A3953 Full-Bridge PWM Motor Driver Discontinued Product This device is no longer in production. The device should not be purchased for new design applications. Samples are no longer available. Date of status change: January 30, 2012 Recommended Substitutions: For existing customer transition, and for new customers or new applications, refer to the A4973. NOTE: For detailed information on purchasing options, contact your local Allegro field applications engineer or sales representative. Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use. A3953 Full-Bridge PWM Motor Driver Features and Benefits Description ▪ ±1.3 A continuous output current ▪ 50 V output voltage rating ▪ 3 V to 5.5 V logic supply voltage ▪ Internal PWM current control ▪ Saturated sink drivers (below 1 A) ▪ Fast and slow current-decay modes ▪ Automotive capable ▪ Sleep (low current consumption) mode ▪ Internal transient-suppression diodes ▪ Internal thermal shutdown circuitry ▪ Crossover current and UVLO protection Designed for bidirectional pulse width modulated (PWM) current control of inductive loads, the A3953 is capable of continuous output currents to ±1.3 A and operating voltages to 50 V. Internal fixed off-time PWM current-control circuitry can be used to regulate the maximum load current to a desired value. The peak load current limit is set by the user’s selection of an input reference voltage and external sensing resistor. The fixed off-time pulse duration is set by a user- selected external RC timing network. Internal circuit protection includes thermal shutdown with hysteresis, transient-suppression diodes, and crossover current protection. Special power-up sequencing is not required. Packages: Package B, 16-pin DIP with exposed tabs Package LB, 16-pin SOIC with internally fused pins Not to scale With the ENABLE input held low, the PHASE input controls load current polarity by selecting the appropriate source and sink driver pair. The MODE input determines whether the PWM current-control circuitry operates in a slow current-decay mode (only the selected source driver switching) or in a fast current-decay mode (selected source and sink switching). A user-selectable blanking window prevents false triggering of the PWM current-control circuitry. With the ENABLE input held high, all output drivers are disabled. A sleep mode is provided to reduce power consumption. Continued on the next page… 6 V CC 15 10 LOAD SUPPLY OUT A 9 OUT B LOGIC SUPPLY LOAD SUPPLY Functional Block Diagram 16 SLEEP & STANDBY MODES MODE 14 PHASE 7 V BB BRAKE 1 PWM LATCH R 11 – 8 + ENABLE INPUT LOGIC UVLO & TSD SENSE Q S BLANKING GROUND 4 V CC RS RC 3 5 12 + – 2 REF RT CT 13 GROUND V TH Dwg. FP-036-2A 29319.8I A3953 Full-Bridge PWM Motor Driver Description (continued) When a logic low is applied to the BRAKE input, the braking function is enabled. This overrides ENABLE and PHASE to turn off both source drivers and turn on both sink drivers. The brake function can be used to dynamically brake brush DC motors. and a 16-pin plastic SOIC with copper heat-sink tabs. For both package styles, the power tab is at ground potential and needs no electrical isolation. Each package type is available in a lead (Pb) free version (100% matte tin plated leadframe). The A3953 is supplied in a choice of two power packages; a 16-pin dual-in-line plastic package with copper heat-sink tabs, Selection Guide Part Number A3953SB-T A3953SLBTR-T Package 16-pin DIP with exposed thermal tabs 16-pin SOICW with internally-fused pins Packing 25 pieces per tube 1000 pieces per reel Absolute Maximum Ratings Characteristic Symbol Rating Units 50 V VCC 7.0 V VIN –0.3 to VCC + 0.3 V VCC = 5.0 V 1.0 V VCC = 3.3 V 0.4 V Output current rating may be limited by duty cycle, ambient temperature, and heat sinking. Under any set of conditions, do not exceed the specified current rating or a junction temperature of 150°C. ±1.3 A Load Supply Voltage VBB Logic Supply Voltage Logic/Reference Input Voltage Range Sense Voltage Notes VSENSE Output Current, Continuous IOUT Package Power Dissipation PD Operating Ambient Temperature TA Maximum Junction Temperature TJ(max) Storage Temperature Range S See graph W –20 to 85 ºC 150 ºC –55 to 150 ºC Value Units 43 ºC/W 67 ºC/W 6 ºC/W Fault conditions that produce excessive junction temperature will activate the device’s thermal shutdown circuitry. These conditions can be tolerated but should be avoided. Tstg Thermal Characteristics Characteristic Symbol Test Conditions* B Package, single-layer PCB, 1 in.2 2-oz. exposed copper Package Thermal Resistance, Junction to Ambient RθJA Package Thermal Resistance, Junction to Tab RθJT LB Package, 2-layer PCB, 0.3 side in.2 2-oz. exposed copper each Note the A3953SB (DIP) and the A3953SLB (SOIC) are electrically identical and share a common terminal number assignment. 