External Clock

In external clock mode, the external clock not only

shifts data in and out, it also drives the analog-to-digital

conversion steps. SSTRB pulses high for one clock

period after the last bit of the control byte.

Successive-approximation bit decisions are made and

appear at DOUT on each of the next 12 SCLK falling

edges (see Figure 6). The first 10 bits are the true data

bits, and the last two are sub-LSB bits.

SSTRB and DOUT go into a high-impedance state when

CS goes high; after the next CS falling edge, SSTRB will

output a logic low. Figure 8 shows the SSTRB timing in

external clock mode.

The conversion must complete in some minimum time, or

else droop on the sample-and-hold capacitors may

degrade conversion results. Use internal clock mode if the

clock period exceeds 10µs, or if serial-clock interruptions

could cause the conversion interval to exceed 120µs.

Internal Clock

In internal clock mode, the MAX192 generates its own

conversion clock internally. This frees the microproces-

sor from the burden of running the SAR conversion

clock, and allows the conversion results to be read

back at the processor’s convenience, at any clock rate

from zero to typically 10MHz. SSTRB goes low at the

start of the conversion and then goes high when the

conversion is complete. SSTRB will be low for a maxi-

mum of 10µs, during which time SCLK should remain

low for best noise performance. An internal register

stores data when the conversion is in progress. SCLK

clocks the data out at this register at any time after the

conversion is complete. After SSTRB goes high, the

next falling clock edge will produce the MSB of the

conversion at DOUT, followed by the remaining bits in

MSB-first format (Figure 9). CS does not need to be

held low once a conversion is started.

Low-Power, 8-Channel,

Serial 10-Bit ADC

______________________________________________________________________________________

11

0.1

µF

DGND

AGND

AGND

CS

SCLK

DIN

DOUT

SSTRB

SHDN

+5V

N.C.

0.01

µF

CH7

REFADJ

VREF

C2

0.01

µF

+2.5V

REFERENCE

C1

4.7

µF

0V TO

4.096V

ANALOG

INPUT

+2.5V

**

OSCILLOSCOPE

CH1

CH2

CH3

CH4

* FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FFF (HEX)

**OPTIONAL. A POTENTIOMETER MAY BE USED IN PLACE OF THE REFERENCE FOR TEST PURPOSES.

MAX192

+5V

2MHz

OSCILLATOR

SCLK

SSTRB

DOUT*

Figure 5. Quick-Look Circuit