plest software interface requires only three 8-bit transfers

to perform a conversion (one 8-bit transfer to configure

the ADC, and two more 8-bit transfers to clock out the

10-bit conversion result). See Figure 19 for MAX1248/

MAX1249 QSPI connections.

Simple Software Interface

Make sure the CPU’s serial interface runs in master

mode so the CPU generates the serial clock. Choose a

clock frequency from 100kHz to 2MHz.

1) Set up the control byte for external clock mode and

call it TB1. TB1 should be of the format: 1XXXXX11

binary, where the Xs denote the particular channel

and conversion mode selected.

2) Use a general-purpose I/O line on the CPU to pull

CS low.

3) Transmit TB1 and, simultaneously, receive a byte

and call it RB1. Ignore RB1.

4) Transmit a byte of all zeros ($00 hex) and, simulta-

neously, receive byte RB2.

5) Transmit a byte of all zeros ($00 hex) and, simulta-

neously, receive byte RB3.

6) Pull CS high.

Figure 5 shows the timing for this sequence. Bytes RB2

and RB3 contain the result of the conversion padded

with one leading zero, two sub-bits, and three trailing

zeros. The total conversion time is a function of the

serial-clock frequency and the amount of idle time

between 8-bit transfers. To avoid excessive T/H droop,

make sure the total conversion time does not exceed

120µs.

Digital Output

In unipolar input mode, the output is straight binary

(Figure 16). For bipolar inputs, the output is two’s com-

plement (Figure 17). Data is clocked out at the falling

edge of SCLK in MSB-first format.

Clock Modes

The MAX1248/MAX1249 may use either an external

serial clock or the internal clock to perform the succes-

sive-approximation conversion. In both clock modes,

the external clock shifts data in and out of the

MAX1248/MAX1249. The T/H acquires the input signal

as the last three bits of the control byte are clocked into

DIN. Bits PD1 and PD0 of the control byte program the

clock mode. Figures 6–9 show the timing characteristics

common to both modes.

External Clock

In external clock mode, the external clock not only shifts

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

version steps. SSTRB pulses high for one clock period

after the last bit of the control byte. Successive-approxi-

mation bit decisions are made and appear at DOUT on

each of the next 10 SCLK falling edges (Figure 5).

SSTRB and DOUT go into a high-impedance state when

+2.7V to +5.25V, Low-Power, 4-Channel,

Serial 10-Bit ADCs in QSOP-16

10

______________________________________________________________________________________

SEL2

SEL1

SEL0

CH0

CH1

CH2

CH3

COM

0

0

1

+

–

1

0

1

+

–

0

1

0

+

–

1

1

0

+

–

Table 2. Channel Selection in Single-Ended Mode (SGL/

D

DIIF

F = 1)

SEL2

SEL1

SEL0

CH0

CH1

CH2

CH3

0

0

1

+

–

0

1

0

+

–

1

0

1

–

+

1

1

0

–

+

Table 3. Channel Selection in Differential Mode (SGL/

D

DIIF

F = 0)