16 LOAD SUPPLY 2 15 OUTB RC 3 14 MODE GROUND 4 13 GROUND BRAKE 1 REF VBB LOGIC GROUND 5 LOGIC SUPPLY 6 PHASE 7 ENABLE 8 VCC VBB 12 GROUND 11 SENSE 10 OUTA 9 LOAD SUPPLY ALLOWABLE PACKAGE POWER DISSIPATION (W) *Additional thermal information available on Allegro website. 4 R θJT = 6.0°C/W 3 SUFFIX 'B', R θJA = 43°C/W 2 1 SUFFIX 'LB', R θJA = 67°C/W 0 25 50 75 100 TEMPERATURE IN °C 125 150 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2 A3953 Full-Bridge PWM Motor Driver ELECTRICAL CHARACTERISTICS at TJ = 25°C, VBB = 5 V to 50 V, VCC = 3.0 V to 5.5 V (unless otherwise noted.) Limits Characteristic Symbol Test Conditions Min. Typ. Max. Units VCC — 50 V Power Outputs Load Supply Voltage Range VBB Operating, IOUT = ±1.3 A, L = 3 mH Output Leakage Current ICEX VOUT = VBB — <1.0 50 μA VOUT = 0 V — <-1.0 -50 μA ISO ISENSE - IOUT1, IOUT = 850 mA, VSENSE = 0 V, VCC = 5 V 22 33 38 mA VCE(SAT) VSENSE = 0.4 V, VCC = 3.0 V: Sense Current Offset Output Saturation Voltage BRAKE = H Source Driver, IOUT = -0.85 A — 1.0 1.1 V (Forward/Reverse Mode) Source Driver, IOUT = -1.3 A — 1.7 1.9 V Sink Driver, IOUT = 0.85 A — 0.4 0.5 V Sink Driver, IOUT = 1.3 A — 1.1 1.3 V Output Saturation Voltage VCE(SAT) VSENSE = 0.4 V, VCC = 3.0 V: BRAKE = L Sink Driver, IOUT = 0.85 A — 1.0 1.2 V (Brake Mode) Sink Driver, IOUT = 1.3 A — 1.3 1.5 V IF = 0.85 A — 1.2 1.4 V IF = 1.3 A — 1.4 1.6 V Clamp Diode Forward Voltage VF (Sink or Source) Continued next page… TRUTH TABLE BRAKE ENABLE PHASE MODE OUTA OUTB DESCRIPTION H H X H Off Off H H X L Off Off H L H H H L H L H L H L Forward, Slow Current-Decay Mode H L L H L H Reverse, Fast Current-Decay Mode H L L L L H Reverse, Slow Current-Decay Mode L X X H L L Brake, Fast Current-Decay Mode L X X L L L Brake, No Current Control Sleep Mode Standby Forward, Fast Current-Decay Mode X = Irrelevant Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 A3953 Full-Bridge PWM Motor Driver ELECTRICAL CHARACTERISTICS (continued) at TJ = 25°C, VBB = 5 V to 50 V, VCC = 3.0 V to 5.5 V (unless otherwise noted.) Limits Characteristic Symbol Test Conditions Min. Typ. Max. Units CT = 680 pF, RT= 30 kΩ, VCC = 3.3 V 18.3 20.4 22.5 μs Comparator Trip to Source Off, IOUT = 25 mA Comparator Trip to Source Off, IOUT = 1.3 A — 1.0 1.5 μs — 1.8 2.6 μs IRC Charge On to Source On, IOUT = 25 mA IRC Charge On to Source On, IOUT = 1.3 A — 0.4 0.7 μs — 0.55 0.85 μs VCC = 3.3 V, RT ≥ 12 kΩ, CT = 680 pF 0.8 1.4 1.9 μs VCC = 5.0 V, RT ≥ 12 kΩ, CT = 470 pF 0.8 1.6 2.0 μs ENABLE On to Source On — 1.0 — μs ENABLE Off to Source Off — 1.0 — μs ENABLE On to Sink On — 1.0 — μs ENABLE Off to Sink Off (MODE = L) — 0.8 — μs PHASE Change to Sink On — 2.4 — μs PHASE Change to Sink Off — 0.8 — μs PHASE Change to Source On — 2.0 — μs PHASE Change to Source Off — 1.7 — μs 1 kΩ Load to 25 V, VBB = 50 V 0.3 1.5 3.0 μs IOUT = 1.3 A 70 — — kHz AC Timing PWM RC Fixed Off-time PWM Turn-Off Time PWM Turn-On Time PWM Minimum On Time Propagation Delay Times Crossover Dead Time Maximum PWM Frequency tOFF RC tPWM(OFF) tPWM(ON) tON(min) tpd tCODT fPWM(max) IOUT = ±1.3 A, 50% to 90%: Continued next page… Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 A3953 Full-Bridge PWM Motor Driver ELECTRICAL CHARACTERISTICS (continued) at TJ = 25°C, VBB = 5 V to 50 V, VCC = 3.0 V to 5.5 V (unless otherwise noted. ) Limits Characteristic Symbol Test Conditions Min. Typ. Max. Units TJ — 165 — °C ∆TJ — 8.0 — °C UVLO Enable Threshold 2.5 2.75 3.0 V UVLO Hysteresis 0.12 0.17 0.25 V Control Circuitry Thermal Shutdown Temp. Thermal Shutdown Hysteresis Logic Supply Current ICC(ON) VENABLE = 0.8 V, VBRAKE = 2.0 V — 42 50 mA ICC(OFF) VENABLE = 2.0 V, VMODE = 0.8 