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SG1731/SG2731/SG3731
DC MOTOR PULSE WIDTH MODULATOR
DESCRIPTION
The SG1731 is a pulse width modulator circuit designed specifically for DC motor control. It provides a bi-directional pulse train output in response to the magnitude and polarity of an analog error signal input. The device is useful as the control element in motor-driven servo systems for precision positioning and speed control, as well as in audio modulators and amplifiers using carrier frequencies to 350 KHz. The circuit contains a triangle waveform oscillator, a wideband operational amplifier for error voltage generation, a summing/scaling network for level-shifting the triangle waveform, externally programmable PWM comparators and dual 100mA, 22V totem pole drivers with commutation diodes for full bridge output. A SHUTDOWN terminal forces the drivers into a floating high-impedance state when driven LOW. Supply voltage to the control circuitry and to the output drivers may be from either dual positive and negative supplies, or single-ended.
FEATURES
* * * * * * * 3.5V to 15V control supply 2.5V to 22V driver supply Dual 100mA source/sink output drivers 5KHz to 350KHz oscillator range High slew rate error amplifier Adjustable deadband operation Digital SHUTDOWN input
HIGH RELIABILITY FEATURES - SG1731
Available to MIL-STD-883 LMI level "S" processing available
BLOCK DIAGRAM
4/90 Rev 1.3 9/99
Copyright 1999
1
11861
Western
LINFINITY
Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
Microelectronics
Inc.
SG1731/SG2731/SG3731
ABSOLUTE MAXIMUM RATINGS (Note1)
Supply Voltage (VS) ........................................................ 18V Analog Inputs ....................................................................... VS Digital Inputs (SHUTDOWN) .................... -VS-0.3V to -VS+18V Output Driver Supply Voltage (VO) ................................. 25V Source/Sink Output Current (continuous) .................... 200mA Source/Sink Output Current (peak, 500ns) .................. 400mA
Note 1. Values beyond which damage may occur.
Output Driver Diode Current (continuous) .................... 200mA Output Driver Diode Current (peak, 500ns) .................. 400mA Operating Junction Temperature Hermetic (J - Package) ............................................... 150C Plastic (N - Package) .................................................. 150C Storage Temperature Range ............................ -65C to 150C Lead Temperature (Soldering, 10 Seconds) .................. 300C
THERMAL DATA
J Package: Thermal Resistance-Junction Thermal Resistance-Junction N Package: Thermal Resistance-Junction Thermal Resistance-Junction to Case, JC .............. 30C/W to Ambient, JA .......... 80C/W to Case, JC .............. 40C/W to Ambient, JA ......... 65C/W
Note A. Junction Temperature Calculation: TJ = TA + (PD x JA). Note B. The above numbers for JC are maximums for the limiting thermal resistance of the package in a standard mounting configuration. The JA numbers are meant to be guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow.
RECOMMENDED OPERATING CONDITIONS (Note 2)
Supply Voltage Range (VS) ............................... 3.5V to 15V Error Amp Common-Mode Range ............... -VS + 3V to VS - 3V Output Driver Supply Voltage Range .................. 2.5V to 22V Source/Sink Output Current (continuous) .................... 100mA Source/Sink Output Current (peak, 500ns) .................. 200mA Output Driver Diode Current (continuous) .................... 100mA Output Driver Diode Current (peak, 500ns) .................. 200mA Oscillator Frequency Range ........................... 10Hz to 350KHz Oscillator Voltage (Peak-to-Peak) ............................. 1V to 10V Oscillator Timing Capacitor (CT) ....................... 200pF to 2.5F Operating Ambient Temperature Range SG1731 ........................................................ -55C to 125C SG2731 ........................................................... -25C to 85C SG3731 .............................................................. 0C to 70C
Note 2. Range over which the device is functional and parameter limits are guaranteed.
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specfiications apply over the operating ambient temperatures for SG1731 with -55C TA 125C, SG2731 with -25C TA 85C, SG3731 with 0C TA 70C, VS = 15V, and VO = 22V. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)
Parameter Oscillator Section CT Charging Current 2V Input Bias Current Initial Oscillator Frequency Temperature Stability (Note 3) Error Amplifier Section (Note 5) Input Offset Voltage Input Bias Current Input Offset Current Open Loop Voltage Gain Output Voltage Swing Common-Mode Rejection Ratio Slew Rate (Notes 3 and 4) Unity Gain Bandwidth (Notes 3 and 4) PWM Comparators Input Bias Current
Test Conditions TA = 25C TA = TMIN to TMAX VCM = 5V CT = 1000pF, 2V = 5V,TA = 25C CT = 1000pF, 2V = 5V
SG1731/2731/3731 Units Min. Typ. Max. 450 400 22.5 500 550 600 -20 27.5 10 10 3 600 A A A KHz % mV A nA dB V dB V/s MHz A
25.0
RL = 2K RL = 2K TA = 25C TA = 25C VT = 3V
70 10 70 5 0.7
10 1 6
4/90 Rev 1.3 9/99
Copyright 1999
2
11861
Western
LINFINITY
Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
Microelectronics
Inc.
SG1731/SG2731/SG3731
ELECTRICAL CHARACTERISTICS
Parameter SHUTDOWN Section Logic Threshold SHUTDOWN HIGH Current SHUTDOWN LOW Current Output Drivers (Each Output) HIGH Output Voltage LOW Output Voltage Driver Risetime Driver Falltime Total Supply Current VS Supply Current VO Supply Current
(continued)
Test Conditions -VS = -3.5V to -15V VSHUTDOWN = -VS+2.4V VSHUTDOWN = -VS ISOURCE = 20mA ISOURCE = 100mA ISINK = 20mA ISINK = 100mA CL = 1000pF CL = 1000pF VSHUTDOWN = -VS + 0.8V VSHUTDOWN = -VS + 0.8V
Note 5. VCM = 12V.
