UC1625 UC2625 UC3625 Brushless DC Motor Controller FEATURES DESCRIPTION * Drives Power MOSFETs or Power Darlingtons Directly * 50V Open Collector High--Side Drivers * Latched Soft Start * High--speed Current--Sense Amplifier with Ideal Diode The UC1625 and UC3625 motor controller ICs integrate most of the functions required for high-performance brushless DC motor control into one package. When coupled with external power MOSFETs or Darlingtons, these ICs perform fixed-frequency PWM motor control in either voltage or current mode while implementing closed loop speed control and braking with smart noise rejection, safe direction reversal, and cross-conduction protection. * Pulse--by--Pulse and Average Current Sensing * Although specified for operation from power supplies between 10V and 18V, the UC1625 can control higher voltage power devices Over--Voltage and Under--Voltage Protection with external level-shifting components. The UC1625 contains fast, high-current push-pull drivers for low-side power devices and 50V Direction Latch for Safe Direction Reversal open-collector outputs for high-side power devices or level shifting circuitry. Tachometer * Trimmed Reference Sources 30mA * * * The UC1625 is characterized for operation over the military temperature range of -55C to +125C, while the UC2625 is Programmable Cross--Conduction Protection characterized from -40C to +105C and the UC3625 is characterized from 0C to 70C. (NOTE: ESD Protection to 2kV) BLOCK DIAGRAM 11/97 UDG-92029-1 UC1625 UC2625 UC3625 ABSOLUTE MAXIMUM RATINGS VCC Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +20V Pwr VCC Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . +20V PWM In . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to 6V E/A IN(+), E/A IN(-) . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to 12V ISENSE1, ISENSE2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . -1.3 to 6V OV-Coast, Dir, Speed-In, SSTART, Quad Sel . . . . . . -0.3 to 8V H1, H2, H3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to 12V PU Output Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to 50V PU Output Current . . . . . . . . . . . . . . . . . . +200 mA continuous PD Output Current . . . . . . . . . . . . . . . . . . 200 mA continuous E/A Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 mA I SENSE Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . -10 mA Tach Out Output Current . . . . . . . . . . . . . . . . . . . . . . . . 10 mA VREF Output Current . . . . . . . . . . . . . . . . . . -50 mA continuous Operating Temperature Range UC1625. . . . . . -55C to 125C Operating Temperature Range UC2625. . . . . . -40C to 105C Operating Temperature Range UC3625. . . . . . . . . 0C to 70C Note 1: Currents are positive into and negative out of the specified terminal. Note 2: Consult Unitrode Integrated Circuits databook for information regarding thermal specifications and limitations of packages. CONNECTION DIAGRAM DIL-28 (TOP VIEW) J or N PACKAGE Note 3: This pinout applies to the SOIC (DW), PLCC (Q), and LCC (L) packages (ie. pin 22 has the same function on all packages.) ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for: TA = 25C; Pwr VCC = VCC = 12V; ROSC = 20k to VREF; COSC = 2nF; RTACH = 33k; CTACH = 10nF; and all outputs unloaded. TA = TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 14.5 30.0 mA Overall Supply current Over Operating Range VCC Turn-On Threshold Over Operating Range 8.65 8.95 9.45 V VCC Turn-Off Threshold Over Operating Range 7.75 8.05 8.55 V Over Operating Range Overvoltage/Coast OV-Coast Inhibit Threshold 1.65 1.75 1.85 V OV-Coast Restart Threshold 1.55 1.65 1.75 V OV-Coast Hysteresis 0.05 0.10 0.15 V OV-Coast Input Current -10 -1 0 A 0.8 1.0 1.2 V Logic Inputs H1, H2, H3 Low Threshold Over Operating Range H1, H2, H3 High Threshold Over Operating Range H1, H2, H3 Input Current Over Operating Range, to 0V Quad Sel, Dir Thresholds Over Operating Range 1.6 1.9 2.0 V -400 -250 -120 A 0.8 1.4 2.0 V Quad Sel