AD7910ARM-REEL AD [Analog Devices], AD7910ARM-REEL Datasheet - Page 10

• Manufacturer Part Number: AD7910ARM-REEL
• Description: 250 kSPS, 10-/12-Bit ADCs in 6-Lead SC70
• Manufacturer: AD [Analog Devices]

AD7910/AD7920
CIRCUIT INFORMATION
The AD7910/AD7920 are fast, micropower, 10-bit/12-bit,
single-supply A/D converters, respectively. The parts can be
operated from a 2.35 V to 5.25 V supply. When operated from
either a 5 V supply or a 3 V supply, the AD7910/AD7920 are
capable of throughput rates of 250 kSPS when provided with a
5 MHz clock.
The AD7910/AD7920 provide the user with an on-chip track-
and-hold, A/D converter, and a serial interface housed in a tiny
6-lead SC70 package or 8-lead MSOP package, which offers the
user considerable space saving advantages over alternative solu-
tions. The serial clock input accesses data from the part but also
provides the clock source for the successive-approximation A/D
converter. The analog input range is 0 V to V
reference is not required for the ADC and there is no reference
on-chip. The reference for the AD7910/AD7920 is derived from
the power supply and thus gives the widest dynamic input range.
The AD7910/AD7920 also feature a power-down option to
allow power saving between conversions. The power-down feature
is implemented across the standard serial interface, as described
in the Modes of Operation section.
TPC 6. THD vs. Analog Input Frequency for
Various Source Impedances
–0.2
–0.4
–0.6
–0.8
–1.0
–10
–20
–30
–40
–50
–60
–70
–80
–90
1.0
0.8
0.6
0.4
0.2
0
10
0
V
TEMP = 25 C
f
V
R
R
SAMPLE
TPC 5. AD7920 DNL Performance
DD
DD
IN
IN
512
= 10k
= 1k
= 2.35V
= 3.6V
= 250kSPS
1024
INPUT FREQUENCY (kHz)
R
IN
1536
= 130
CODE
2048
100
R
2560
IN
R
IN
= 13
= 0
3072
DD
. An external
3584
1000
4096
–10–
CONVERTER OPERATION
The AD7910/AD7920 is a successive-approximation analog-
to-digital converter based around a charge redistribution DAC.
Figures 4 and 5 show simplified schematics of the ADC.
Figure 4 shows the ADC during its acquisition phase. When
SW2 is closed and SW1 is in position A, the comparator is
held in a balanced condition, and the sampling capacitor
acquires the signal on V
V
IN
–65
–70
–75
–80
–85
–90
TPC 7. THD vs. Analog Input Frequency for
Various Supply Voltages
A
SW1
10
AGND
B
CAPACITOR
SAMPLING
Figure 4. ADC Acquisition Phase
V
DD
ACQUISITION
V
DD
= 5.25V
PHASE
V
= 4.75V
DD
/2
IN
INPUT FREQUENCY (kHz)
.
V
V
DD
DD
SW2
= 2.7V
= 2.35V
100
COMPARATOR
V
DD
= 3.6V
REDISTRIBUTION
CHARGE
CONTROL
DAC
LOGIC
1000
REV. B