V — 12 15 mA ICC(Brake) VBRAKE = 0.8 V — 42 50 mA ICC(Sleep) VENABLE = VMODE = VBRAKE = 2.0 V — 500 800 μA Motor Supply Current IBB(ON) VENABLE = 0.8 V — 2.5 4.0 mA (No Load) IBB(OFF) VENABLE = 2.0 V, VMODE = 0.8 V — 1.0 50 μA IBB(Brake) VBRAKE = 0.8 V — 1.0 50 μA IBB(Sleep) VENABLE = VMODE = 2.0 V — 1.0 50 μA Operating 3.0 5.0 5.5 V Logic Supply Voltage Range VCC Logic Input Voltage VIN(1) 2.0 — — V VIN(0) — — 0.8 V Logic Input Current VSENSE Voltage Range IIN(1) VIN = 2.0 V — <1.0 20 μA IIN(0) VIN = 0.8 V — <-2.0 -200 μA VSENSE(3.3) VCC = 3.0 V to 3.6 V 0 — 0.4 V VSENSE(5.0) VCC = 4.5 V to 5.5 V 0 — 1.0 V Reference Input Current IREF VREF = 0 V to 1 V — — ±5.0 μA Comparator Input Offset Volt. VIO VREF = 0 V — ±2.0 ±5.0 mV Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 A3953 Full-Bridge PWM Motor Driver FUNCTIONAL DESCRIPTION Internal PWM Current Control During Forward and Reverse Operation. The A3953 contains a fixed off-time pulse width modulated (PWM) current-control circuit that can be used to limit the load current to a desired value. The peak value of the current limiting (ITRIP) is set by the selection of an external current sensing resistor (RS) and reference input voltage (VREF). The internal circuitry compares the voltage across the external sense resistor to the voltage on the reference input terminal (REF) resulting in a transconductance function approximated by: VREF ITRIP ≈ – ISO RS The user selects an external resistor (RT) and capacitor (CT) to determine the time period (tOFF = RT x CT) during which the drivers remain disabled (see RC Fixed Off-Time section, below). At the end of the RC interval, the drivers are enabled allowing the load current to increase again. The PWM cycle repeats, maintaining the peak load current at the desired value (figure 2). Figure 2 Fast and Slow Current-Decay Waveforms ENABLE MODE where ISO is the offset due to base drive current. In forward or reverse mode the current-control circuitry limits the load current as follows: when the load current reaches ITRIP, the comparator resets a latch that turns off the selected source driver or selected sink and source driver pair depending on whether the device is operating in slow or fast current-decay mode, respectively. In slow current-decay mode, the selected source driver is disabled; the load inductance causes the current to recirculate through the sink driver and ground clamp diode. In fast currentdecay mode, the selected sink and source driver pair are disabled; the load inductance causes the current to flow from ground to the load supply via the ground clamp and flyback diodes. Figure 1 — Load-Current Paths V BB DRIVE CURRENT RECIRCULATION (SLOW-DECAY MODE) RECIRCULATION (FAST-DECAY MODE) RS I TRIP RC LOAD CURRENT RC Dwg. WP-015-1 INTERNAL PWM CURRENT CONTROL DURING BRAKE-MODE OPERATION Brake Operation - MODE Input High. The brake circuit turns off both source drivers and turns on both sink drivers. For dc motor applications, this has the effect of shorting the motor back-EMF voltage resulting in current flow that dynamically brakes the motor. If the back-EMF voltage is large, and there is no PWM current limiting, the load current can increase to a value that approaches that of a locked rotor condition. To limit the current, when the ITRIP level is reached, the PWM circuit disables the conducting sink drivers. The energy stored in the motor inductance is discharged into the load supply causing the motor current to decay. As in the case of forward/reverse operation, the drivers are enabled after a time given by tOFF = RT x CT (see RC Fixed Off-Time section, below). Depending on the back-EMF voltage (proportional to the motor decreasing speed), the load current again may increase to ITRIP. If so, the PWM cycle will repeat, limiting the peak load current to the desired value. Dwg. EP-006-13A Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 A3953 Full-Bridge PWM Motor Driver During braking, when the MODE input is high, the peak current limit can be approximated by: ITRIP BRAKE MH ≈ VREF RS CAUTION: Because the kinetic energy stored in the motor and load inertia is being converted into current, which charges the VBB supply bulk capacitance (power supply output and decoupling