Hysteresis 70 mV Dir Hysteresis 0.6 V Quad Sel Input Current -30 50 150 A Dir Input Current -30 -1 30 A -5.0 -0.1 5.0 A 0 3 PWM Amp/Comparator E/A In(+), E/A In(-) Input Current To 2.5V PWM In Input Current To 2.5V Error Amp Input Offset 0V < VCOMMON-MODE < 3V Error Amp Voltage Gain -10 70 E/A Out Range 30 A 10 mV 90 0.25 dB 3.50 V SSTART Pull-up Current To 0V -16 -10 -5 A SSTART Discharge Current To 2.5V 0.1 0.4 3.0 mA 2 UC1625 UC2625 UC3625 ELECTRICAL CHARACTERISTICS (cont): Unless otherwise stated, these specifications apply for: TA = 25C; Pwr VCC = VCC = 12V; ROSC = 20k to VREF; COSC = 2nF; RTACH = 33k; CTACH = 10nF; and all outputs unloaded. TA = TJ. PARAMETER TEST CONDITIONS MIN TYP 0.1 0.2 0.3 V ISENSE1 = .3V, ISENSE2 = .5V to .7V 1.75 1.95 2.15 V/V ISENSE1 = .3V, ISENSE2 = .3V 2.4 2.5 2.65 V SSTART Restart Threshold MAX UNITS Current Amp Gain Current Amp (cont.) Level Shift Peak Current Threshold ISENSE1 = 0V, Force ISENSE2 0.14 0.20 0.26 V Over Current Threshold ISENSE1 = 0V, Force ISENSE2 0.26 0.30 0.36 V ISENSE1, ISENSE2 Input Current To 0V -850 ISENSE1, ISENSE2 Offset Current To 0V -320 2 0 12 A 2 V V Range ISENSE1, ISENSE2 -1 A Tachometer/Brake Tach-Out High Level Over Operating Range, 10k to 2.5V Tach-Out Low Level Over Operating Range, 10k to 2.5V On Time 4.7 5 5.3 0.2 V 170 220 280 s 0.1 % -1.9 mA On Time Change With Temp Over Operating Range RC-Brake Input Current To 0V -4.0 Threshold to Brake, RC-Brake Over Operating Range 0.8 Brake Hysteresis, RC-Brake Speed-In Threshold 1.0 1.2 0.09 Over Operating Range Speed-In Input Current V V 220 257 290 mV -30 -5 30 A Low-Side Drivers Voh, -1mA, Down From VCC Over Operating Range 1.60 2.1 V Voh, -50mA, Down From VCC Over Operating Range 1.75 2.2 V Vol, 1mA Over Operating Range 0.05 0.4 V Vol, 50mA Over Operating Range 0.36 0.8 Rise/Fall Time 10% to 90% Slew Time, into 1nF 50 Vol, 1mA Over Operating Range 0.1 0.4 Vol, 50mA Over Operating Range 1.0 1.8 V Leakage Current Output Voltage = 50V 25 A Fall Time 10% to 90% Slew Time, 50mA Load V ns High-Side Drivers 50 V ns Oscillator Frequency Frequency 40 Over Operating Range 50 35 60 kHz 65 kHz Reference Output Voltage 4.9 5.0 5.1 V Output Voltage Over Operating Range 4.7 5.0 5.3 V Load Regulation 0mA to -20mA Load -40 -5 Line Regulation 10V to 18V VCC -10 -1 10 mV Short Circuit Current Over Operating Range 50 100 150 mA mV Miscellaneous Output Turn-On Delay 1 s Output Turn-Off Delay 1 s 3 UC1625 UC2625 UC3625 PIN DESCRIPTIONS Connect these inputs to motor shaft position sensors that are positioned 120 electrical degrees apart. If noisy signals are expected, zener clamp and filter these inputs with 6V zeners and an RC filter. Suggested filtering components are 1k and 2nF. Edge skew in the filter is not a problem, because sensors normally generate modified Gray code with only one output changing at a time, but rise and fall times must be shorter than 20s for correct tachometer operation. Dir, Speed-In: The position decoder logic translates the Hall signals and the Dir signal to the correct driver signals (PUs and PDs). To prevent output stage damage, the signal on Dir is first loaded into a direction latch, then shifted through a two-bit register. As long as Speed-In is less than 250mV, the direction latch is transparent. When Speed-In is higher than 250mV, the direction latch inhibits all changes in direction. Speed-In can be connected to Tach-Out through a filter, so that the direction latch is only transparent when the motor is spinning slowly, and has too little stored energy to damage power devices. Motors with 60 electrical degree position sensor coding can be used if one or two of the position sensor signals is inverted. Additional circuitry detects when the input and output of the direction latch are different, or when the input and output of the shift register are different, and inhibits all output drives during that time. This can be used to allow the motor to coast to a safe speed before reversing. ISENSE1, ISENSE2, ISENSE: