Path: EDN Asia >> Design Centre >> IC/Board/Systems Design >> Power precision SAR ADC with ultra-low power switcher
IC/Board/Systems Design Share print

Power precision SAR ADC with ultra-low power switcher

12 Apr 2016  | Alan Walsh

Share this page with your friends

This level of ripple showing up in the ADC output is extremely low for a 16 bit converter, 5 uV pk-pk corresponds to 0.07 lsb at 16 bits. Ripple at this level is buried in the ADC noise floor and requires a large amount of averaging to uncover it and will not be seen in many applications. This output ripple corresponds to a PSRR of


This measurement is similar to what is shown in figure 1 for the AD7980 PSRR of ~77 dB at 4.5kHz.


Figure 3: AD7980 and ADP5300 application circuit.


Figure 4: ADP5300 hysteretic switching ripple (AC coupled) when supplying the AD7980 and ripple tone in ADC FFT output at 1 MSPS throughput.


If the ADC throughput is reduced to 10 kSPS then the current consumption of the ADC scales linearly down to 15 uA (factor of ~100) and correspondingly the switching frequency ripple of the ADP5300 scales to 46.5Hz (factor of ~100) with an amplitude of 55 mV pk-pk (figure 5). The ripple shows up in the ADC FFT output at 46Hz again with an amplitude of -120 dB (5 uV pk-pk) because the PSRR is similar at this frequency. There is evidence of a second harmonic at 93Hz that is -125 dB down.


Figure 5: ADP5300 hysteretic switching ripple (AC coupled) when supplying the AD7980 and ripple tone in ADC FFT output at 10 KSPS throughput.


ADP5300 vs. LDO
Figure 6 shows how the efficiency of the ADP5300 stacks up versus that of an LDO across ADC throughput rate when regulating a 2.5V output from a 5V rail. As you would expect the switcher is far more efficient at delivering power than the LDO, 90% vs 50% (for a 5V input) at 1 MSPS and holds up much better at lower ADC throughputs/lower current consumption, staying above 80% until 5 KSPS.

At an ADC throughput of 1 MSPS using an LDO the current consumed from a 5V rail is 1.5 mA or 7.5 mW. Using the ADP5300 the current consumed from a 5V rail is 828 uA or 4.1 mW. This is a 3.4 mW or 45% reduction in the power drawn by the ADC power supply.


Figure 6: Efficiency vs ADC throughput for ADP5300 and LDO.


 First Page Previous Page 1 • 2 • 3 Next Page Last Page


Want to more of this to be delivered to you for FREE?

Subscribe to EDN Asia alerts and receive the latest design ideas and product news in your inbox.

Got to make sure you're not a robot. Please enter the code displayed on the right.

Time to activate your subscription - it's easy!

We have sent an activate request to your registerd e-email. Simply click on the link to activate your subscription.

We're doing this to protect your privacy and ensure you successfully receive your e-mail alerts.


Add New Comment
Visitor (To avoid code verification, simply login or register with us. It is fast and free!)
*Verify code:
Tech Impact

Regional Roundup
Control this smart glass with the blink of an eye
K-Glass 2 detects users' eye movements to point the cursor to recognise computer icons or objects in the Internet, and uses winks for commands. The researchers call this interface the "i-Mouse."

GlobalFoundries extends grants to Singapore students
ARM, Tencent Games team up to improve mobile gaming


News | Products | Design Features | Regional Roundup | Tech Impact