AD7477ARTZ-REEL7 Analog Devices Inc, AD7477ARTZ-REEL7 Datasheet - Page 15

• Manufacturer Part Number: AD7477ARTZ-REEL7
• Description: IC,A/D CONVERTER,SINGLE,10-BIT,CMOS,TSOP,6PIN
• Manufacturer: Analog Devices Inc

Specifications of AD7477ARTZ-REEL7

• Number Of Bits: 10
• Sampling Rate (per Second): 1M
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 17.5mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7477CBZ - BOARD EVALUATION FOR AD7477
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

TYPICAL CONNECTION DIAGRAM
Figure 7 shows a typical connection diagram for the AD7476A/
AD7477A/AD7478A. V
such, V
input range of 0 V to V
16-bit word with four leading zeros followed by the MSB of the
12-bit, 10-bit, or 8-bit result. The 10-bit result from the AD7477A
will be followed by two trailing zeros, and the 8-bit result from
the AD7478A will be followed by four trailing zeros.
Alternatively, because the supply current required by the AD7476A/
AD7477A/AD7478A is so low, a precision reference can be used
as the supply source to the AD7476A/AD7477A/AD7478A. A
REF19x voltage reference (REF195 for 5 V or REF193 for 3 V)
can be used to supply the required voltage to the ADC (see Figure 7).
This configuration is especially useful if the power supply is
quite noisy or if the system supply voltages are at some value
other than 5 V or 3 V (e.g., 15 V). The REF19x will output a
steady voltage to the AD7476A/AD7477A/AD7478A. If the low
dropout REF193 is used, the current it needs to supply to the
AD7476A/AD7477A/AD7478A is typically 1.2 mA. When
the ADC is converting at a rate of 1 MSPS, the REF193 will
need to supply a maximum of 1.7 mA to the AD7476A/
AD7477A/AD7478A. The load regulation of the REF193 is typi-
cally 10 ppm/mA (V
(51 µV) for the 1.7 mA drawn from it. This corresponds to a
0.069 LSB error for the AD7476A with V
REF193, a 0.017 LSB error for the AD7477A, and a 0.0043 LSB
error for the AD7478A. For applications where power consumption
is of concern, the power-down mode of the ADC and the sleep
mode of the REF19x reference should be used to improve
power performance. See the Modes of Operation section.
REV. C
680nF
0V TO V
INPUT
Figure 7. REF193 as Power Supply to AD7476A/
AD7477A/AD7478A
DD
DD
1.2mA
should be well decoupled. This provides an analog
V
GND
V
IN
DD
0.1 F
AD7476A/
AD7477A/
AD7478A
S
= 5 V), which results in an error of 17 ppm
DD
TANT
REF
1 F
3V
. The conversion result is output in a
is taken internally from V
SDATA
SCLK
CS
REF193
10 F
INTERFACE
SERIAL
DD
= 3 V from the
0.1 F
DD
5V
SUPPLY
C/ P
and, as
–15–
Table I provides some typical performance data with various
references used as a V
room temperature under the same setup conditions.
Analog Input
Figure 8 shows an equivalent circuit of the analog input structure
of the AD7476A/AD7477A/AD7478A. The two diodes, D1 and
D2, provide ESD protection for the analog input. Care must be
taken to ensure that the analog input signal never exceeds the
supply rails by more than 300 mV. This will cause these diodes
to become forward-biased and start conducting current into the
substrate. The maximum current these diodes can conduct
without causing irreversible damage to the part is 10 mA. The
capacitor C1 in Figure 8 is typically about 6 pF and can primarily
be attributed to pin capacitance. The resistor R1 is a lumped
component made up of the on resistance of a switch. This resistor
is typically about 100 Ω. The capacitor C2 is the ADC sampling
capacitor and has a capacitance of 20 pF typically. For ac applica-
tions, removing high frequency components from the analog input
signal is recommended by use of a band-pass filter on the relevant
analog input pin. In applications where harmonic distortion and
signal-to-noise ratio are critical, the analog input should be driven
from a low impedance source. Large source impedances will
significantly affect the ac performance of the ADC. This may
necessitate the use of an input buffer amplifier. The choice of
the op amp will be a function of the particular application.
Table I. AD7476A Typical Performance for Various
Voltage References IC
Reference Tied
to V
AD780 @ 3 V
REF193
AD780 @ 2.5 V
REF192
REF43
Figure 8. Equivalent Analog Input Circuit
DD
V
IN
AD7476A/AD7477A/AD7478A
6pF
C1
DD
V
CONVERSION PHASE – SWITCH OPEN
TRACK PHASE – SWITCH CLOSED
DD
D1
D2
source for a 100 kHz input tone at
AD7476A SNR Performance
(dB)
72.65
72.35
72.5
72.2
72.6
R1
20pF
C2