A4941 Three-Phase Sensorless Fan Driver Features and Benefits Description • Sensorless (no Hall sensors required) • Soft switching for reduced audible noise • Minimal external components • PWM speed input • FG speed output • Low power standby mode • Lock detection • Optional overcurrent protection • Variant A automotive qualified to AEC-Q100 Grade 2 The A4941 three-phase motor driver incorporates BEMF sensing to eliminate the requirement for Hall sensors in fan applications. A pulse wave modulated (PWM) input is provided to control motor speed, allowing system cost savings by eliminating external variable power supply. PWM input can also be used as an on/off switch to disable motor operation and place the IC into a low power standby mode. The A4941 is provided in a 16-pin TSSOP package (suffix LP) with an exposed thermal pad. It is lead (Pb) free, with 100% matte tin leadframe plating. Package: 16-pin TSSOP with exposed thermal pad (suffix LP) Not to scale Functional Block Diagram 12 V 0.1 μF VCP 0.1 μF CP1 VBB CP2 Charge Pump 10 μF +VINT OUTA SLEW Soft Switch PWM Control Logic 3-Phase Half Bridges OUTB M OUTC 25 kHz OSC SENSE OCP Timers VBB 0.167 Ω TEST Sequencer (Direction) Startup OSC CTAP CDCOM Adaptive Commutation Delay + FG FCOM + – BEMF Comparator A4941-DS, Rev. 4 OUTA OUTB – 10 kΩ GND – FC + O/C OUTC GND A4941 Three-Phase Sensorless Fan Driver Selection Guide Part Number Application A4941GLPTR-T A4941GLPTR-A-T Packing Commerical/Industrial Automotive 4000 pieces per 13-in. reel 4000 pieces per 13-in. reel Absolute Maximum Ratings Characteristic Symbol Supply Voltage VBB Logic Input Voltage Range VIN Logic Output Voltage VOUT Output Current IOUT Notes Rating Unit 20 V PWM, SLEW –0.3 to 5.5 V FC –0.3 to VBB V FG VBB V Peak (startup and lock rotor) 1.25 A r m s , duty cycle = 100% 900 mA Operating Ambient Temperature TA –40 to 105 ºC Maximum Junction Temperature TJ(max) 150 ºC Tstg –55 to 150 ºC Storage Temperature G temperature range Recommended Operating Conditions Characteristic Symbol Supply Voltage Conditions Min. VBB Output Current IOUT Typ. Max. Unit 5 – 16 V Peak (startup and lock rotor) – – 1 A Run current – <500 – mA Value Unit On 4-layer PCB based on JEDEC standard 34 ºC/W On 2-layer PCB with 1 in.2 of copper area each side 52 ºC/W Thermal Characteristics may require derating at maximum conditions Characteristic Symbol RθJA Package Thermal Resistance Test Conditions* *Additional thermal information available on the Allegro website Terminal List Table Pin-out Diagram OUTC 1 16 OUTB CP1 2 15 OUTA CP2 3 14 SENSE VCP 4 GND 5 SLEW 6 PWM 7 FG 8 PAD 13 VBB Name Number Function CP1 2 Charge pump CP2 3 Charge pump CTAP 12 Motor terminal center tap FC 10 Logic input FG 8 GND 5, 11 Speed output signal Ground OUTA 15 Motor terminal A OUTB 16 Motor terminal B 10 FC OUTC 1 Motor terminal C 9 TEST PWM 7 Logic input SENSE 14 Sense resistor connection SLEW 6 Logic input TEST 9 Test use only, leave open circuit VBB 13 Input supply VCP 4 Charge pump 12 CTAP 11 GND Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2 A4941 Three-Phase Sensorless Fan Driver ELECTRICAL CHARACTERISTICS Valid at TJ = –40 to 105°C, VBB = 5 to 16 V*; unless otherwise noted Characteristics VBB Supply Current Symbol Test Conditions IBB IBBST Min. Typ. Max. Unit – 2.5 5 mA Standby mode, PWM = 0 V, SLEW = FC = O/C – 25 50 μA I = 800 mA, TJ = 25°C – 800 1200 mΩ VOCL 180 200 220 mV VIL – – 0.8 V PWM High Level VIH 2 – – V Input Hysteresis VHYS – 300 600 mV Total Driver RDS(on) (Sink + Source) Overcurrent Threshold PWM Low Level Logic Input Current Output Saturation Voltage FG Output Leakage RDS(on) IIN PWM, VIN = 0 V –25 –15 –5 μA SLEW, VIN = 0 V –70 –50 –20 μA FC, VIN = 0 V μA –30 –15 –5 VSAT I = 5 mA – – 0.3 V IFG V = 16 V – – 1 μA 1.6 2 2.4 s Protection Circuitry Lock Protection Thermal Shutdown Temperature ton toff 4 5 6 s 150 165 180 °C 15 – °C 4.3 4.7 V TJTSD Temperature increasing Thermal Shutdown Hysteresis TJHYS Recovery = TJTSD – ∆TJ – VBB Undervoltage Lockout (UVLO) VUVLO VBB rising – *For the A4941GLPTR-T the electrical test is performed at 12 V only and characterized across the voltage range. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 A4941 Three-Phase Sensorless Fan Driver Functional Description The driver system is a three-phase, BEMF sensing motor controller and driver. Commutation is controlled by a proprietary BEMF sensing technique. The motor drive system consists of three half bridge NMOS outputs, BEMF sensing circuits, adaptive commutation control, and state sequencer. The sequencer determines which output devices are active. The BEMF sensing circuits and adaptive commutation circuits determine when the state sequencer advances to the next state. A complete self-contained BEMF sensing commutation scheme is provided. The three half-bridge outputs are controlled by a state machine with six possible states, shown in figure 1. Motor BEMF is sensed at the tri-stated output for each state. BEMF sensing motor commutation relies on the accurate comparison of the voltage on the tri-stated output to the voltage at the center tap of the motor. The BEMF zero crossing, the point where the tri-stated motor winding voltage crosses the center tap voltage, is used as a positional reference. The zero crossing occurs roughly halfway through one commutation cycle. Output State A B C D E Adaptive commutation circuitry and programmable timers determine the optimal commutation points with minimal external components. The major blocks within this system are: the BEMF zero crossing detector, Commutation Delay timer, and the Blank timer. BEMF Zero Cross Detection BEMF zero crossings are detected by comparing the voltage at the tri-stated motor winding to the voltage at the motor center tap. Zero crossings are indicated by the FCOM signal, which goes high at each valid zero crossing and low at the beginning of the next commutation. In each state, the BEMF detector looks for the first correct polarity zero crossing and latches it until the next state. This latching action, along with precise comparator hysteresis, makes for a robust sensing system. At the beginning of each commutation event, the BEMF detectors are inhibited for a period of time set by the Blank timer. This is done so that commutation transients do not disturb the BEMF sensing system. Commutation Event See figure 1 for timing relationships. The commutation sequence is started by a CDCOM pulse or a valid XCOM at startup. After F A B C D E F OUTA OUTB OUTC FCOM CDCOM FG Figure 1. Motor Terminal Output States Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 A4941 Three-Phase Sensorless Fan Driver the commutation delay period, a CDCOM is asserted, starting the Blank timer. The Blank signal disables the BEMF detector so the comparator is not active during the commutation transients. The next zero crossing, detected on the tri-stated output, causes FCOM to go high. This triggers the Commutation Delay timer and the sequence repeats. CTAP Connection pin for motor center-tap if available. If not available (such as with delta type motors), the null point will be generated internally. • PWM also can be used as a control input to start and stop the motor. • For PWM applications, input frequencies in the range 15 to 30 kHz are applied directly to the motor windings. If the PWM duty cycle is very small, then the IC will apply a minimum pulse width of typically 6 μs. This minimum pulse width effects the minimum speed. As a result of having a minimum pulse width, the IC can startup and operate down to very short duty cycles. Startup At startup, commutations are provided by an onboard oscillator. These commutations are part of the startup scheme, to step the motor to generate BEMF until legitimate BEMF zero crossings are detected and normal BEMF sensing commutation is achieved. Until an appropriate number of FCOM pulses are achieved (96), 100% PWM will be applied to the motor windings. SLEW Input Enables or disables soft switching by connection as follows: Standby Mode Driving PWM low for 500 μs causes the IC to enter a low power standby mode. FC Input This is the logic input to set force commutation time at startup, by connection as follows: Lock Detect Valid FCOM signals must be detected to ensure the motor is not stalled. If a valid FG is not detected for 2 s, the outputs will be disabled for 5 s before an auto-restart is attempted. FG Output The FG output provides fan speed information to the system. FG is an open drain output. PWM Input The duty cycle applied to the PWM pin is translated directly to an average duty cycle applied across the motor windings to control speed. • For voltage controlled applications, where VBB controls the speed, PWM can be left open circuit. PWM is internally pulledup to logic high level. SLEW Pin Connection Soft Start Status GND Enabled Open Disabled FC Pin Connection Startup Commutation Time (ms) GND 100 VBB 50 Open 200 Overcurrent Protection If needed, a sense resistor can be installed to limit current. (See Applications Information section for more details.) The current limit trip point would be set by: IOCL = 200 mV / RS . When the trip point is reached, if the threshold voltage, VOCL , is exceeded, the drivers will be disabled for 25 μs. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 A4941 Three-Phase Sensorless Fan Driver Input/Output Structures VBB VCP GND CP1 GND CP2 GND 100 kΩ SLEW 250 kΩ PWM 8V GND GND GND VBB VBB 8V VBB OUTA 25 V CTAP MOS Parasitic OUTB OUTC GND GND GND MOS Parasitic OUTA OUTB OUTC GND VBB FC FG TEST GND 8V GND GND Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 A4941 Three-Phase Sensorless Fan Driver Application Information M Name CTAP VBB C3 VBB R2 C2 1 OUTC 2 CP1 3 CP2 4 VCP 5 GND 6 SLEW 7 PWM 8 FG A4941 PAD OUTB 16 OUTA 15 SENSE 14 VBB 13 R1 D1 C1 CTAP 12 CTAP GND 11 FC 10 TEST 9 Typical Value C1 10 μF / 25 V C2,C3 0.1 μF / 25 V Charge pump ceramic capacitors R2 10 kΩ D1 >1.5 A rated D2 15 V R1 0.167 Ω D2 VBB Typical Application Circuit; speed adjusted via VBB Startup Oscillator Setting (FC) Typically, the 50 ms setting is optimum for motors appropriate for use with the A4941. If the motor does not produce a proper BEMF signal at startup when power is applied, a longer setting may be required. SLEW Setting Connect SLEW to ground to enable the soft switching function. For some motors, soft switching may reduce audible noise. Enabling the soft switching function can result in motor stall for some motors, specifically motors with large inductance that run at higher speeds. For this situation, there are two potential solutions: • Limit the motor speed by lowering the maximum demand, by reducing either Vmotor(max) or the PWM duty applied. • Disable soft switching by leaving SLEW pin open circuit. Current Limiting Use of the current limit circuit is not required. If motor resistance (phase-to-phase) will limit the current below the rating in the Description VBB supply capacitor, minimum 10 μF, electrolytic can be used FG pull-up resistor, can be pulled-up to VBB if required Optional blocking diode for supply reverse polarity protection Transient voltage suppressor (TVS) Current limiting sense resistor, required for low resistance motors Absolute Maximum table, then simply connect the SENSE pin to ground. That is: • If (VBB(max) / Rmotor ) < 1.25 A, eliminate RS. • If (VBB(max) / Rmotor ) > IOUT (max), the choice of RS determines the current limit setting; recommended range is 167 mΩ < RS < 250 mΩ. Note: For some motor types, use of the current limit circuit may prevent proper startup due to the effect of the chopping on the BEMF voltage appearing on the tri-stated winding. Layout Notes • Connect GND pins (5,11) to exposed pad ground area under package. • Add thermal vias from exposed pad to bottom side ground plane. • Place VBB decoupling capacitor as close to the IC as possible. • Place sense resistor, (if used), as close to the IC as possible. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 A4941 Three-Phase Sensorless Fan Driver Package LP, 16-Pin TSSOP with Exposed Thermal Pad 0.45 5.00±0.10 16 0.65 16 8º 0º 0.20 0.09 1.70 B 3 NOM 4.40±0.10 3.00 6.40±0.20 6.10 0.60 ±0.15 A 1 1.00 REF 2 3 NOM 0.25 BSC Branded Face 16X SEATING PLANE 0.10 C 0.30 0.19 C 3.00 C PCB Layout Reference View For Reference Only; not for tooling use (reference MO-153 ABT) Dimensions in millimeters Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown 1.20 MAX 0.65 BSC 1 2 SEATING PLANE GAUGE PLANE 0.15 0.00 A Terminal #1 mark area B Exposed thermal pad (bottom surface); dimensions may vary with device C Reference land pattern layout (reference IPC7351 SOP65P640X110-17M); 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 A4941 Three-Phase Sensorless Fan Driver Revision History Revision Revision Date Rev. 4 December 20, 2012 Description of Revision Add information on CTAP, Automotive variant Copyright ©2010-2013, 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