Datasheet LT1713, LT1714 (Analog Devices) - 16

LT1713/LT1714
U TYPICAL APPLICATIO
forte of this particular implementation is that it is rail-to- example, with their inherent lowpass characteristic. Care rail allowing a full-scale analog input. Once the triangle must be taken to avoid cross conduction in the output wave is achieved, the remainder of the pulse width modu- power transistors. lator is easy, and is constituted by doing a simple compari- The linearity of the pulse width modulated signal can easily son using the second half of the LT1714. The triangle wave be ascertained by putting a simple 2-pole RC filter at the and the relatively slow moving analog signal (the one to be output (as shown in Figure 9). This demodulates the signal modulated or to do the modulation, depending on how you which can then be viewed and compared with the original look at it) are fed into the inputs of comparator B, whose input signal on an oscilloscope. Using a spectrum analyzer output is then the PWM representation of the analog input and a 1kHz reference signal, this circuit’s distortion prod- voltage. The higher the analog input voltage, the wider the ucts were measured as better than – 50dBc (0.3%) to output pulse. The time averaged output level is thus about 3.5V proportional to the analog input voltage. This binary P-P, degrading to – 30dBc (3%) as the circuit clips at 5V output can then be fed into power transistors with direct P-P on a single 5V supply. control over motor or speaker winding current, for ANTIALIASING R1 1k FILTER ANALOG V+ 26.1Ω C1 INPUT 500pF C4 V+ R2 0.001µF 16kHz ANALOG FILTER 2k V+ FOR LINEARITY MEASUREMENT 2 + 4 14 7 5 A R4 V+ 1k 10k + R3 1 11 1/2 LT1714 13 499Ω 2 B 2k 1 – 1/2 LT1714 – 7 12 C5 C6 16 6 21Ω 8 0.01µF 0.001µF 15 LT1809 – 10 3 3 9 + C3 6 R5 4 100pF 171314 F09 1k V+ COMPLEMENTARY C2 R6 1MHz 1MHz PWM 0.01µF 1k TRIANGLE OUTPUTS V+ = 2.7V TO 7V WAVE
Figure 9. Rail-to-Rail 1MHz Pulse Width Modulator RELATED PARTS PART NUMBER DESCRIPTION COMMENTS
LT1016 UltraFast Precision Comparator Industry Standard 10ns Comparator LT1116 12ns Single Supply Ground Sensing Comparator Single Supply Version of the LT1016 LT1394 7ns, UltraFast Single Supply Comparator 6mA Single Supply Comparator LT1671 60ns, Low Power, Single Supply Comparator 450µA Single Supply Comparator LT1711/LT1712 Single/Dual, 4.5ns, 3V/5V/±5V Rail-to-Rail Comparators Faster Versions of LT1713/LT1714 LT1719 4.5ns, Single Supply 3V/5V Comparator 4mA Comparator with Rail-to-Rail Outputs LT1720/LT1721 Dual/Quad, 4.5ns, Single Supply Comparator Dual/Quad Version of the LT1719 171314f LT/TP 0501 4K • PRINTED IN USA 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 2000