|
MAX1190 Datasheet, PDF (13/21 Pages) Maxim Integrated Products – Dual 10-Bit, 120Msps, 3.3V, Low-Power ADC with Internal Reference and Parallel Outputs | |||
|
◁ |
Dual 10-Bit, 120Msps, 3.3V, Low-Power ADC
with Internal Reference and Parallel Outputs
System Timing Requirements
Figure 3 depicts the relationship between the clock
input, analog input, and data output. The MAX1190
samples at the rising edge of the input clock. Output
data for channels A and B is valid on the next rising
edge of the input clock. The output data has an internal
latency of five clock cycles. Figure 3 also determines
the relationship between the input clock parameters
and the valid output data on channels A and B.
Digital Output Data (D0A/BâD9A/B), Output
Data Format Selection (T/B), Output
Enable (OE)
All digital outputs, D0AâD9A (channel A) and D0BâD9B
(channel B), are TTL/CMOS-logic compatible. There is
a five-clock-cycle latency between any particular sam-
ple and its corresponding output data. The output cod-
ing can be chosen to be either straight offset binary or
twoâs complement (Table 1) controlled by a single pin
(T/B). Pull T/B low to select offset binary and high to
activate twoâs complement output coding. The capaci-
tive load on digital outputs D0AâD9A and D0BâD9B
should be kept as low as possible (<15pF) to avoid
large digital currents that could feed back into the ana-
log portion of the MAX1190, thereby degrading its
dynamic performance. Using buffers on the digital out-
puts of the ADCs can further isolate the digital outputs
from heavy capacitive loads. To further improve the
dynamic performance of the MAX1190, small series
resistors (e.g., 100â¦) can be added to the digital output
paths, close to the MAX1190.
Figure 4 displays the timing relationship between out-
put enable and data output valid, as well as power-
down/wakeup and data output valid.
Power-Down (PD) and Sleep
(SLEEP) Modes
The MAX1190 offers two power-save modesâsleep
mode and full power-down mode. In sleep mode
(SLEEP = 1), only the reference bias circuit is active
OE
OUTPUT
D9AâD0A
tENABLE
HIGH-Z
tDISABLE
VALID DATA
HIGH-Z
OUTPUT
D9BâD0B
HIGH-Z
VALID DATA
HIGH-Z
Figure 4. Output Timing Diagram
(both ADCs are disabled), and current consumption is
reduced to 3mA.
To enter full power-down mode, pull PD high. With OE
simultaneously low, all outputs are latched at the last
value prior to the power down. Pulling OE high forces
the digital outputs into a high-impedance state.
Applications Information
Figure 5 depicts a typical application circuit containing
two single-ended to differential converters. The internal
reference provides a VDD/2 output voltage for level-
shifting purposes. The input is buffered and then split
to a voltage follower and inverter. One lowpass filter per
amplifier suppresses some of the wideband noise
associated with high-speed operational amplifiers. The
user can select the RISO and CIN values to optimize the
filter performance to suit a particular application. For
the application in Figure 5, a RISO of 50⦠is placed
before the capacitive load to prevent ringing and oscil-
lation. The 22pF CIN capacitor acts as a small filter
capacitor.
Table 1. MAX1190 Output Codes For Differential Inputs
DIFFERENTIAL INPUT
VOLTAGE*
VREF Ã 512/512
VREF Ã 1/512
0
-VREF Ã 1/512
-VREF Ã 511/512
-VREF Ã 512/512
*VREF = VREFP - VREFN
DIFFERENTIAL INPUT
+FULL SCALE - 1LSB
+1LSB
Bipolar Zero
-1LSB
-FULL SCALE + 1LSB
-FULL SCALE
STRAIGHT OFFSET BINARY
T/B = 0
11 1111 1111
10 0000 0001
10 0000 0000
01 1111 1111
00 0000 0001
00 0000 0000
TWOâS COMPLEMENT
T/B = 1
01 1111 1111
00 0000 0001
00 0000 0000
11 1111 1111
10 0000 0001
10 0000 0000
______________________________________________________________________________________ 13
|
▷ |