SLAAE33 September   2021 DAC43204 , DAC43401 , DAC43701 , DAC43701-Q1 , DAC53204 , DAC53401 , DAC53701 , DAC53701-Q1 , LM555 , LMC555 , NA555 , NE555 , SA555 , SE555 , TLC555

 

  1.   Trademarks
  2. 1Introduction
  3. 2Functional Overview of 555 Timers vs. Smart DACs
  4. 3Pulse Generator with Variable Frequency and Variable Duty Cycle
  5. 4Analog Input to PWM Output
  6. 5General Purpose Input (GPI) to PWM Output
  7. 6Comparator with Hysteresis
  8. 7Trade-offs and Conclusions

7 Trade-offs and Conclusions

Using four common application circuits, it has been shown that smart DACs can provide superior performance when compared to 555 timers. There are still be use cases in which a 555 timer is the preferred device if the application calls for high voltage and/or high output current. TI has 555 timers with minimum supplies of 1.5 V (LMC555) or maximum supplies of 18 V (SE555) while smart DACs have a supply voltage range of 1.8 V to 5.5 V across the same temperature range. 555 timers can output as much as 200 mA of current, while smart DACs can output 10 mA.

For cost-effective solutions that do not require high accuracy, the 555 timer is still a useful building block, specifically if working with high voltage and or high output current applications. However, many modern use cases are for lower voltage supplies with lower output current requirements, and the smart DAC offers considerable benefits in these cases. Smart DACs can provide competitive pricing against 555 times, so for these applications contact factory for a quote.

Waveform creation with 555 timers relies on a collection of external components which — specifically in the case of external capacitors — can have wide tolerance variation. Smart DACs remove the need to rely on the variation of external capacitors for timing elements and can achieve much higher accuracy. Most errors can be calibrated out in production by reprogramming the device to achieve the desired output. In PWM applications, the DAC53701 smart DAC voltage to duty-cycle is a linear function with a less than 1% duty-cycle error while it is non-linear in the 555 timer with about a 5% duty-cycle error. The waveform timings are programmable in smart DACs using I2C or SPI and they can be recalled directly from EEPROM without a processor whereas 555 timers need a hardware update for every change.

For low voltage, low output current use cases, the combination of a smart DAC’s programmability, high accuracy with limited external components, and stored EEPROM configurations make it a superior choice to the 555 timer.

Table 7-1 Smart DAC vs. 555 Timer Comparison Table
Smart DAC (DAC53701)555 Timer (LMC555)555 Timer (SE555)
Accuracy<1% total unadjusted error (TUE) over temperature.17% initial device accuracy plus timing capacitor and resistor tolerance at room temperature.1.5% initial device accuracy plus timing capacitor and resistor tolerance at room temperature.
Solution size2.00mm × 2.00 mm package.

1.43mm × 1.41 mm package plus external timing capacitor and resistors.

4.90mm × 3.91 mm package plus external timing capacitor and resistors.

ConfigurabilityEEPROM to store timing settings. Reconfigurable using I2C or SPI communication.Timing settings defined by hardware. A hardware change is required to reconfigure the timing.Timing settings defined by hardware. A hardware change is required to reconfigure the timing.
Max Frequency (square wave mode)250kHz3MHz100kHz
Max Frequency (PWM mode)2.5kHz (1% to 99% duty cycle)16.7 kHz (12% to 98% duty cycle). Duty cycle range improves at lower frequencies.16.7 kHz (25% to 95% duty cycle). Duty cycle range improves at lower frequencies.
Voltageto duty cycle function typeLinearNon-linearNon-linear
Operating power supply1.8 V to 5.5 V1.5 V to 15 V4.5 V to 18 V
Operating temperature-40°Cto 125°C-40°Cto 125°C-40°Cto 125°C
Static Current (output high, no load)225µA100µA2mA
Current Output10mA source and sink50mA source, 10 mA sink200mA source and sink