The current sense amplifier has a fixed gain of approximately two. It also has a builtin level shift of approximately 2.5 volts. The signal appearing on ISENSE is: ISENSE = 2.5V + ( 2 * ABS ( ISENSE1 - ISENSE2 ) ) The shift register guarantees that direction can't be changed instantaneously. The register is clocked by the PWM oscillator, so the delay between direction changes is always going to be between one and two oscillator periods. At 40kHz, this corresponds to a delay of between 25s and 50s. Regardless of output stage, 25s dead time should be adequate to guarantee no overlap crossconduction. Toggling DIR will cause an output pulse on Tach-Out regardless of motor speed. ISENSE1 and ISENSE2 are interchangeable and can be used as differential inputs. The differential signal applied can be as high as 0.5V before saturation. If spikes are expected on ISENSE1 or ISENSE2, they are best filtered by a capacitor from ISENSE to ground. Filtering this way allows fast signal inversions to be correctly processed by the absolute value circuit. The peakcurrent comparator allows the PWM to enter a currentlimit mode with current in the windings never exceeding approximately 0.2V/RSENSE. The over current comparator provides a fail-safe shutdown in the unlikely case of current exceeding 0.3V/RSENSE. Then, soft start is commanded, and all outputs are turned off until the high current condition is removed. It is often essential to use some filter driving ISENSE1 and ISENSE2 to reject extreme spikes and to control slew rate. Reasonable starting values for filter components might be 250 series resistors and a 5nF capacitor between ISENSE1 and ISENSE2. Input resistors should be kept small and matched to maintain gain accuracy. E/A In(+), E/A In(-), E/A Out, PWM In: E/A In(+) and E/A In(-) are not internally committed to allow for a wide variety of uses. They can be connected to the ISENSE, to Tach-Out through a filter, to an external command voltage, to a D/A converter for computer control, or to another op amp for more elegant feedback loops. The error amplifier is compensated for unity gain stability, so E/A Out can be tied to E/A In(-) for feedback and major loop compensation. E/A Out and PWM In drive the PWM comparator. For voltage-mode PWM systems, PWM In can be connected to RC-Osc. The PWM comparator clears the PWM latch, commanding the outputs to chop. OV-Coast: This input can be used as an over-voltage shutdown in put, as a coast input, or both. This input can be driven by TTL, 5V CMOS, or 12V CMOS. The error amplifier can be biased off by connecting E/A In(-) to a higher voltage than E/A In(+). When biased off, E/A Out will appear to the application as a resistor to ground. E/A Out can then be driven by an external amplifier. PDA, PDB, PDC: These outputs can drive the gates of N-Channel power MOSFETs directly or they can drive the bases of power Darlingtons if some form of current limiting is used. They are meant to drive low-side power devices in high-current output stages. Current available from these pins can peak as high as 0.5A. These outputs feature a true totem-pole output stage. Beware of exceeding IC power dissipation limits when using these outputs for high continuous currents. These outputs pull high to turn a "low-side" device on (active high). GND: All thresholds and outputs are referred to the GND pin except for the PD and PU outputs. H1, H2, H3: The three shaft-position sensor inputs consist of hysteresis comparators with input pull-up resistors. Logic thresholds meet TTL specifications and can be driven by 5V CMOS, 12V CMOS, NMOS, or open-collectors. 