Rainbow Electronics MAX111 - Manual (Page 9)

MAX110/MAX111
Low-Cost, 2-Channel, ±14-Bit Serial ADCs
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_______________Detailed Description
The MAX110/MAX111 ADC converts low-frequency
analog signals to a 16-bit serial digital output (14 data
bits, a sign bit, and an overrange bit) using a first-order
sigma-delta loop (Figure 1). The differential input volt-
age is internally connected to a precision voltage-to-
current converter. The resulting current is integrated
and applied to a comparator. The comparator output
then drives an up/down counter and a 1-bit DAC. When
the DAC output is fed back to the integrator input, the
sigma-delta loop is completed.
During a conversion, the comparator output is a V
REF-
to V
REF+
square wave; its duty cycle is proportional to
the magnitude of the differential input voltage applied
to the ADC. The up/down counter clocks data in from
the comparator at the oversampling clock rate and
averages the pulse-width-modulated (PWM) square
wave to produce the conversion result. A 16-bit static
shift register stores the result at the end of the conver-
sion. Figure 2 shows the ADC waveforms for a differen-
tial analog input equal to 1/2 (V
REF+ - V REF- ). The
resulting comparator and 1-bit DAC outputs are high
for seven cycles and low for three cycles of the over-
sampling clock.
Since the analog input signal is integrated over many
clock cycles, much of the signal and quantization noise
is attenuated. The more clock cycles allowed during
each conversion, the greater the noise attenuation (see
Programming Conversion Time ).
______________________________________________________________Pin Description
Clock Input / RC Oscillator Output. TTL/CMOS-compatible oversampling clock input
when RCSEL = GND. Connects to the internal RC oscillator when RCSEL = V
DD
. XCLK
must be connected to V
DD
or GND through a resistor (1M
Ω
or less) when RC OSC
mode is selected.
XCLK 8
Serial Clock Input. TTL/CMOS-compatible clock input for serial-interface data I/O. SCLK 9
Busy Output. Goes low at conversion start, and returns high at end of conversion. BUSY 10
Positive Power-Supply Input—connect to +5V V DD 6
RC Select Input. Connect to GND to select external clock mode. Connect to V
DD
to
select RC OSC mode. XCLK must be connected to V
DD
or GND through a resistor
(1M Ω or less) when RC OSC mode is selected.
RCSEL 7
Positive Reference Input REF+ 3
Negative Reference Input REF- 2
Channel 1 Positive Analog Input IN1+ 1
FUNCTION NAME
SSOP
6
7
8
4
5
3
2
PIN
1
DIP/SO
Chip-Select Input. Pull this input low to perform a control-word-write/data-read opera-
tion. A conversion begins when CS returns high, provided NO-OP is a 1. See the sec-
tion
Using the MAX110/MAX111 with SPI, QSPI, and MICROWIRE Serial Interfaces.
CS 11 9
Serial Data Output. High-impedance when CS is high. DOUT 12 10
Serial Data Input. See Control Register section. DIN 13 11
Digital Ground GND 16 12
MAX110 Negative Power-Supply Input—connect to -5V V SS
Channel 2 Negative Analog Input IN2- 18 14
Channel 2 Positive Analog Input IN2+ 19 15
Channel 1 Negative Analog Input IN1- 20 16
No Connect—there is no internal connection to this pin N.C. 4, 5, 14, 15 —
MAX111 Analog Ground AGND
17 13