Document
PRELIMINARY
ML4435 Sensorless BLDC Motor Controller
GENERAL DESCRIPTION
The ML4435 provides all the circuitry for sensorless speed control of 3 phase Brushless DC Motors. Controller functions include start-up circuitry, Back EMF commutation control, Pulse Width Modulation (PWM) speed control, pulse-by-pulse current limiting, motor coasting, and under-voltage protection. Motor starting is accomplished by commutating the motor at a low frequency to produce low speed motion. The low speed motion is used to generate a Back EMF signal. A back EMF sampling circuit locks on to the motors position and controls commutation timing by forming a phase locked loop (PLL). The commutation control circuitry also outputs a speed feedback signal used in the speed control loop. The speed control loop consists of an error amplifier and PWM comparator that produces a PWM duty cycle for speed regulation. Motor current is limited by a pulseby-pulse PWM shutdown comparator that is tripped by the voltage across an external current sense resistor. Commutation control, PWM speed control, and current limiting are combined to produce the output driver signals. Six output drivers are used to provide gating signals to an external 3 phase bridge power stage sized for the Brushless DC (BLDC) motor voltage and current requirements. Additional functions include a motor coast function and an under voltage lock out circuit to shut down the output drivers in the event of a low voltage condition on the VCC to the ML4435.
FEATURES
n Proprietary back-EMF sensing commutation technique for motor communication without hall effect sensors n PWM pulse-by-pulse current limiting to protect motor and FET drivers n Stand-alone operation; motor starts and stops with power applied to the IC* n Soft-start function limits start-up current n PWM speed control for efficiency and minimum FET sizing n Onboard under voltage lock out and power fail detect n Tach output senses commutation of the motor
* Some External Components Required.
PRELIMINARY DATASHEET
May, 2000
PRELIMINARY
ML4435
WARRANTY
Micro Linear makes no representations or warranties with respect to the accuracy, utility, or completeness of the contents of this publication and reserves the right to make changes to specifications and product descriptions at any time without notice. No license, express or implied, by estoppel or otherwise, to any patents or other intellectual property rights is granted by this document. The circuits contained in this document are offered as possible applications only. Particular uses or applications may invalidate some of the specifications and/or product descriptions contained herein. The customer is urged to perform its own engineering review before deciding on a particular application. Micro Linear assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale and/or use of Micro Linear products including liability or warranties relating to merchantability, fi tness for a particular purpose, or infringement of any intellectual property right. Micro Linear products are not designed for use in medical, life saving, or life sustaining applications.
© Micro Linear 2000. is a registered trademark of Micro Linear Corporation. All other trademarks are the property of their respective owners. Products described herein may be covered by one or more of the following U.S. patents: 4,897,611; 4,964,026; 5,027,116; 5,281,862; 5,283,483; 5,418,502; 5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376; 5,652,479; 5,661,427; 5,663,874; 5,672,959; 5,689,167; 5,714,897; 5,717,798; 5,742,151; 5,747,977; 5,754,012; 5,757,174; 5,767,653; 5,777,514; 5,793,168; 5,798,635; 5,804,950; 5,808,455; 5,811,999; 5,818,207; 5,818,669; 5,825,165; 5,825,223; 5,838,723; 5.844,378; 5,844,941. Japan: 2,598,946; 2,619,299; 2,704,176; 2,821,714. Other patents are pending.
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PRELIMINARY DATASHEET
May, 2000
PRELIMINARY
BLOCK DIAGRAM
ML4435
FB A 14 FB B 15 MUX 2.9kΩ FB C 16 COMMUTATION STATE MACHINE
R
NEUTRAL SIMULATOR 5.8kΩ
18 SPEED FB SIGN CHANGER
+ – + +
LEVEL SHIFT – 0.7V
COMP
0.97V
–
2 TACH
BACK EMF SAMPLER SPEED FB 6 VOLTAGE CONTROLLED OSCILLATOR
+
B
20 CVCO 4 RVCO
COMP
3µs POWER ON RESET PULSE
A F
1.5V SPEED ERROR AMP
+ – + –
–
COAST
0.9V
E D
C
SPEED SET 5 8.2 + 0.7V
7 HA GATING LOGIC AND OUTPUT DRIVERS 8 HB 9 HC 11 LA 12 LB 13 LC D Q PULSE-BY-PULSE CURRENT LIMIT R 8.7V
LEVEL SHIFT 0.7V
+ –
SPEED COMP 3 5V
PWM COMPARATOR
2.2 + 0.7V
TRIANGLE WAVE GENERATOR
ISENSE 1
+ –
1V 225kΩ
+ –
COMP
UVLO COMPARATOR
SOFT START 19 225kΩ
6V REFERENCE VREF + 0.7V
VREF
CURRENT LIMIT COMPARATOR
6 RT
10 VCC
17 GND
ML4435 Block Diagram
May, 2000
PRELIMINARY DATASHEET
3
PRELIMINARY
PIN CONFIGURATION
ML4435 20-P n PDIP P20 20-P n SOIC S20
ISENSE TACH SPEED COMP RVCO SPEED SET RT HA HB HC VCC 9 0 2 3 4 5 6 6 5 4 3 2 20 9 CVCO SOFT START SPEED FB ND FB C FB B FB A LC LB LA
ML4435
TOP VIEW
PIN DESCRIPTIONS
PIN N.