4 UC1625 UC2625 UC3625 PIN DESCRIPTIONS (cont.): the low-side devices will brake the motor with current control. (See applications) Simpler current sense connections will result in uncontrolled braking and potential damage to the power devices. PUA, PUB, PUC: These outputs are open-collector, high-voltage drivers that are meant to drive high-side power devices in high-current output stages. These are active low outputs, meaning that these outputs pull low to command a high-side device on. These outputs can drive low-voltage PNP Darlingtons and P-channel MOSFETs directly, and can drive any high-voltage device using external charge-pump techniques, transformer signal coupling, cascode level-shift transistors, or optoisolated drive. (See applications). RC-Osc: The UC3625 can regulate motor current using fixed-frequency pulse width modulation (PWM). The RCOsc pin sets oscillator frequency by means of timing resistor ROSC from the RC-Osc pin to VREF and capacitor COSC from RC-Osc to Gnd. Resistors 10k to 100k and capacitors 1nF to 100nF will work best, but frequency should always be below 500kHz. Oscillator frequency is approximately: PWR VCC: This supply pin carries the current sourced by the PD outputs. When connecting PD outputs directly to the bases of power Darlingtons, the PWR VCC pin can be current limited with a resistor. Darlington outputs can also be "Baker Clamped" with diodes from collectors back to PWR VCC. (See Applications) F = 2 / ROSCCOSC Additional components can be added to this device to cause it to operate as a fixed off-time PWM rather than a fixed frequency PWM, using the RC-Osc pin to select the monostable time constant. Quad Sel: The IC can chop power devices in either of two modes, referred to as "two-quadrant" (Quad Sel low) and "four-quadrant" (Quad Sel high). When two-quadrant chopping, the pull-down power devices are chopped by the output of the PWM latch while the pull-up drivers remain on. The load will chop into one commutation diode, and except for back-EMF, will exhibit slow discharge current and faster charge current. Two-quadrant chopping can be more efficient than four-quadrant. When four-quadrant chopping, all power drivers are chopped by the PWM latch, causing the load current to flow into two diodes during chopping. This mode exhibits better control of load current when current is low, and is preferred in servo systems for equal control over acceleration and deceleration. The Quad Sel input has no effect on operation during braking. The voltage on the RC-Osc pin is normally a ramp of about 1.2V peak-to-peak, centered at approximately 1.6V. This ramp can be used for voltage-mode PWM control, or can be used for slope compensation in current-mode control. SSTART: Any time that VCC drops below threshold or the sensed current exceeds the over-current threshold, the soft-start latch is set. When set, it turns on a transistor that pulls down on SSTART. Normally, a capacitor is connected to this pin, and the transistor will completely discharge the capacitor. A comparator senses when the NPN transistor has completely discharged the capacitor, and allows the soft-start latch to clear when the fault is removed. When the fault is removed, the soft-start capacitor will charge from the on-chip current source. RC-Brake: Each time the Tach-Out pulses, the capacitor tied to RC-Brake discharges from approximately 3.33V down to 1.67V through a resistor. The tachometer pulse width is approximately T = 0.67 RT CT, where RT and CT are a resistor and capacitor from RC-Brake to ground. Recommended values for RT are 10k to 500k, and recommended values for CT are 1nF to 100nF, allowing times between 5s and 10ms. Best accuracy and stability are achieved with values in the centers of those ranges. SSTART clamps the output of the error amplifier, not allowing the error amplifier output voltage to exceed SSTART regardless of input. The ramp on RC-Osc can be applied to PWM In and compared to E/A Out. With SSTART discharged below 0.2V and the ramp minimum being approximately 1.0V, the PWM comparator will keep the PWM latch cleared and the outputs off. As SSTART rises, the PWM comparator will begin to dutycycle modulate the PWM latch until the error amplifier inputs overcome the clamp. This provides for a safe and orderly motor start-up from an off or fault