LINEAR Upgrade Your Microcontroller ADC to True 12-Bit Performance Design Note DN463

Upgrade Your Microcontroller ADC to True 12-Bit Performance Design Note DN463 by Guy Hoover Introduction These ADCs are available in tiny 6-lead and 8-lead TSOT-

Many 8-bit and 16-bit microcontrollers feature 10-bit 23 packages. The 8-lead devices have adjustable VREF internal ADCs. A few include 12-bit ADCs, but these often and OVDD pins. The adjustable VREF pin allows the input have poor or nonexistent AC specifi cations, and certainly span to be reduced to 1.4V. This, combined with the high lack the performance to meet the needs of an increasing ADC input impedance, can eliminate the need for gain or number of applications. The LTC®2366 and its slower buffer stages in many applications. The OVDD pin, which speed versions offer a high performance alternative, as controls the digital output level, can be adjusted from 1V shown in the AC specifi cations in Table 1. Compare these to 3.6V, simplifying communication with different logic guaranteed specifi cations with the ADC built into your families. For applications that do not require an adjustable current microcontroller. reference or adjustable output levels, the 6-lead device with VREF = OVDD = VDD should suffi ce.

This family’s DC specifi cations are equally impressive. INL

FO IE FO

and DNL are guaranteed to be less than ±1LSB. Operating The SPI interface requires only three wires to communicate from a single 2.5V, 3V or 3.3V supply, the current draw with the microcontroller, keeping the overall solution size on these parts is a maximum of 4m A during a conver- small in low power, high speed applications.

sion. This can be reduced to less than 1μA by placing L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

the part into SLEEP mode during periods of inactivity, which greatly reduces the average supply current at lower sample rates.

3.3V 8192 Pt FFT

f S = 2.84MHz –20 VIN = –1d B AT 20k Hz C5 C4 SNR = 72.1d B

R1 0.1μF 10μF –40 THD = –70.1d B 1k R2

1k VDD VREF OVDD

AGND AGND –60

LT6202 AIN LTC2366 SCK

AGND 499Ω

24.9Ω SDO –100

1μF dn463 F01 –120

AGND AV=–4 2.0k

AGND AGND

Figure 1. Single Supply AC-Coupled Amplifi er Level Shifts Input for

FREQUENCY (MHz)

Maximum Dynamic Range dn463 F02

Figure 2. FFT Shows Low Noise and Distortion of Figure 1 Circuit