AD9204BCPZ-40 Analog Devices Inc, AD9204BCPZ-40 Datasheet - Page 22

• Manufacturer Part Number: AD9204BCPZ-40
• Description: 10 Bit 40 Msps Dual Low Power ADC
• Manufacturer: Analog Devices Inc

Specifications of AD9204BCPZ-40

• Number Of Bits: 10
• Sampling Rate (per Second): 40M
• Data Interface: Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 97.7mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 64-LFCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9204
VOLTAGE REFERENCE
A stable and accurate 1.0 V voltage reference is built into the
AD9204. The VREF can be configured using either the internal
1.0 V reference or an externally applied 1.0 V reference voltage.
The various reference modes are summarized in the sections that
follow. The Reference Decoupling section describes the best
practices PCB layout of the reference.
Internal Reference Connection
A comparator within the AD9204 detects the potential at the
SENSE pin and configures the reference into two possible
modes, which are summarized in Table 10. If SENSE is grounded,
the reference amplifier switch is connected to the internal resistor
divider (see Figure 46), setting VREF to 1.0 V.
Table 10. Reference Configuration Summary
Selected Mode
Fixed Internal Reference
Fixed External Reference
Table 11. Scaled Differential Span Summary
Selected Mode
Fixed Internal or External Reference
Fixed Internal or External Reference
Fixed Internal or External Reference
Fixed Internal or External Reference
Fixed Internal or External Reference
1.0µF
Figure 46. Internal Reference Configuration
VIN+A/VIN+B
VIN–A/VIN–B
0.1µF
SENSE
VREF
SELECT
SENSE Voltage (V)
AGND to 0.2
AVDD
LOGIC
ADC
Resulting VREF (V)
1.0 (internal or external)
1.0 (internal or external)
1.0 (internal or external)
1.0 (internal or external)
1.0 (internal or external)
0.5V
CORE
ADC
Resulting VREF (V)
1.0 internal
1.0 applied to external VREF pin
Rev. 0 | Page 22 of 36
SPI Register 0x18 (Hex)
0xC0
0xC8
0xD0
0xD8
0xE0
In either internal or external reference mode, the maximum
input range of the ADC can be varied by configuring SPI
Address 0x18 as shown in Table 11, resulting in a selectable
differential span from 1 V p-p to 2 V p-p.
If the internal reference of the AD9204 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered. Figure 47 shows
how the internal reference voltage is affected by loading.
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
0
0
0.2
Figure 47. VREF Accuracy vs. Load Current
0.4
Resulting Differential Span (V p-p)
2.0
2.0
0.6
LOAD CURRENT (mA)
Resulting Differential Span (V p-p)
1.0
1.14
1.33
1.6
2.0
INTERNAL V
0.8
1.0
REF
1.2
= 0.993V
1.4
1.6
1.8
2
.0