condition. RC-Brake also has another function. If RC-Brake pin is pulled below the brake threshold, the IC will enter brake mode. This mode consists of turning off all three highside devices, enabling all three low-side devices, and disabling the tachometer. The only things that inhibit lowside device operation in braking are low-supply, exceeding peak current, OV-Coast command, and the PWM comparator signal. The last of these means that if current sense is implemented such that the signal in the current sense amplifier is proportional to braking current, Tach-Out: Any change in the H1, H2, or H3 inputs loads data from these inputs into the position sensor latches. At the same time data is loaded, a fixed-width 5V pulse is triggered on Tach-Out. The average value of the voltage on Tach-Out is directly proportional to speed, so this output can be used as a true tachometer for speed feedback with an external filter or averaging circuit. 5 UC1625 UC2625 UC3625 PIN DESCRIPTIONS (cont.): Whenever Tach-Out is high, the position latches are inhibited, such that during the noisiest part of the commutation cycle, additional commutations are not possible. Although this will effectively set a maximum rotational speed, the maximum speed can be set above the highest expected speed, preventing false commutation and chatter. ground with an 0.1F ceramic capacitor. Using a 10F electrolytic bypass capacitor as well can be beneficial in applications with high supply impedance. VREF: This pin provides regulated 5 volts for driving Halleffect devices and speed control circuitry. VREF will reach +5V before VCC enables, ensuring that Hall-effect devices powered from VREF will become active before the UC3625 drives any output. Although VREF is current limited, operation over 30mA is not advised. For proper performance VREF should be bypassed with at least a 0.1F capacitor to ground. VCC: This device operates with supplies between 10V and 18V. Under-voltage lockout keeps all outputs off below 7.5V, insuring that the output transistors never turn on until full drive capability is available. Bypass VCC to CROSS CONDUCTION PREVENTION The UC3625 inserts delays to prevent cross conduction due to overlapping drive signals. However, some thought must always be given to cross conduction in output stage design because no amount of dead time can prevent fast slewing signals from coupling drive to a power device through a parasitic capacitance. This prevents noise generated in the first 50s of a transition from propagating to the output transistors and causing cross-conduction or chatter. The UC3625 also contains six flip flops corresponding to the six output drive signals. One of these flip flops is set every time that an output drive signal is turned on, and cleared two PWM oscillator cycles after that drive signal is turned off. The output of each flip flop is used to inhibit drive to the opposing output. (see below) In this way, it is impossible to turn on driver PUA and PDA at the same time. It is also impossible for one of these drivers to turn on without the other driver having been off for at least two PWM oscillator clocks. The UC3625 contains input latches that serve as noise blanking filters. These latches remain transparent through any phase of a motor rotation and latch immediately after an input transition is detected. They remain latched for two cycles of the PWM oscillator. At a PWM oscillator speed of 20kHz, this corresponds to 50s to 100s of blank time which limits maximum rotational speed to 100kRPM for a motor with six transitions per rotation or 50kRPM for a motor with 12 transitions per rotation. 