capacitance), care must be taken to ensure the capacitance is sufficient to absorb the energy without exceeding the voltage rating of any devices connected to the motor supply. Brake Operation - MODE Input Low. During braking, with the MODE input low, the internal current-control circuitry is disabled. Therefore, care should be taken to ensure that the motor’s current does not exceed the ratings of the device. The braking current can be measured by using an oscilloscope with a current probe connected to one of the motor’s leads, or if the back-EMF voltage of the motor is known, approximated by: VBEMF – 1V IPEAK BRAKE ML ≈ RLOAD RC Fixed Off-Time. The internal PWM current-control circuitry uses a one shot to control the time the driver(s) remain(s) off. The one-shot time, tOFF (fixed off-time), is determined by the selection of an external resistor (RT) and capacitor (CT) connected in parallel from the RC timing terminal to ground. The fixed off-time, over a range of values of CT = 470 pF to 1500 pF and RT = 12 kΩ to 100 kΩ, is approximated by: tOFF ≈ RT x CT The operation of the circuit is as follows: when the PWM latch is reset by the current comparator, the voltage on the RC terminal will begin to decay from approximately 0.60VCC. When the voltage on the RC terminal reaches approximately 0.22VCC, the PWM latch is set, thereby enabling the driver(s). RC Blanking. In addition to determining the fixed off-time of the PWM control circuit, the CT component sets the comparator blanking time. This function blanks the output of the comparator when the outputs are switched by the internal current-control circuitry (or by the PHASE, BRAKE, or ENABLE inputs). The comparator output is blanked to prevent false over-current detections due to reverse recovery currents of the clamp diodes, and/or switching transients related to distributed capacitance in the load. During internal PWM operation, at the end of the tOFF time, the comparator’s output is blanked and CT begins to be charged from approximately 0.22VCC by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 0.60VCC. When a transition of the PHASE input occurs, CT is discharged to near ground during the crossover delay time (the crossover delay time is present to prevent simultaneous conduction of the source and sink drivers). After the crossover delay, CT is charged by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 0.60VCC. When the device is disabled, via the ENABLE input, CT is discharged to near ground. When the device is re-enabled, CT is charged by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 0.60VCC. For 3.3 V operation, the minimum recommended value for CT is 680 pF ± 5 %. For 5.0 V operation, the minimum recommended value for CT is 470 pF ± 5%. These values ensure that the blanking time is sufficient to avoid false trips of the comparator under normal operating conditions. For optimal regulation of the load current, the above values for CT are recommended and the value of RT can be sized to determine tOFF. For more information regarding load current regulation, see below. LOAD CURRENT REGULATION WITH INTERNAL PWM CURRENT-CONTROL CIRCUITRY When the device is operating in slow current-decay mode, there is a limit to the lowest level that the PWM currentcontrol circuitry can regulate load current. The limitation is the minimum duty cycle, which is a function of the user-selected Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 where tOFF = RT x CT, RLOAD is the series resistance of the load, VBB is the motor supply voltage and t ON(min)max is specified in the Electrical Characteristics table. When the motor is rotating, the back EMF generated will influence the above relationship. For brush dc motor applications, the current regulation is improved. For stepper motor applications, when the motor is rotating, the effect is more complex. A discussion of this subject is included in the section on stepper motors below. The following procedure can be used to evaluate the worst-case slow current-decay internal PWM load current regulation in the system: 1. Set VREF to 0 volts. With the load connected and the PWM current control operating in slow current-decay mode, use an oscilloscope to measure the time the output is low (sink on) for the output that is chopping. This is the typical minimum on time (tON(min) typ) for the device. 