Applications Information

Internal Reference

The MAX1077/MAX1079 have an on-chip voltage refer-

ence trimmed to 2.048V. The internal reference output

is connected to REF and also drives the internal capac-

itive DAC. The output can be used as a reference volt-

age source for other components and can source up to

2mA. Bypass REF with a 0.01µF capacitor and a 4.7µF

capacitor to RGND.

The internal reference is continuously powered up dur-

ing both normal and partial power-down modes. In full

power-down mode, the internal reference is disabled.

Be sure to allow at least 2ms recovery time after hard-

ware power-up or exiting full power-down mode for the

reference to reach its intended value.

How to Start a Conversion

An analog-to-digital conversion is initiated by CNVST

and clocked by SCLK, and the resulting data is clocked

out on DOUT by SCLK. With SCLK idling high or low, a

falling edge on CNVST begins a conversion. This causes

the analog input stage to transition from track to hold

mode and DOUT to transition from high impedance to

being actively driven low. A total of 16 SCLK cycles are

required to complete a normal conversion. If CNVST is

low during the 16th falling SCLK edge, DOUT returns to

high impedance on the next rising edge of CNVST or

SCLK, enabling the serial interface to be shared by multi-

ple devices. If CNVST returns high after the 14th, but

before the 16th SCLK rising edge, DOUT remains active

so continuous conversions can be sustained. The high-

est throughput is achieved when performing continuous

conversions. Figure 10 illustrates a conversion using a

typical serial interface.

Connection to

Standard Interfaces

The MAX1077/MAX1079 serial interface is fully compati-

ble with SPI/QSPI and MICROWIRE (see Figure 11). If a

serial interface is available, set the CPU’s serial interface

in master mode so the CPU generates the serial clock.

Choose a clock frequency up to 24MHz.

SPI and MICROWIRE

When using SPI or MICROWIRE, the MAX1077/MAX1079

are compatible with all four modes programmed with the

CPHA and CPOL bits in the SPI or MICROWIRE control

register. Conversion begins with a CNVST falling edge.

DOUT goes low, indicating a conversion is in progress.

Two consecutive 1-byte reads are required to get the full

10 bits from the ADC. DOUT transitions on SCLK rising

1.5Msps, Single-Supply, Low-Power, True-

Differential, 10-Bit ADCs with Internal Reference

______________________________________________________________________________________

11

OUTPUT CODE

FULL-SCALE

TRANSITION

111...111

12

3

0

FS

FS - 3/2 LSB

DIFFERENTIAL INPUT

VOLTAGE (LSB)

1 LSB =

1024

111...110

111...101

000...011

000...010

000...001

000...000

ZS = 0

Figure 8. Unipolar Transfer Function (MAX1077 Only)

OUTPUT CODE

FULL-SCALE

TRANSITION

FS

0

-FS

FS - 3/2 LSB

DIFFERENTIAL INPUT

VOLTAGE (LSB)

011...111

011...110

000...010

000...001

000...000

111...111

111...110

111...101

100...001

100...000

1 LSB =

1024

FS =

2

- FS =

2

ZS = 0

Figure 9. Bipolar Transfer Function (MAX1079 Only)