default configuration): install the “B1”
(4) jumper to connect the 50Ω termination on the input;
remove the “DY1 (DZ/SLEW)” (23) and “DY2 (NC)” (20)
jumpers; connect a wire from the “RB1 (RA)” test point to the
DY2 test point (“TP19“); connect a wire from the “RA2 (NC)”
test point to the DY1 test point (“TP20”); connect the port 2
“external loopback” jumpers (9 and 10), and move the “SPA”
(16) and “SPB” (17) jumpers to the “LOW” positions to set
the RS-485 Tx speed to the medium data rate option. Note
that the RS-232 Tx output (Y1) is unloaded in this
configuration, while the RS-485 Tx output drives a double
terminated load (R13 and R14). The RS-232 output can be
resistively loaded by looping it back to the “A1” input via the
“A1/Y1_LB” (5) jumper, and can be capacitively loaded by
soldering the desired load value in position C4. To add a
differential capacitive load to the RS-485 driver, simply
solder the capacitor on top of termination resistor R13, or
VL
R
VL
RA2
RXEN2
Y2
RS-485 OUT
Z2
D
DY2
DE2
VL
GND
FIGURE 1. SINGLE IC RS-232 TO RS-485 CONVERTER
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Application Note 1470
Jumper Definitions
The jumpers used to evaluate the ISL3333 are (ordered by
red jumper numbers):
J-DZ2/DE2 (NC) (19) - “LOW” disables port 2 Tx in RS-485
mode, or sets the Z Tx input low in RS-232 Mode; “VH”
enables port 2 Tx in RS-485 mode, or sets the Z Tx input
high in RS-232 Mode.
J-A1 (1) - Connects A1 input to GND through a 50Ω resistor.
J-DY2 (NC) (20) - Sets the state of the port 2 DY Tx input.
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 50Ω resistor.
A1/Y1_LB (5) - Loops output Y1 back to input A1.
B1/Z1_LB (6) - Loops output Z1 back to input B1.
J-SEL1 (NC) (7) - “VH” sets port 1 to RS-485 mode; “LOW”
sets it to RS-232 mode.
J-SEL2 (NC) (8) - “VH” sets port 2 to RS-485 mode; “LOW”
sets it to RS-232 mode.
B2/Z2_LB (9) - Loops output Z2 back to input B2.
A2/Y2_LB (10) - Loops output Y2 back to input A2.
J- ON/OFF (NC) (21) - “LOW” places IC in low power SHDN;
“VH” sets IC for normal operation.
J- LB (NC) (22) - “LOW” enables internal loopback; “VH”
disables it.
J- DY1 (DZ/SLEW) (23) - Sets the state of the port 1 DY Tx
input.
J- DZ1/DE1 (DY) (24) - “LOW” disables port 1 Tx in RS-485
mode, or sets the Z Tx input low in RS-232 Mode; “VH”
enables port 1 Tx in RS-485 mode, or sets the Z Tx input
high in RS-232 Mode.
RXBIAS-VCC (25) - Connects VCC to the “RXBIAS” jack; if
driving RXBIAS from a voltage other than VCC, remove this
jumper.
J12 (11) - Connects A2 input to the RXBIAS jack.
J11 (12) - Connects B2 input to the RXBIAS jack.
VCC-VL (26) - Connects VCC to the “VL” jack; if driving VL
from a voltage other than VCC, remove this jumper.
J-B2 (13) - Connects B2 input to GND through a 50Ω
resistor.
VL-VHIGH (27) - Connects VL to the “VHIGH” jack; if driving
VHIGH from a voltage other than VL, remove this jumper.
J-A2 (485/232) (14) - “LOW” connects A2 input to GND
through a 50Ω resistor; “VH” connects A2 to the “VHIGH”
jack.
J-(DEN) (28) - Sets the DEN1 state. “LOW” disables the
port 1 Tx outputs if port 1 is set to RS-232 mode. “VH”
enables the port 1 RS-232 Tx.
J-RXEN1 (15) - “LOW” enables port 1 Rx; “VH” disables Rx.
