ADC101S101EVAL National Semiconductor, ADC101S101EVAL Datasheet - Page 14

• Manufacturer Part Number: ADC101S101EVAL
• Description: BOARD EVALUATION FOR ADC101S101
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of ADC101S101EVAL

• Number Of Adc's: 1
• Number Of Bits: 10
• Sampling Rate (per Second): 1M
• Data Interface: Serial
• Inputs Per Adc: 1 Single Ended
• Input Range: 0 ~ 5.25 V
• Power (typ) @ Conditions: 10mW @ 1MSPS
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: ADC101S101
• Lead Free Status / RoHS Status: Not applicable / Not applicable

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To exit shutdown mode, bring CS back low. Upon bringing
CS low, the ADC will begin powering up (power-up time is
specified in the Timing Specifications table). This power-up
delay results in the first conversion result being unusable. The
second conversion performed after power-up, however, is
valid, as shown in Figure 9.
If CS is brought back high before the 10th falling edge of
SCLK, the device will return to shutdown mode. This is done
to avoid accidentally entering normal mode as a result of
noise on the CS line. To exit shutdown mode and remain in
normal mode, CS must be kept low until after the 10th falling
edge of SCLK. The ADC will be fully powered-up after 16
SCLK cycles.
8.0 POWER MANAGEMENT
The ADC takes time to power-up, either after first applying
V
This corresponds to one "dummy" conversion for any SCLK
frequency within the specifications in this document. After this
first dummy conversion, the ADC will perform conversions
properly. Note that the t
tween the first dummy conversion and the second valid con-
version.
When the V
in either of the two modes: normal or shutdown. As such, one
dummy conversion should be performed after start-up, as de-
scribed in the previous paragraph. The part may then be
placed into either normal mode or the shutdown mode, as
described in Sections 7.1 and 7.2.
When the ADC is operated continuously in normal mode, the
maximum guaranteed throughput is f
specified f
sumption by running f
performing fewer conversions per unit time, raising the ADC
A
, or after returning to normal mode from shutdown mode.
SCLK
A
supply is first applied, the ADC may power up
. Throughput may be traded for power con-
SCLK
QUIET
at its maximum specified rate and
time must still be included be-
SCLK
/ 20 at the maximum
FIGURE 8. Entering Shutdown Mode
FIGURE 9. Entering Normal Mode
14
CS line after the 10th and before the 15th fall of SCLK of each
conversion. A plot of typical power consumption versus
throughput is shown in the Typical Performance Curves sec-
tion. To calculate the power consumption for a given through-
put, multiply the fraction of time spent in the normal mode by
the normal mode power consumption and add the fraction of
time spent in shutdown mode multiplied by the shutdown
mode power consumption. Note that the curve of power con-
sumption vs. throughput is essentially linear. This is because
the power consumption in the shutdown mode is so small that
it can be ignored for all practical purposes.
9.0 POWER SUPPLY NOISE CONSIDERATIONS
The charging of any output load capacitance requires current
from the power supply, V
the supply to charge the output capacitance will cause voltage
variations on the supply. If these variations are large enough,
they could degrade SNR and SINAD performance of the ADC.
Furthermore, discharging the output capacitance when the
digital output goes from a logic high to a logic low will dump
current into the die substrate, which is resistive. Load dis-
charge currents will cause "ground bounce" noise in the sub-
strate that will degrade noise performance if that current is
large enough. The larger the output capacitance, the more
current flows through the die substrate and the greater is the
noise coupled into the analog channel, degrading noise per-
formance.
To keep noise out of the power supply, keep the output load
capacitance as small as practical. It is good practice to use a
100Ω series resistor at the ADC output, located as close to
the ADC output pin as practical. This will limit the charge and
discharge current of the output capacitance and improve
noise performance.
A
. The current pulses required from
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