2. The CT then should be increased until the measured value of tON(min) is equal to tON(min) max as specified in the electrical characteristics table. 3. When the new value of CT has been set, the value of RT should be decreased so the value for tOFF = RT x CT (with the artificially increased value of CT) is equal to the nominal design value. diodes conduct after the drivers are disabled, resulting in fast current decay. When the device is enabled the internal currentcontrol circuitry will be active and can be used to limit the load current in a slow current-decay mode. For applications that PWM the ENABLE input and desire the internal current-limiting circuit to function in the fast decay mode, the ENABLE input signal should be inverted and connected to the MODE input. This prevents the device from being switched into sleep mode when the ENABLE input is low. Phase PWM. Toggling the PHASE terminal selects which sink/source pair is enabled, producing a load current that varies with the duty cycle and remains continuous at all times. This can have added benefits in bidirectional brush dc servo motor applications as the transfer function between the duty cycle on the PHASE input and the average voltage applied to the motor is more linear than in the case of ENABLE PWM control (which produces a discontinuous current at low current levels). For more information see DC Motor Applications section, below. Synchronous Fixed-Frequency PWM. The internal PWM current-control circuitry of multiple A3953 devices can be synchronized by using the simple circuit shown in figure 3. A 555 IC can be used to generate the reset pulse/blanking signal (t1) for the device and the period of the PWM cycle (t2). The value of t1 should be a minimum of 1.5 ms. When used in this configuration, the RT and CT components should be omitted. The PHASE and ENABLE inputs should not be PWM with this circuit configuration due to the absence of a blanking function synchronous with their transitions. Figure 3 Synchronous Fixed-Frequency Control Circuit V CC 4. The worst-case load-current regulation then can be measured in the system under operating conditions. PWM of the PHASE and ENABLE Inputs. The PHASE and ENABLE inputs can be pulse-width modulated to regulate load current. Typical propagation delays from the PHASE and ENABLE inputs to transitions of the power outputs are specified in the electrical characteristics table. If the internal PWM current control is used, the comparator blanking function is active during phase and enable transitions. This eliminates false tripping of the over-current comparator caused by switching transients (see RC Blanking section, above). Enable PWM. With the MODE input low, toggling the ENABLE input turns on and off the selected source and sink drivers. The corresponding pair of flyback and ground-clamp t 2 100 kΩ value of tOFF and the minimum on-time pulse tON(min) max that occurs each time the PWM latch is reset. If the motor is not rotating (as in the case of a stepper motor in hold/detent mode, a brush dc motor when stalled, or at startup), the worst case value of current regulation can be approximated by: [(VBB – VSAT(source+sink)) x tON(min)max] – (1.05(VSAT(sink) + VF) x tOFF) IAVE ≈ 1.05 x (tON(min)max + tOFF) x RLOAD Full-Bridge PWM Motor Driver 20 kΩ A3953 RC 1 1N4001 2N2222 t RC N 1 Dwg. EP-060 Miscellaneous Information. A logic high applied to both the ENABLE and MODE terminals puts the device into a sleep mode to minimize current consumption when not in use. An internally generated dead time prevents crossover currents that can occur when switching phase or braking. Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8 A3953 Thermal protection circuitry turns off all drivers should the junction temperature reach 165°C (typical). This is intended only to protect the device from failures due to excessive junction temperatures and should not imply that output short circuits are permitted. The hysteresis of the thermal shutdown circuit is approximately 15°C. Full-Bridge PWM Motor Driver for the given level of ILOAD. The value for RθJT is given in the package thermal resistance table for the appropriate package. The power dissipation of the batwing packages can be improved by 20% to 30% by adding a section of printed circuit board copper (typically 6 to 18 square centimeters) connected to the batwing terminals of the device. APPLICATION NOTES The thermal performance in applications that run at high load currents and/or high duty cycles can be improved by adding Current Sensing. The actual peak load current (IPEAK) will be external diodes in parallel with the internal diodes. In internal above the calculated value of ITRIP due to delays in the turn off of PWM slow-decay applications, only the two ground clamp diodes the drivers. The amount of overshoot can be approximated by: need be added. For internal fast-decay PWM, or external PHASE (VBB – [(ITRIP x RLOAD) + VBEMF]) x tPWM(OFF) or ENABLE input PWM applications, all four external diodes IOS ≈ should be added for maximum junction temperature reduction. LLOAD PCB Layout. The load supply terminal, VBB, should where VBB is the motor supply voltage, VBEMF is the back-EMF be decoupled with an electrolytic capacitor (>47 μF is voltage of the load, RLOAD and LLOAD are the resistance and recommended) placed as close to the device as is physically inductance of the load respectively, and tPWM(OFF) is specified in practical. To minimize the effect of system ground I x R drops on the electrical characteristics table. the logic and reference input signals, the system ground should have a low-resistance return to the motor supply voltage. See also The reference terminal has a maximum input bias current of ±5 the Current Sensing and Thermal Considerations sections, above. μA. This current should be taken into account when determining the impedance of the external circuit that sets the reference Fixed Off-Time Selection. With increasing values of tOFF, voltage value. switching losses will decrease, low-level load-current regulation To minimize current-sensing inaccuracies caused by ground trace will improve, EMI will be reduced, the PWM frequency will decrease, and ripple current will increase. The value of tOFF can I x R drops, the current-sensing resistor should have a separate be chosen for optimization of these parameters. For applications return to the ground terminal of the device. For low-value sense where audible noise is a concern, typical values of tOFF are chosen resistors, the I x R drops in the printed wiring board can be significant and should be taken into account. The use of sockets to be in the range of 15 ms to 35 ms. should be avoided as their contact resistance can cause variations Stepper Motor Applications. The MODE terminal in the effective value of RS. can be used to optimize the performance of the device in Generally, larger values of RS reduce the aforementioned effects microstepping/sinusoidal stepper-motor drive applications. When but can result in excessive heating and power loss in the sense the load current is increasing, slow decay mode is used to limit resistor. The selected value of RS should not cause the absolute the switching losses in the device and iron losses in the motor. maximum voltage rating of 1.0 V (0.4 V for VCC = 3.3 V This also improves the maximum rate at which the load current operation), for the SENSE terminal, to be exceeded. can increase (as compared to fast decay) due to the slow rate of decay during tOFF. When the load current is decreasing, fast-decay The current-sensing comparator functions down to ground mode is used to regulate the load current to the desired level. This allowing the device to be used in microstepping, sinusoidal, and prevents tailing of the current profile caused by the back-EMF other varying current-profile applications. voltage of the stepper motor. Thermal Considerations. For reliable operation it is In stepper-motor applications applying a constant current to recommended that the maximum junction temperature be kept below 110°C to 125°C. The junction temperature can be measured the load, slow-decay mode PWM is typically used to limit the best by attaching a thermocouple to the power tab/batwing of the switching losses in the device and iron losses in the motor. device and measuring the tab