MAX3485ESA

MAX 3485ESA Features  3.3V power supply, half-duplex;  1/8 unit load allows up to 256 devices on the bus;  Driver output short-circuit protection function;  Over temperature protection function;  Low power shutdown function;  Receiver open circuit protection function;  Strong anti-noise ability;  Integrated transient voltage resistance function;  Transmission rate up to 12Mbps in an electrical noise environment; Description The MAX3485ESA is a 3.3V powered, half-duplex, low-power RS-485 transceiver that fully meets the requirements of the TIA/EIA-485 standard. The MAX3485ESA includes a driver and a receiver, both of which can be independently enabled and disabled. When both are disabled, both the driver and the receiver output a high impedance state. The MAX3485ESA has a 1/8 load that allows 256 MAX 3485ESA transceivers to be connected to the same communication bus. Error-free data transfer of up to 12Mbps is possible. The MAX3485ESA operates from a voltage range of 3.0 to 3.6V and features fail-safe, over temperature protection, current limit protection, over-voltage protection, and other functions. Pin configuration ● R RO 1 8 VCC RE B DE A DI 4 5 GND D Figure 1 MAX3485ESA pin configuration www.tw-gmc.com 1 MAX 3485ESA Limiting values Parameter Symbol Value Unit Supply voltage VCC +7 V Voltage of control port /RE, DE, DI -0.3~+7 V Bus side input voltage A, B -7~13 V Receiver output voltage RO -0.3~+7 V Operating temperature range -40~85 °C Storage temperature range -60~150 °C Welding temperature 300 °C 400 mW SOP8 Continuous power dissipation The maximum limit parameter value means that exceeding these values may cause irreversible damage to the device. Under these conditions, it is not conducive to the normal operation of the device. Continuous operation of the device under the maximum allowable rating may affect the reliability of the device. The reference point of all voltages is ground. Pin functions Pin number Pin name 1 RO 2 /RE 3 DE 4 DI 5 GND 6 A Non-inverting receiver input and non-inverting driver output 7 B Inverting receiver input and inverting driver output 8 VCC www.tw-gmc.com Pin function Receiver output When /RE is low level: if A-B ≧ 200mV, RO = high; if A-B ≦ -200mV, RO = low Receiver output enable control When /RE is low level, receiver output is enabled, and RO output is available. When /RE is high level, receiver output is disabled, and RO is in high impedance state. When /RE is high level and DE is low level, the device enters low power consumption mode. Driver output enable control When DE is high level, driver output is available; when DE is low level, the output is in high impedance state. When /RE is high level and DE is low level, the device enters low power consumption mode. Driver input When DE is high level, the DI low level forces the non-inverting driver output A low and inverting driver output B high; The DI high level forces the non-inverting driver output A high and inverting driver output B low. Ground Power supply 2 MAX 3485ESA Driver electrical characteristics Parameter Symbol Differential output voltage (no load) VOD1 Differential output voltage VOD2 Change in magnitude of differential output voltage (NOTE1) Common mode output voltage Change in magnitude of common mode output voltage (NOTE1) Test Conditions Min Typ Max 3.3 Unit V Figure 2, RL = 54 Ω 1.5 VCC Figure 2, R L = 100 Ω 2 VCC V ∆VOD Figure 2, R L = 54 Ω 0.2 V VOC Figure 2, RL = 54 Ω 3 V ∆VOC Figure 2, R L = 54 Ω 0.2 V Input high voltage VIH DE, DI, /RE Input low voltage VIL DE, DI, /RE Logic input current IIN1 DE, DI, /RE Output short-circuit current, short-circuit to high IOSD1 Short-circuit to 0V~12V Output short-circuit current, short-circuit to low IOSD2 Short-circuit to -7V~0V V 2.0 -2 0.8 V 2 μMAX/VSSOP8A 250 mA -250 mA Thermal shutdown threshold 140 °C Thermal shutdown hysteresis 20 °C (unless otherwise stated VCC=3.3V±10%, Temp=TMIN~TMAX, typical value is VCC=+3.3V, Temp＝25°C) NOTE1: ∆VOD and ∆VOC are the changes in VOD and VOC amplitude caused by a change of DI state of the input signal. Receiver electrical characteristics Parameter Input current (A, B) www.tw-gmc.com Symbol IIN2 Test Conditions Min DE = 0 V, VCC=0 or 3.3V VIN = 12 V DE = 0 V, VCC=0 or 3.3V VIN = -7 V 3 -100 Typ Max Unit 125 μMAX/VSSOP8A μMAX/VSSOP8A MAX 3485ESA Positive-going input threshold voltage VIT+ -7V ≦ VCM ≦ 12V Negative-going input threshold voltage VIT- -7V ≦ VCM ≦ 12V -200 Hysteresis voltage Vhys -7V ≦ VCM ≦ 12V 10 High level output voltage VOH IOUT = −2.5mA, VID = +200 mV VCC-1.5 Low level output voltage VOL IOUT = +2.5mA, VID = -200 mV 0.4 V Tristate leakage current IOZR 0.4V < V O < 2.4V ±1 μMAX/VSSOP8A Receiver input resistance RIN -7V ≦ VCM ≦ 12V 96 Receiver short-circuit current IOSR 0V ≤ VO ≤ VCC ±8 +200 mV mV 30 mV V kΩ ±60 mA (unless otherwise stated VCC=3.3V±10%, Temp=TMIN~TMAX, typical value is VCC=+3.3V, Temp＝25°C) Supply current Parameter Supply current Symbol Test conditions Typ Max Unit ICC1 /RE = 0V, DE = 0V 520 800 μMAX/VSSOP8A ICC2 /RE = VCC, DE = VCC 540 700 μMAX/VSSOP8A Typ Max Unit Min Driver switching characteristics Parameter Symbol Test conditions Driver differential output delay tDD 10 35 ns Driver differential output transition time RDIFF = 60 Ω, CL1=CL2=100pF tTD (see Figure 3 and Figure 4) 12 25 ns Driver propagation delay, low-to-high tPLH 8 35 ns Driver propagation delay, high-to-low tPHL 8 35 ns www.tw-gmc.com RDIFF = 27 Ω, (see Figure 3 and Figure 4) 4 Min MAX 3485ESA |tPLH -tPHL | tPDS Driver enable to output high tPZH Driver enable to output low tPZL Driver disable time from low tPLZ Driver disable time from high tPHZ Driver enable from shutdown to output high tDSH Driver enable from shutdown to output low tDSL 1 8 ns 20 90 ns 20 90 ns 20 80 ns 20 80 ns RL = 110Ω, (see Figure 5,6) 500 900 ns RL = 110Ω, (see Figure 5,6) 500 900 ns Typ Max Unit 80 150 ns 80 150 ns 7 10 ns RL = 110Ω, (see Figure 5, 6) RL = 110Ω, (see Figure 5,6) Receiver switching characteristics Parameter Symbol Receiver input to output delay (low to high) tRPLH Test Conditions Min CL=15pF See Figure 7 and Figure 8 Receiver input to output delay (high to low) tRPHL |tRPLH − tRPHL| tRPDS Receiver enable to output low tRPZL CL=15pF See Figure 7 and Figure 8 20 50 ns Receiver enable to output high tRPZH CL=15pF See Figure 7 and Figure 8 20 50 ns tPRLZ CL=15pF See Figure 7 and Figure 8 20 45 ns tPRHZ CL=15pF See Figure 7 and Figure 8 20 45 ns tRPSH CL=15pF See Figure 7 and Figure 8 200 1400 ns tRPSL CL=15pF See Figure 7 and Figure 8 200 1400 ns tSHDN NOTE2 300 ns Receiver disable time from low Receiver disable time from high Receiver enable from shutdown to output high Receiver enable from shutdown to output low Time to shutdown 80 NOTE2: The device is put into shutdown by bringing RE high and DE low. If the enable inputs are in this state for less than 80ns, the device is guaranteed not to enter shutdown. If the enable inputs are in this state for at least 300ns, the device is guaranteed to have entered shutdown. www.tw-gmc.com 5 MAX 3485ESA Function table Driver Control Receiver Input Output Control Input Output /RE DE DI A B /RE DE A-B RO X 1 1 H L 0 X ≥200mV H X 1 0 L H 0 X ≤-200mV L 0 0 X Z Z 0 X Open/shortcircuit H 1 0 X 1 X X Z Z (shutdown) X: don’t care; Z: high impedance www.tw-gmc.com X: don’t care; Z: high impedance 6 MAX 3485ESA Test circuit Fig. 2 Driver DC test load CL includes probe and stray capacitance (same as below) Fig. 3 Driver differential output delay and transition times Fig. 4 Driver propagation times www.tw-gmc.com 7 MAX 3485ESA Fig. 5 Driver enable and disable times Fig. 6 Driver enable and disable times www.tw-gmc.com 8 MAX 3485ESA Fig. 7 Receiver propagation delay Fig. 8 