2x4-Channel, Simultaneous-Sampling
12-Bit ADCs
MAX115/MAX116
HOLD
R1
BUFFER
CH_A
R2
S1A
C
IN
R3
S3A
MUX
R1
S1B
CH_B
R2
S2B
S2A
HOLD
C
HOLD
7pF
TRACK
FROM MICROSEQUENCER
TRACK
C
IN
R3
S3B
REFOUT
DAC
MAX115
MAX116
MAX115:
R1 =
∞,
R2 = R3 = 5kΩ
MAX116:
R1 = R2 = 5kΩ, R3 =
∞
SAR
Figure 3. Equivalent Input Circuit
The conversion timing and control sequences are
derived from either an internal clock or an external
clock, the
CONVST
signal, and the programmed mode.
The T/H amplifiers hold the input voltages at the
CONVST
rising edge. Additional
CONVST
pulses are
ignored until the last conversion for the sample is com-
plete. An on-board sequencer converts one to four
channels per
CONVST
pulse. In the default mode, one
T/H output (CH1A) is converted. An interrupt signal
(INT) is provided after the last conversion is complete.
Convert two to four channels by reprogramming the
MAX115/MAX116 through the bidirectional parallel
interface. Once programmed, the MAX115/MAX116
continues to convert the specified number of channels
per
CONVST
pulse until they are reprogrammed. The
channels are converted sequentially, beginning with
CH1. The
INT
signal always follows the end of the last
conversion in a conversion sequence. The ADC con-
verts each assigned channel in 2µs and stores the
result in an internal 4 x 12-bit memory.
At the end of the last conversion,
INT
goes low and the
T/H amplifiers begin to track the inputs again. The data
can be accessed by applying successive pulses to the
RD
pin. Successive reads access data words sequen-
8
tially. The memory is not random-access and data from
CH1 is always read first. After performing four consecu-
tive reads or initiating a new conversion, the address
pointer selects CH1 again. Additional read pulses cycle
through the data words.
CS
can be held low during
successive reads.
Input Bandwidth
The T/H’s input tracking circuitry has a 10MHz small-
signal bandwidth, so it is possible to digitize high-
speed transient events and measure periodic signals
with bandwidths exceeding the ADC’s sampling rate by
using undersampling techniques. To avoid high-
frequency signals being aliased into the frequency
band of interest, anti-alias filtering is recommended.
Analog Input Range and Input Protection
The MAX115’s input range is ±5V, and the MAX116’s
input range is ±2.5V. The input resistance for the
MAX115 is 10kΩ (typ), and the input resistance for the
MAX116 is 1MΩ (typ). An input protection structure
allows input voltages to ±17V without harming the IC.
This protection is also active in shutdown mode.
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