temperature, TTAB. The junction DC Motor Applications. In closed-loop systems, the temperature can then be approximated by using the formula: speed of a dc motor can be controlled by PWM of the PHASE or ENABLE inputs, or by varying the reference input voltage TJ ≈ TTAB + (ILOAD x 2 x VF x RJT) (REF). In digital systems (microprocessor controlled), PWM of where VF may be chosen from the electrical specification table the PHASE or ENABLE input is used typically thus avoiding Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 9 A3953 Full-Bridge PWM Motor Driver the need to generate a variable analog voltage reference. In this case, a dc voltage on the REF input is used typically to limit the maximum load current. load current will regulate to a value given by: In dc servo applications, which require accurate positioning at low or zero speed, PWM of the PHASE input is selected typically. This simplifies the servo control loop because the transfer function between the duty cycle on the PHASE input and the average voltage applied to the motor is more linear than in the case of ENABLE PWM control (which produces a discontinuous current at low current levels). CAUTION: In fast current-decay mode, when the direction of With bidirectional dc servo motors, the PHASE terminal can be used for mechanical direction control. Similar to when braking the motor dynamically, abrupt changes in the direction of a rotating motor produces a current generated by the back-EMF. The current generated will depend on the mode of operation. If the internal current control circuitry is not being used, then the maximum load current generated can be approximated by ILOAD = (VBEMF + VBB)/RLOAD where VBEMF is proportional to the motor’s speed. If the internal slow current-decay control circuitry is used, then the maximum load current generated can be approximated by ILOAD = VBEMF/RLOAD. For both cases care must be taken to ensure that the maximum ratings of the device are not exceeded. If the internal fast current-decay control circuitry is used, then the ILOAD = VREF/RS. the motor is changed abruptly, the kinetic energy stored in the motor and load inertia will be converted into current that charges the VBB supply bulk capacitance (power supply output and decoupling capacitance). Care must be taken to ensure that the capacitance is sufficient to absorb the energy without exceeding the voltage rating of any devices connected to the motor supply. See also the Brake Operation section, above. Soldering Considerations. The lead (Pb) free (100% matte tin) plating on lead terminations is 100% backwardcompatible for use with traditional tin-lead solders of any composition, at any temperature of soldering that has been traditionally used for that tin-lead solder alloy. Further, 100% matte tin finishes solder well with tin-lead solders even at temperatures below 232°C. This is because the matte tin dissolves easily in the tin-lead. Additional information on soldering is available on the Allegro Web site, www.allegromicro.com. Figure 4 — Typical Application Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 10 A3953 Full-Bridge PWM Motor Driver B package 16-pin DIP 19.05±0.25 16 +0.10 0.38 –0.05 +0.76 6.35 –0.25 +0.38 10.92 –0.25 7.62 A 1 2 5.33 MAX +0.51 3.30 –0.38 1.27 MIN +0.25 1.52 –0.38 2.54 For Reference Only (reference JEDEC MS-001 BB) Dimensions in millimeters Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area 0.46 ±0.12 LB package 16-pin SOICW 10.30±0.20 4° ±4 16 1.27 0.65 +0.07 0.27 –0.06 10.30±0.33 7.50±0.10 A 9.50 +0.44 0.84 –0.43 2.25 1 2 0.25 16X SEATING PLANE 0.10 C 0.41 ±0.10 1.27 2.65 MAX 0.20 ±0.10 C SEATING PLANE GAUGE PLANE B PCB Layout Reference View For Reference Only Pins 4 and 5, and 12 and 13 internally fused Dimensions in millimeters (reference JEDEC MS-013 AA) Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area B Reference pad layout (reference IPC SOIC127P1030X265-16M) All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and PCB layout tolerances Copyright ©1995-2008, Allegro MicroSystems, Inc. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. For the latest version of this document, visit our website: www.allegromicro.com Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 11