Receiver enable and disable times www.tw-gmc.com 9 MAX 3485ESA General description 1 Brief description The MAX3485ESA is a half-duplex high-speed transceiver for RS-485/RS-422 communication, and includes one driver and one receiver. It has fail-safe, over-voltage protection and over-current protection. The MAX3485ESA allows error-free data transmission up to 12Mbps. 2 Allowing up to 256 transceivers on the bus The standard RS-485 receiver has an input impedance of 12kΩ (1 unit load), and the standard driver can drive up to 32 unit loads. The receiver of the MAX3485ESA transceiver has a 1/8 unit load receiver input impedance (96kΩ), allowing up to 256 transceivers to be connected in parallel on one bus. These devices can be combined arbitrarily, or combined with other RS485 transceivers, as long as the total load does not exceed 32 units. 3 Driver output protection Two mechanisms are used to avoid faults or bus collisions that cause excessive output current and excessive power consumption. First, over-current protection provides fast short-circuit protection over the entire common-mode voltage range (refer to the typical operating characteristics). Second, the thermal shutdown circuit forces the driver output into a high-impedance state when the die temperature exceeds 140°C. 4 Typical applications 4.1 Bus networking: The MAX3485ESA RS485 transceiver is designed for bidirectional data communication on multi-point bus transmission lines. Figure 9 shows a typical network application circuit. These devices can also be used as linear repeaters with cables longer than 4000 feet. In order to reduce reflections, terminal matching should be done at both ends of the transmission line with their characteristic impedance, and the length of the branch wires other than the main line should be as short as possible. Fig. 9 Bus-type RS485 half-duplex communication network www.tw-gmc.com 10 MAX 3485ESA 4.2 Hand-in-hand networking: Also known as daisy chain topology, it is the standard and specification of RS485 bus wiring, and is the RS485 bus topology recommended by organizations such as TIA. The wiring method is that the master control device and multiple slave devices form a hand-in-hand connection, as shown in Figure 10, the hand-inhand way is to leave no branches. This wiring method has the advantages of low signal reflection and high communication success rate. Fig. 10 Hand-in-hand type RS485 half-duplex communication network 4.3 Bus port protection : In harsh environments, RS485 communication ports are usually protected against static electricity, lightning and surge protection, etc. and it is even necessary to prevent 380V power supply access to avoid damage of smart meters and industrial control hosts. Figure 11 shows 3 common kinds of RS485 bus port protection schemes. The first scheme is to connect the TVS device to the protection ground in parallel with the AB port, the TVS device in parrallel with the AB port, the thermistor in series with the AB port and the gas discharge tube is connected to the protection ground to form a three-level protection scheme. The second scheme is a three-level protection scheme including TVS connected to the ground in parallel with AB, the thermistor in series and the varistor in parallel with AB. The third one includes pull-down resistors connected to the power supply and ground respectively for AB, TVS between AB and the thermistor connected to A or B port. Fig. 11 Port protection scheme www.tw-gmc.com 11 MAX 3485ESA SOP-8 Symbol A A1 A2 b c D E E1 e L θ www.tw-gmc.com Dimensions In Millimeters Min Max 1.350 1.750 0.100 0.250 1.350 1.550 0.330 0.510 0.170 0.250 4.700 5.100 3.800 4.000 5.800 6.200 1.270(BSC) 0.400 1.270 0° 8° 12 Dimensions In Inches Min Max 0.053 0.069 0.004 0.010 0.053 0.061 0.013 0.020 0.006 0.010 0.185 0.200 0.150 0.157 0.228 0.244 0.050(BSC) 0.016 0.050 0° 8°