MAX145ACUA+ Maxim Integrated Products, MAX145ACUA+ Datasheet - Page 8

• Manufacturer Part Number: MAX145ACUA+
• Description: IC ADC 12BIT 108KSPS 8-UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX145ACUA+

• Number Of Bits: 12
• Sampling Rate (per Second): 108k
• Data Interface: MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 330mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The capacitive digital-to-analog converter (DAC)
adjusts during the remainder of the conversion cycle
to restore node ZERO to 0V within the limits of 12-bit
resolution. This action is equivalent to transferring a
16pF · [(V
ry-weighted capacitive DAC, which in turn forms a digi-
tal representation of the analog input signal.
The ADC’s T/H stage enters its tracking mode on the
falling edge of CS/SHDN. For the MAX144 (single-
ended inputs), IN- is connected to GND and the con-
verter samples the positive (“+”) input. For the MAX145
(pseudo-differential inputs), IN- connects to the nega-
tive input (“-”) and the difference of [(V
sampled. At the end of the conversion, the positive
input connects back to IN+ and C
input signal.
The time required for the T/H stage to acquire an input
signal is a function of how fast its input capacitance is
charged. If the input signal’s source impedance is high,
the acquisition time lengthens, and more time must be
allowed between conversions. The acquisition time,
t
the signal, and is also the minimum time required for
the signal to be acquired. Calculate this with the follow-
ing equation:
where R
R
input capacitance of the ADC. Source impedances
below 1kΩ have no significant impact on the AC perfor-
mance of the MAX144/MAX145.
+2.7V, Low-Power, 2-Channel, 108ksps,
Serial 12-Bit ADCs in 8-Pin µMAX
Figure 4. Analog Input with Anti-Aliasing Filter Structure
8
ACQ
IN
_______________________________________________________________________________________
(9kΩ) is the input resistance, and C
, is the maximum time the device takes to acquire
**USED TO ATTENUATE SWITCHED-CAPACITOR FILTER CLOCK NOISE
S
f
C
IN+
is the source impedance of the input signal,
= 15kHz
) - (V
2
t
ACQ
IN
IN-
COM
)] charge from C
0.01 F
1
= 9(R
MAX7410
MAX7414
V
OS
DD
S
4
6
+ R
GND
IN
SHDN
3
Track/Hold (T/H)
HOLD
)C
OUT
CLK
IN
HOLD
7
5
8
IN
IN+
charges to the
(16pF) is the
) - (V
OSCILLATOR
to the bina-
1.5MHz
470 **
IN-
V
DD
)] is
0.1 F
0.01 F**
Higher source impedances can be used if a 0.01µF
capacitor is connected to the individual analog inputs.
Together with the input impedance, this capacitor
forms an RC filter, limiting the ADC’s signal bandwidth.
The MAX144/MAX145 T/H stage offers a 2.25MHz
small-signal and a 1MHz full-power bandwidth, which
make it possible to use the parts for digitizing high-
speed transients and measuring periodic signals with
bandwidths exceeding the ADCs sampling rate by
using undersampling techniques. To avoid high-fre-
quency signals being aliased into the frequency band
of interest, anti-alias filtering is recommended. Most
aliasing problems can be fixed easily with an external
resistor and a capacitor. However, if DC precision is
required, it is usually best to choose a continuous or
switched-capacitor filter, such as the MAX7410/
MAX7414 (Figure 4). Their Butterworth characteristic
generally provides the best compromise (with regard to
rolloff and attenuation) in filter configurations, is easy to
design, and provides a maximally flat passband response.
Internal protection diodes, which clamp the analog input
to V
within GND - 300mV to V
However, for accurate conversions, both inputs must not
exceed V
If an off-channel analog input voltage exceeds the
supplies, limit the input current to 4mA.
DD
and GND, allow each input channel to swing
2
3
8
DD
CH0
CH1
SCLK
+ 50mV or be less than GND - 50mV.
MAX144
GND
V
DD
1
4
CS/SHDN
Analog Input Protection
DD
DOUT
REF
+ 300mV without damage.
5
7
6
Input Bandwidth
EXTERNAL
REFERENCE
P/ C