A4950 Full-Bridge DMOS PWM Motor Driver Description Features and Benefits • Low RDS(on) outputs • Overcurrent protection (OCP) ▫ Motor short protection ▫ Motor lead short to ground protection ▫ Motor lead short to battery protection • Low Power Standby mode • Adjustable PWM current limit • Synchronous rectification • Internal undervoltage lockout (UVLO) • Crossover-current protection • A4950K is AEC-Q100 Grade 1 qualified • Commercial temperature grade (A4950E: –40°C to 85°C ) • Automotive temperature grade (A4950K: –40°C to 125°C) Designed for pulse width modulated (PWM) control of DC motors, the A4950 is capable of peak output currents to ±3.5 A and operating voltages to 40 V. Input terminals are provided for use in controlling the speed and direction of a DC motor with externally applied PWM control signals. Internal synchronous rectification control circuitry is provided to lower power dissipation during PWM operation. Internal circuit protection includes overcurrent protection, motor lead short to ground or supply, thermal shutdown with hysteresis, undervoltage monitoring of VBB, and crossovercurrent protection. For high ambient operating temperature applications, an automotive grade device is offered (A4950K). The K grade device is tested across extended temperature and voltage ranges to ensure compliance in automotive or industrial applications. Package: 8-pin SOICN with exposed thermal pad (suffix LJ) The A4950 is provided in a low-profile 8-pin SOICN package with exposed thermal pad (suffix LJ) that is lead (Pb) free, with 100% matte tin leadframe plating. Not to scale Functional Block Diagram Load Supply OSC IN1 Charge Pump VBB Control Logic Disable IN2 TSD UVLO OUT1 OUT2 7V GND LSS VREF A4950-DS, Rev. 4 ÷ 10 (Optional) A4950 Full-Bridge DMOS PWM Motor Driver Selection Guide Part Number Packing A4950ELJTR-T A4950KLJTR-T Ambient Operating Temperature, TA 3000 pieces per 13-in. reel 3000 pieces per 13-in. reel –40°C to 85°C –40°C to 125°C Absolute Maximum Ratings Characteristic Rating Unit VBB 40 V Logic Input Voltage Range VIN –0.3 to 6 V VREF Input Voltage Range VREF –0.3 to 6 V Load Supply Voltage Sense Voltage (LSS pin) Symbol Notes VS –0.5 to 0.5 V Motor Outputs Voltage VOUT –2 to 42 V Output Current IOUT Duty cycle = 100% 3.5 A Transient Output Current iOUT TW < 500 ns Operating Temperature Range Maximum Junction Temperature Storage Temperature Range TA 6 A Temperature Range E –40 to 85 °C Temperature Range K –40 to 125 °C TJ(max) 150 °C Tstg –55 to 150 °C Thermal Characteristics may require derating at maximum conditions, see application information Characteristic Package Thermal Resistance Symbol RθJA Value Unit On 2-layer PCB with 0.8 in2. exposed 2-oz. copper each side Test Conditions* 62 ºC/W On 4-layer PCB based on JEDEC standard 35 ºC/W *Additional thermal information available on the Allegro website. Terminal List Table Pin-out Diagram GND 1 IN2 2 IN1 3 VREF 4 PAD Number Name 1 GND Function 2 IN2 Logic input 2 Ground 8 OUT2 3 IN1 Logic input 1 7 LSS 4 VREF Analog input 5 VBB 6 OUT1 7 LSS 8 OUT2 – PAD 6 OUT1 5 VBB Load supply voltage DMOS full bridge output 1 Power return – sense resistor connection DMOS full bridge output 2 Exposed pad for enhanced thermal dissipation Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2 A4950 Full-Bridge DMOS PWM Motor Driver ELECTRICAL CHARACTERISTICS Valid for Temperature Range E version at TJ = 25°C and for Temperature Range K version at TJ = –40°C to 150°C, VBB = 8 to 40 V, unless otherwise specified Characteristic Symbol Test Conditions Min. Typ. Max. Unit General Load Supply Voltage Range VBB RDS(on) Sink + Source Total RDS(on) Load Supply Current IBB Body Diode Forward Voltage Vf 8 – 40 V IOUT = |2.5 A|, TJ = 25°C – 0.6 0.8 Ω IOUT = |2.5 A|, TJ = 150°C – 1.1 1.5 Ω fPWM < 30 kHz – 10 20 mA Low Power Standby mode – – 10 μA Source diode, If = –2.5 A – – 1.5 V Sink diode, If = 2.5 A – – 1.5 V Logic Inputs Logic Input Voltage Range VIN(1) 2.0 – – V VIN(0) – – 0.8 V – – 0.4 V VIN(STANDBY) Low Power Standby mode Logic Input Current Logic Input Pull-Down Resistance IIN(1) VIN = 2.0 V – 40 100 μA IIN(0) VIN = 0.8 V – 16 40 μA – 50 – kΩ VHYS – 250 550 mV Crossover Delay tCOD 50 – 500 ns VREF Input Voltage Range VREF Input Hysteresis RR RLOGIC(PD) VIN = 0 V = IN1 = IN2 Timing Current Gain Blank Time AV 0 – 5 V VREF / ISS , VREF = 5 V 9.5 – 10.5 V/V VREF / ISS , VREF = 2.5 V 9.0 – 10.0 V/V VREF / ISS , VREF = 1 V 8.0 – 10.0 V/V 2 3 4 μs 16 25 34 μs – 1 1.5 ms – – 30 μs 7 7.5 