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. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2008. All Rights Reserved All other trademarks mentioned are the property of their respective owners. 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 AN1470.0 June 3, 2009 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 AN1470.0 June 3, 2009 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. AN1470.0 June 3, 2009 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 AN1470.0 June 3, 2009 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 AN1470.0 June 3, 2009 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 AN1470.0 June 3, 2009 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 AN1470.0 June 3, 2009 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 AN1470.0 June 3, 2009