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Technical content
Description
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. A4941-DS, Rev. 4 Features and Benefits
- 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 Three-Phase Sensorless Fan Driver Package: 16-pin TSSOP with exposed thermal pad (suffix LP) Functional Block Diagram Not to scale A4941 Charge Pump VCP CP1 CP2 OCP 12 V 25 kHz Timers +VINT Control Logic Soft Switch OSC Startup OSC CDCOM FCOM Adaptive Commutation Delay Sequencer (Direction) 0.1 μF 0.1 μF OUTA OUTB M3-Phase Half Bridges OUTC SENSE GND 0.167 Ω 10 kΩ VBB O/C FG FC TEST PWM SLEW VBB 10 μF CTAP GND BEMF Comparator OUTA OUTB OUTC
Three-Phase Sensorless Fan DriverA4941 2Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A. Pin-out Diagram Absolute Maximum Ratings Characteristic Symbol Notes Rating Unit Supply Voltage V BB 20 V Logic Input Voltage Range V IN PWM, SLEW –0.3 to 5.5 V FC –0.3 to V BB V Logic Output Voltage V OUT FG V BB V Output Current I OUT Peak (startup and lock rotor) 1.25 A rms, duty cycle = 100% 900 mA Operating Ambient Temperature T A G temperature range –40 to 105 ºC Maximum Junction Temperature T J(max) 150 ºC Storage Temperature T stg –55 to 150 ºC Terminal List Table Name Number Function CP1 2 Charge pump CP2 3 Charge pump CTAP 12 Motor terminal center tap FC 10 Logic input FG 8 Speed output signal GND 5, 11 Ground OUTA 15 Motor terminal A OUTB 16 Motor terminal B OUTC 1 Motor terminal C 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 Selection Guide Part Number Application Packing A4941GLPTR-T Commerical/Industrial 4000 pieces per 13-in. reel A4941GLPTR-A-T Automotive 4000 pieces per 13-in. reel Thermal Characteristics may require derating at maximum conditions Characteristic Symbol Test Conditions* Value Unit Package Thermal Resistance RθJA 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 *Additional thermal information available on the Allegro website Recommended Operating Conditions Characteristic Symbol Conditions Min. Typ. Max. Unit Supply Voltage V BB 5 – 16 V Output Current I OUT Peak (startup and lock rotor) – – 1 A Run current – <500 – mA OUTC CP1 CP2 VCP GND SLEW PWM FG OUTB OUTA SENSE VBB CTAP GND FC TEST PAD
ELECTRICAL CHARACTERISTICS Valid at TJ = –40 to 105°C, VBB = 5 to 16 V*; unless otherwise noted Characteristics Symbol Test Conditions Min. Typ. Max. Unit VBB Supply Current IBB – 2.5 5 mA IBBST Standby mode, PWM = 0 V, SLEW = FC = O/C – 25 50 μA Total Driver RDS(on) (Sink + Source) R DS(on) I = 800 mA, TJ = 25°C – 800 1200 m Ω Overcurrent Threshold V OCL 180 200 220 mV PWM Low Level V IL – – 0.8 V PWM High Level V IH 2––V Input Hysteresis V HYS – 300 600 mV Logic Input Current I IN PWM, VIN = 0 V –25 –15 –5 μA SLEW, VIN = 0 V –70 –50 –20 μA FC, VIN = 0 V –30 –15 –5 μA Output Saturation Voltage V SAT I = 5 mA – – 0.3 V FG Output Leakage I FG V = 16 V – – 1 μA Protection Circuitry Lock Protection ton 1.6 2 2.4 s toff 456s Thermal Shutdown Temperature T JTSD Temperature increasing 150 165 180 °C Thermal Shutdown Hysteresis T JHYS Recovery = TJTSD – ∆TJ –1 5–° C VBB Undervoltage Lockout (UVLO) V UVLO VBB rising – 4.3 4.7 V *For the A4941GLPTR-T the electrical test is performed at 12 V only and characterized across the voltage range. Three-Phase Sensorless Fan DriverA4941 3Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A.
Worcester, Massachusetts 01615-0036 U.S.A. is sensed at the tri-stated output for each state. roughly halfway through one commutation cycle. mutation transients do not disturb the BEMF sensing system. Figure 1. Motor Terminal Output States
Three-Phase Sensorless Fan DriverA4941 5Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. 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. 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. Standby Mode Driving PWM low for 500 μs causes the IC to enter a low power standby mode. 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 V BB controls the speed, PWM can be left open circuit. PWM is internally pulled- up to logic high level.
- 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 mini- mum 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. SLEW Input Enables or disables soft switching by connection as follows: SLEW Pin Connection Soft Start Status GND Enabled Open Disabled FC Input This is the logic input to set force commutation time at startup, by connection as follows: 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: I OCL = 200 mV / RS . When the trip point is reached, if the threshold voltage, VOCL , is exceeded, the drivers will be disabled for 25 μs.
Three-Phase Sensorless Fan DriverA4941 6Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. Input/Output Structures GND GND 8 V 100 kΩ VBB 25 V GND SLEW VCP GND CP2 GND CP1 VBB GND GND GND 8 V 250 kΩ PWM GND GND
8 VTESTFC
V BB GND
Three-Phase Sensorless Fan DriverA4941 7Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A.
Application Information
M VBB VBB VBB CTAP CTAP Typical Application Circuit; speed adjusted via VBB Name Typical Value Description C1 10 μF / 25 V VBB supply capacitor, minimum 10 μF, electrolytic can be used C2,C3 0.1 μF / 25 V Charge pump ceramic capacitors R2 10 k Ω FG pull-up resistor, can be pulled-up to VBB if required D1 >1.5 A rated Optional blocking diode for supply reverse polarity protection D2 15 V Transient voltage suppressor (TVS) R1 0.167 Ω Current limiting sense resistor, required for low resistance motors 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 func- tion. 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 V motor(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 Absolute Maximum table, then simply connect the SENSE pin to ground. That is:
- If (V BB(max) / Rmotor ) < 1.25 A, eliminate RS.
- If (VBB(max) / Rmotor ) > IOUT (max), the choice of RS deter- mines the current limit setting; recommended range is 167 mΩ < R S < 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 V BB decoupling capacitor as close to the IC as possible.
- Place sense resistor, (if used), as close to the IC as possible.
Three-Phase Sensorless Fan DriverA4941 8Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. Package LP, 16-Pin TSSOP with Exposed Thermal Pad A
1.20 MAX
0.15 0.00 0.30 0.19 0.20 0.09 0.60 ±0.15
1.00 REF
C SEATING PLANEC0.10 16X
0.65 BSC
0.25 BSC
5.00±0.10 GAUGE PLANE SEATING PLANE A Terminal #1 mark area B 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 B C Exposed thermal pad (bottom surface); dimensions may vary with device 6.10 0.65 0.45 1.70 3.00 3.00 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) PCB Layout Reference View C Branded Face
3 NOM
Three-Phase Sensorless Fan DriverA4941 9Allegro MicroSystems, LLC Worcester, Massachusetts 01615-0036 U.S.A. Copyright ©2010-2013, Allegro MicroSystems, LLC Allegro MicroSystems, LLC reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to permit improvements in the per for mance, 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 in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, LLC assumes no re spon si bil i ty for its use; nor for any in fringe ment 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
Revision History
Revision Revision Date Description of Revision Rev. 4 December 20, 2012 Add information on CTAP, Automotive variant