7.95 V – 500 – mV Temperature increasing – 160 – °C Recovery = TJTSD – TTSDhys – 15 – °C tBLANK Constant Off-time toff Standby Timer tst Power-Up Delay tpu IN1 = IN2 < VIN(STANDBY) Protection Circuits UVLO Enable Threshold UVLO Hysteresis Thermal Shutdown Temperature Thermal Shutdown Hysteresis VBBUVLO VBB increasing VBBUVLOhys TJTSD TTSDhys Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 A4950 Full-Bridge DMOS PWM Motor Driver Characteristic Performance PWM Control Timing Diagram VIN(1) IN1 GND VIN(1) IN2 GND +IREG IOUT(x) 0A -IREG Forward/ Fast Decay Reverse/ Fast Decay Forward/ Slow Decay Reverse/ Slow Decay PWM Control Truth Table IN1 IN2 10×VS > VREF OUT1 OUT2 0 1 False L H Reverse Function 1 0 False H L Forward 0 1 True H/L L Chop (mixed decay), reverse 1 0 True L H/L 1 1 False L L Brake (slow decay) 0 0 False Z Z Coast, enters Low Power Standby mode after 1 ms Chop (mixed decay), forward Note: Z indicates high impedance. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 A4950 Full-Bridge DMOS PWM Motor Driver Functional Description Device Operation The A4950 is designed to operate DC motors. The output drivers are all low-RDS(on) , N-channel DMOS drivers that feature internal synchronous rectification to reduce power dissipation. The current in the output full bridge is regulated with fixed off-time pulse width modulated (PWM) control circuitry. The IN1 and IN2 inputs allow two-wire control for the bridge. Protection circuitry includes internal thermal shutdown, and protection against shorted loads, or against output shorts to ground or supply. Undervoltage lockout prevents damage by keeping the outputs off until the driver has enough voltage to operate normally. Standby Mode Low Power Standby mode is activated when both input (INx) pins are low for longer than 1 ms. Low Power Standby mode disables most of the internal circuitry, including the charge pump and the regulator. When the A4950 is coming out of standby mode, the charge pump should be allowed to reach its regulated voltage (a maximum delay of 200 μs) before any PWM commands are issued to the device. Internal PWM Current Control Initially, a diagonal pair of source and sink FET outputs are enabled and current flows through the motor winding and the optional external current sense resistor, RS . When the voltage across RS equals the comparator trip value, then the current sense comparator resets the PWM latch. The latch then turns off the sink and source FETs (Mixed Decay mode). VREF The maximum value of current limiting is set by the selection of RSx and the voltage at the VREF pin. The transconductance function is approximated by the maximum value of current limiting, ITripMAX (A), which is set by: ITripMAX = VREF 10 RS where VREF is the input voltage on the VREF pin (V) and RS is the resistance of the sense resistor (Ω) on the LSS terminal. Overcurrent Protection A current monitor will protect the IC from damage due to output shorts. If a short is detected, the IC will latch the fault and disable the outputs. The fault latch can only be cleared by coming out of Low Power Standby mode or by cycling the power to VBB. During OCP events, Absolute Maximum Ratings may be exceeded for a short period of time before the device latches. Shutdown If the die temperature increases to approximately 160°C, the full bridge outputs will be disabled until the internal temperature falls below a hysteresis, TTSDhys , of 15°C. Internal UVLO is present on VBB to prevent the output drivers from turning-on below the UVLO threshold. Braking The braking function is implemented by driving the device in Slow Decay mode, which is done by applying a logic high to both inputs, after a bridge-enable Chop command (see PWM Control Truth Table). Because it is possible to drive current in both directions through the DMOS switches, this configuration effectively shorts-out the motor-generated BEMF, as long as the Chop command is asserted. The maximum current can be approximated by VBEMF / RL . Care should be taken to ensure that the maximum ratings of the device are not exceeded in worse case braking situations: high speed and high-inertia loads. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 A4950 Full-Bridge DMOS PWM Motor Driver Synchronous Rectification When a PWM off-cycle is triggered by an internal fixed off-time cycle, load current will recirculate. The A4950 synchronous rectification feature turns-on the appropriate DMOSFETs during the current decay, and effectively shorts out the body diodes with the low RDS(on) driver. This significantly lowers power dissipation. When a zero current level is detected, synchronous rectification is turned off to prevent reversal of the load current. Mixed Decay Operation The bridges operate in Mixed Decay mode. Referring to the lower panel of the figure below, as the trip point is reached, the device goes into fast decay mode for 50% of the fixed off-time period. After this fast decay portion the device switches to slow decay mode for the remainder of the off-time. During transitions from fast decay to slow decay, the drivers are forced off for the Crossover Delay, tCOD . This feature is added to prevent shootthrough in the bridge. During this “dead time” portion, synchronous rectification is not active, and the device operates in fast decay and slow decay only. Mixed Decay Mode Operation VPHASE + IOUT See Enlargement A 0 – Enlargement A Fixed Off-Time, toff = 25 μs 0.50 × toff 0.50 × toff ITrip IOUT Fast Decay tCOD tCOD Slow Decay tCOD Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 A4950 Full-Bridge DMOS PWM Motor Driver Application Information Sense Pin (LSS) In order to use PWM current control, a low-value resistor is placed between the LSS pin and ground for current sensing purposes. To minimize ground-trace IR drops in sensing the output current level, the current sensing resistor should have an independent ground return to the star ground point. This trace should be as short as possible. For low-value sense resistors, the IR drops in the PCB can be significant, and should be taken into account. of the device makes a good location for the star ground point. The exposed pad can be connected to ground for this purpose. When selecting a value for the sense resistor be sure not to exceed the maximum voltage on the LSS pin of ±500 mV at maximum load. During overcurrent events, this rating may be exceeded for short durations. Layout The PCB should have a thick ground plane. For optimum electrical and thermal performance, the A4950 must be soldered directly onto the board. On the underside of the A4950 package is an exposed pad, which provides a path for enhanced thermal dissipation. The thermal pad must be soldered directly to an exposed surface on the PCB in order to achieve optimal thermal conduction. Thermal vias are used to transfer heat to other layers of the PCB. Ground A star ground should be located as close to the A4950 as possible. The copper ground plane directly under the exposed thermal pad The load supply pin, VBB, should be decoupled with an electrolytic capacitor (typically 100 μF) in parallel with a lower valued ceramic capacitor placed as close as practicable to the device. GND Solder A4950 GND Trace (2 oz.) Signal (1 oz.) Ground (1 oz.) PCB Thermal (2 oz.) OUT2 Thermal Vias RS OUT1 C1 A4950 C2 BULK CAPACITANCE 1 GND VBB IN2 IN1 VREF OUT2 PAD LSS RS OUT1 VBB VBB C1 GND C2 GND Bill of Materials Item Reference Value Units Description 1 RS 0.25 (for VREF = 5 V, IOUT = 2 A) Ω 2512, 1 W, 1% or better, carbon film chip resistor 2 C1 0.22 μF X5R minimum, 50 V or greater 3 C2 100 μF Electrolytic, 50 V or greater Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 A4950 Full-Bridge DMOS PWM Motor Driver Package LJ, 8-Pin SOICN with exposed thermal pad 4.90 ±0.10 0.65 8° 0° 8 B A 1 3.90 ±0.10 6.00 ±0.20 2 SEATING PLANE GAUGE PLANE Branded Face SEATING PLANE 0.10 C 1.27 BSC 1 1.27 0.40 0.25 BSC 0.51 0.31 2.41 1.04 REF 3.30 NOM 8X C 5.60 2 3.30 C PCB Layout Reference View For Reference Only; not for tooling use (reference MS-012BA) Dimensions in millimeters Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown 1.70 MAX 0.15 0.00 1.27 1.75 0.25 0.17 2.41 NOM 8 A Terminal #1 mark area B Exposed thermal pad (bottom surface); dimensions may vary with device C Reference land pattern layout (reference IPC7351 SOIC127P600X175-9AM); all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and PCB layout tolerances; when mounting on a multilayer PCB, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5) Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8 A4950 Full-Bridge DMOS PWM Motor Driver Revision History Revision Revision Date Rev. 4 August 6, 2012 Description of Revision Add AEC qualification; update PWM table Copyright ©2011-2013, Allegro MicroSystems, LLC Allegro MicroSystems, LLC 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, LLC 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, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 9