Ultra-Low-Power, 22Msps, Dual 8-Bit ADC

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17

values originally held on C2a and C2b. These values

are then presented to the first stage quantizers and iso-

late the pipelines from the fast-changing inputs. The

wide input bandwidth T/H amplifiers allow the MAX1192

to track and sample/hold analog inputs of high frequen-

cies (>Nyquist). Both ADC inputs (INA+, INB+, INA-,

and INB-) can be driven either differentially or single

ended. Match the impedance of INA+ and INA-, as well

as INB+ and INB-, and set the common-mode voltage

Analog Inputs and Reference

Configurations

MAX1192 provides three modes of reference operation.

ation mode (Table 1).

to be 0.512V ±3%. COM, REFP, and REFN are low-

REFN, and COM each with a 0.33µF capacitor.

In buffered external reference mode, apply a 1.024V

±10% at REFIN. In this mode, COM, REFP, and REFN

Bypass REFP, REFN, and COM each with a 0.33µF

capacitor. Bypass REFIN to GND with a 0.1µF capacitor.

In unbuffered external reference mode, connect REFIN

to GND. This deactivates the on-chip reference buffers

for COM, REFP, and REFN. With their buffers shut

down, these nodes become high-impedance inputs

(Figure 4) and can be driven through separate, external

each with a 0.33µF capacitor.

For detailed circuit suggestions and how to drive this

dual ADC in buffered/unbuffered external reference

mode, see the Applications Information section.

Clock Input (CLK)

CLK accepts a CMOS-compatible signal level. Since

the interstage conversion of the device depends on the

repeatability of the rising and falling edges of the exter-

nal clock, use a clock with low jitter and fast rise and

fall times (<2ns). In particular, sampling occurs on the

rising edge of the clock signal, requiring this edge to

Figure 4. Unbuffered External Reference Mode Impedance

REFERENCE MODE

each with a 0.33µF capacitor.

1.024V ±10%

Buffered external reference mode. An external 1.024V ±10% reference voltage is applied to

0.33µF capacitor. Bypass REFIN to GND with a 0.1µF capacitor.

<0.3V

Unbuffered external reference mode. REFP, REFN, and COM are driven by external reference

REFN, and COM each with a 0.33µF capacitor.

Table 1. Reference Modes

MAX1192

1.5V

1.25V

1.75V

62.5

µA

0

µA

COM

REFN

REFP

4k

Ω

4k

Ω

62.5

µA