6 UC1625 UC2625 UC3625 TYPICAL CHARACTERISTICS: Oscillator Frequency vs COSC and ROSC Tachometer On Time vs RT and CT 100ms 1MHz 500 RT Ro sc On Time Oscillator Frequency 10ms 100kHz - 10 k 10kHz Ro sc - 30 k Ro sc - 10 RT - 1ms 100 RT 100s RT - k k 30k 10k 0k 1kHz 10s 1s 0.001 100Hz 0.001 0.01 0.1 0.01 CT (F) COSC (F) Supply Current vs Temperature Soft Start Pull-Up Current vs Temperature Soft Start Discharge Current vs Temperature 7 0.1 UC1625 UC2625 UC3625 POWER STAGE DESIGN: The UC3625 is useful in a wide variety of applications, including high-power in robotics and machinery. The power output stages used in such equipment can take a number of forms, according to the intended performance and purpose of the system. Below are four different power stages with the advantages and disadvantages of each shown. diodes go to ground and the current sense terminals of the UC3625 (ISENSE1 and ISENSE2) are connected to RT through an Rc filter. The input bias current of the current sense amplifier will cause a common mode offset voltage to appear at both inputs, so for best accuracy, keep the filter resistors below 2k and matched. The current that flows through RT is discontinuous because of chopping. It flows during the on time of the power stage and is zero during the off time. Consequently, the voltage across RT consists of a series of pulses, occurring at the PWM frequency, with a peak value indicative of the peak motor current. For high-frequency chopping, fast recovery circulating diodes are essential. Six are required to clamp the windings. These diodes should have a continuous current rating at least equal to the operating motor current, since diode conduction duty-cycle can be high. For lowvoltage systems, Schottky diodes are preferred. In higher voltage systems, diodes such as Microsemi UHVP high voltage platinum rectifiers are recommended. To sense average motor current instead of peak current, add another current sense resistor (RD in Figure D) to measure current in the low-side circulating diodes, and operate in four quadrant mode (pin 22 high). The negative voltage across RD is corrected by the absolute value current sense amplifier. Within the limitations imposed by Table 1, the circuit of Figure B can also sense average current. In a pulse-by-pulse current control arrangement, current sensing is done by resistor RT, through which the transistor's currents are passed (Figures A, B, and C). In these cases, RD is not needed. The low-side circulating 8 UC1625 UC2625 UC3625 POWER STAGE DESIGN (cont.): 2 QUADRANT 4 QUADRANT SAFE BRAKING POWER REVERSE FIGURE A YES NO NO FIGURE B YES YES NO FIGURE C YES YES YES FIGURE D YES YES YES NO jsa;hzh;ahfaxzh IN 4QUAD MODE ONLY IN 4QUAD MODE ONLY IN 4QUAD MODE ONLY Fast High-Side P-Channel Driver CURRENT SENSE PULSE BY AVERAGE PULSE YES NO YES YES YES NO YES YES Optocoupled N-Channel High-Side Driver 9 UC1625 UC2625 UC3625 For drives where speed is critical, P-Channel MOSFETs can be driven by emitter followers. Here, both the level shift NPN and the PNP must withstand high voltages. A zener diode is used to limit gate-source voltage on the MOSFET. A series gate resistor is not necessary, but always advisable to control overshoot and ringing. High-voltage optocouplers can quickly drive high-voltage MOSFETs if a boost supply of at least 10 volts greater than the motor supply is provided. To protect the MOSFET, the boost supply should not be higher than 18 volts above the motor supply. Power NPN High-Side Driver Power NPN Low-Side Driver For under 200V 2-quadrent applications, a power NPN driven by a small P-Channel MOSFET will perform well as a high-side driver. A high voltage small-signal NPN is used as a level shift and a high voltage low-current MOSFET provides drive. Although the NPN will not saturate if used within its limitations, the base-emitter resistor on the NPN is still the speed limiting component. This power NPN Darlington drive technique uses a clamp to prevent deep saturation. By limiting saturation of the power device, excessive base drive is minimized and turn-off time is kept fairly short. Lack of base series resistance also adds to the speed of this approach. 