J-(RXEN) (29) - Sets the DEN2 state. “LOW” disables the
port 2 Tx outputs if port 2 is set to RS-232 mode. “VH”
enables the port 2 RS-232 Tx.
J-SPA (NC) (16) - Used with SPB to set the RS-485 Tx data
rate (see Table 1).
J-SPB (17) - Used with SPA to set the RS-485 Tx data rate
(see Table 1).
J-RXEN2 (NC) (18) - “LOW” enables port 2 Rx; “VH”
disables Rx.
PCB Layout Information
The dimensions for the QFN land pattern used on this board
are shown in Figure 2.
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
7
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Application Note 1470
FIGURE 2. QFN LAND PATTERN AND DIMENSIONS (in mm)
26
25
27
1
2
3
24
4
7
22
9
8
23
5
6
21
10
13
20
12 11
16
19
17
14
15
18
29
28
ISL3333EVAL1Z
FIGURE 3. JUMPER LOCATOR DIAGRAM
8
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Application Note 1470
B1
J-B1
VLOAD
J-A1
R1
VLOAD
C18
C24
C14
C25
C23
C15 VCC
C16
C26
R3
P-VCC
J13
R22
VLOAD
RA1(RB)
C19
VHIGH
VL
C27
Y1
R19
RB1(RA)
VLOAD
TP6
A1
J6
VHIGH
P-GND
J10
J9
TP1
VHIGH
GND
RXBIAS
RXBIAS
C17
DZ1/DE1 (DY)
RXBIAS
RXBIAS
TP18
C22
J-DZ1/DE1 (DY)
TP5
V+
C4
C9
C13
RXBIAS-VCC
TP2
Z1
VL-VHIGH
R24
C10
C7
C8
VHIGH
C11
C2
A1/Y1_LB
VLOAD
B1/Z1_LB
J1
C1
R5
1
40
39
32
31
NC
NC C1- C1+ C2+ C2- VCC NC NC
VL
38
37
36
35
34
33
TP16
30
V+
2
29
3
28
R25
R9
VHIGH
VHIGH
4
27
5
26
6
25
7
24
J-DY2 (NC)
J-LB (NC)
R7
DY2 (NC)
TP19
@
VHIGH
ON/OFF (NC)
J-ON/OFF (NC)
VCC-VL
R6
R8
J-SEL1
VHIGH
TP21
R10
8
23
9
22
J14
R13
VHIGH
R11
10
GND GND
11
12
13
14
15
16
18
19
20
VHIGH
J5
DEN2 (RXEN)
C12
VHIGH
A2/Y2_LB
J-(RXEN)
VHIGH
J12
TP17
C21
TP12
R18
V-
VHIGH
VHIGH
RXEN2 (NC)
TP7
J-SPA (NC)
Z2 (NC)
C5
VLOAD
R27
J-SPB
RXBIAS
C6
R28
C20
V17
R14
J4
VLOAD
21
J11
VLOAD
R23
RA2(NC)
RXBIAS
B2/Z2_LB
J-SEL2
DZ2/DE2 (NC)
J-DZ2/DE2 (NC)
VHIGH
J-RXEN2 (NC)
VHIGH
RXEN1
J-RXEN1
TP10
RB2 (ON)
J-(ON)
R17
R26
TP11
TP4
A2 (485/232)
Y2 (NC)
TP3
R16
J-A2 (485/232)
C3
VHIGH
@
R15
VHIGH
B2 (NC)
(to pin 27)
TP20
TP8
J-B2
J-DY1 (DZ/SLEW)
R4
R20
9
DEN1 (DEN)
J-(DEN)
R1, 3, 4, 8, 12, 15-18, 20, 24-26, 28 = 49.9Ω
DY1 (DZ/SLEW) R5, 6, 10, 11 = 499Ω (NOT POPULATED)
R7, 9 = 121Ω (NOT POPULATED)
R13, 14 = 121Ω
R19, 22, 23, 27 = 1kΩ
C1, 6-8,10-14, 16, 18-21, 23-26 = 0.1µF
C2-5 = 0.1µF (NOT POPULATED)
C9, 15, 17, 22, 27 = 10µF
TP9
R12
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June 3, 2009
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