SG1731/2731/3731 Units Min. Typ. Max. VS+0.8 VS+2.0 400 -1.0 V A mA V V V V ns ns mA mA
19.2 19.0 -19.2 -19.0 300 300 14 6
Note 3. These parameters, although guaranteed, are not tested in production. Note 4. Unity Gain Inverting 10K Feedback Resistance.
APPLICATION INFORMATION
SUPPLY VOLTAGE The SG1731 requires a supply voltage for the control circuitry (VS) and for the power output drivers (VO). Each supply may be either balanced positive and negative with respect to ground, or singleended. The only restrictions are: 1. The voltage between +VS and -VS must be at least 7.0V; but no more than 44V. 2. The voltage between +VO and -VO must be at least 5.0V; but no more than 44V. 3. +VO must be at least 5V more positive than -VS. This eliminates the combination of a single-ended positive control supply with a single-ended negative driver supply. SUBSTRATE CONNECTION The substrate connection (Pin 10) must always be connected to either -VS or -VO, whichever is more negative. The substrate must also be well bypassed to ground with a high quality capacitor. OSCILLATOR The triangle oscillator consists of two voltage comparators, a set/ reset flip-flop, a bi-directional 500A current source, and an external timing capacitor CT. A positive reference voltage (2V+) applied to Pin 2 determines the positive peak value of the triangle, and a negative reference voltage (2V-) at Pin 7 sets the negative peak value of the triangle waveform. Since the value of the internal current source is fixed at a nominal 500A, the oscillator period is a function of the selected peakto-peak voltage excursion and the value of CT. The theoretical expression for the oscillator period is: (Eq.1) 5 x 10-4 where CT is the timing capacitor in Farads and dV is VOSC in Volts peak-to-peak.
4/90 Rev 1.3 9/99
Copyright 1999 FIGURE 1 - SG1731 OSCILLATOR PERIOD VS. VOSC AND CT
As a design aid, the solutions to Equation 1 over the recommended range of TOSC and VOSC are given in graphic form in Figure 1. The lower limit on TOSC is 1.85s, corresponding to a maximum frequency of 350 KHz. The maximum value of VOSC, (2V+) - (2V-), is 10V peak-to-peak for linear waveforms.
ERROR AMPLIFIER The error amplifier of the SG1731 is a conventional internallycompensated operational amplifier with low output impedance. All of the usual feedback and frequency compensation techniques may be use to control the closed-loop gain characteristics. The control supply voltage VS will determine the input common mode range and output voltage swing; both will extend to within 3V of the VS supply. PULSE WIDTH MODULATION Pulse width modulation occurs by comparing the triangle waveform to a fixed upper (+VT) and lower (-VT) threshold voltage. A crossing above the upper threshold causes Output A to switch to the HIGH state, and a crossing below
TOSC =
2CT dV
3
11861
Western
LINFINITY
Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
Microelectronics
Inc.
SG1731/SG2731/SG3731
APPLICATION INFORMATION
(continued)
the lower threshold causes Output B to switch to the HIGH state. If VS is less than 8V then VT can be obtained with resistors from VS. If VS is greater than 8V use zeners. Threshold crossings are generated by shifting the triangle waveform up and down with the error voltage (Pin 5). A positive error voltage will result in a pulse width modulated output at Driver A (Pin 13). Similarly, a negative error voltage produces a pulse train at Driver B (Pin 12). Figure 2 illustrates this process for the case where V+ is greater than VT. It is important to note that the triangle shifting circuit also attenuates the waveform seen at CT by a factor of 2. This results in a waveform at the PWM comparators with a positive peak of V+ and a negative peak of V-, and must be taken into account when selecting the values for +VT and -VT.
FIGURE 2 - PULSE WIDTH MODULATION WITH NO DEADBAND
APPLICATION CIRCUITS
FIGURE 3
FIGURE 4
In this simple battery-powered position servo, the control supply and driver supply are both single-ended positive with respect to ground.
A high torque position servo is obtained by buffering the output drivers to obtain higher output current.
4/90 Rev 1.3 9/99
Copyright 1999
4
11861
Western
LINFINITY
Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
Microelectronics
Inc.
SG1731/SG2731/SG3731
APPLICATION CIRCUITS
FIGURE 5
FIGURE 6
Bi-directional speed control results when the feedback voltage transducer is a tachometer.
The two-quadrant transfer function of the SG1731 is ideal for pulse width modulated audio power amplifiers.
(See Note Below)
CONNECTION DIAGRAMS & ORDERING INFORMATION
Package
16-PIN CERAMIC DIP J - PACKAGE
Part No. SG1731J/883B SG1731J SG2731J SG3731J SG2731N SG3731N
Ambient Temperature Range -55C to 125C -55C to 125C -25C to 85C 0C to 65C -25C to 85C 0C to 65C
Connection Diagram
+VT 2V+ N. I. INPUT INV. INPUT ERROR CT 2V-VT
1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9
16-PIN PLASTIC DIP N - PACKAGE
+VS SHUTDOWN +VO OUTPUT A OUTPUT B -VO SUBSTRATE -VS
Note 1. All packages are viewed from the top. Note 2. Contact factory for flatpack and leadless chip carrier availability. 4/90 Rev 1.3 9/99
Copyright 1999 11861 Western
LINFINITY
5
Avenue Garden Grove, CA 92841 (714) 898-8121 FAX: (714) 893-2570
Microelectronics
Inc.

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