10 UC1625 UC2625 UC3625 Fast High-Side N-Channel Driver with Transformer Isolation A small pulse transformer can provide excellent isolation between the UC3625 and a high-voltage NChannel MOSFET while also coupling gate drive power. In this circuit, a UC3724 is used as a transformer driver/encoder that duty-cycle modulates the transformer with a 150kHz pulse train. The UC3725 rectifies this pulse train for gate drive power, demodulates the signal, and drives the gate with over 2 amp peak current. timing resistor of the UC3724 (1k minimum), lower the timing capacitor of the UC3724 (500pF minimum) or both. If there is significant capacitance between transformer primary and secondary, together with very high output slew rate, then it may be necessary to add clamp diodes from the transformer primary to +12V and ground. Signal diodes such as 1N4148 are normally adequate. The UC3725 also has provisions for MOSFET current limiting. Consult the UC3725 data sheet for more information on implementing this. Both the UC3724 and the UC3725 can operate up to 500kHz if the pulse transformer is selected appropriately. To raise the operating frequency, either lower the COMMUTATION TRUTH TABLE DIR 6 1 1 1 1 1 1 0 0 0 0 0 0 X X This table shows the outputs of the gate drive and open collector outputs for given hall input codes and direction signals. Numbers at the top of the columns are pin numbers. These ICs operate with position sensor encoding that has either one or two signals high at a time, never all low or all high. This coding is sometimes referred to as "120 Coding" because the coding is the same as coding with position sensors spaced 120 magnetic degrees about the rotor. In response to these position sense signals, only one low-side driver will turn on (go high) and one high-side driver will turn on (pull low) at any time. 11 INPUTS H1 H2 8 9 0 0 0 1 0 1 1 1 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 0 1 1 0 0 H3 10 1 1 0 0 0 1 1 0 0 0 1 1 1 0 OUTPUTS Low-Side High-Side 12 13 14 16 17 18 L H L L H H L L H L H H L L H H L H H L L H L H H L L H H L L H L H H L L L H H L H L L H L H H L H L L H H L H L H H L H L L H H L H L L H L H L L L H H H L L L H H H TYPICAL APPLICATION: A 45V/8A Brushless DC Motor Drive Circuit N-Channel power MOSFETs are used for low-side drivers, while P-Channel power MOSFETs are shown for high-side drivers. Resistors are used to level shift the UC3625 open-collector outputs, driving emitter followers into the MOSFET gate. A 12V zener clamp insures that the MOSFET gate-source voltage will never exceed 12V. Series 10 gate resistors tame gate reactance, preventing oscillations and minimizing ringing. UC1625 UC2625 UC3625 steady-state motor speed is closely related to applied voltage. Pin 20 (Tach-Out) is connected to pin 7 (SPEED IN) through an RC filter, preventing direction reversal while the motor is spinning quickly. In two-quadrant operation, this reversal can cause kinetic energy from the motor to be forced into the power MOSFETs. A diode in series with the low-side MOSFETs facilitates PWM current control during braking by insuring that braking current will not flow backwards through low-side MOSFETs. Dual current-sense resistors give continuous current sense, whether braking or running in four-quadrant operation, an unnecessary luxury for two-quadrant operation. The oscillator timing capacitor should be placed close to pins 15 and 25, to keep ground current out of the capacitor. Ground current in the timing capacitor causes oscillator distortion and slaving to the commutation signal. The potentiometer connected to pin 1 controls PWM duty cycle directly, implementing a crude form of speed control. This control is often referred to as "voltage mode" because the potentiometer position sets the average motor voltage. This controls speed because The 68k ohm and 3nF tachometer components set maximum commutation time at 140s. This permits smooth operation up to 35,000 RPM for four-pole motors, yet gives 140s of noise blanking after commutation. UNITRODE CORPORATION 7 CONTINENTAL BLVD. * MERRIMACK, NH 03054 TEL. (603) 424-2410 * FAX (603) 424-3460 12