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参数资料
| 型号： | AN-7820 |
| 厂商： | Fairchild Semiconductor Corporation |
| 元件分类： | 圆形连接器 |
| 英文描述： | Circular Connector; No. of Contacts:37; Series:MS27656; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Pin; Circular Shell Style:Wall Mount Receptacle; Insert Arrangement:15-35 RoHS Compliant: No |
| 中文描述： | 评价委员会 |
| 文件页数： | 2/17页 |
| 文件大小： | 206K |
| 代理商： | AN-7820 |
2
5/22/97
AN7820/24
POWER SUPPLIES
EB7820/24 requires four power supply sources: analog -
5.2 V (-A5.2 V), analog +5 V (+A5 V), digital - 5.2 V (- D5.2
V), and digital +5 V (+D5 V) . P1 is the power connector. (See
figure 2.) The recommended operating voltage range is
shown in table 1.
Table 1 - Recommended Power Supply Operating Range
Typ
PS
Min
Typ
Max
Current
60 mA
240 mA
15 mA
60 mA
-A5.2 V -4.95 V
+A5 V
-D5.2 V -4.95 V
+D5 V
-5.20 V
+5.00 V
-5.20 V
+5.00 V
- 5.45 V
+5.25 V
- 5.45 V
+5.25 V
+4.75 V
+4.75 V
Figure 2 - P1, Power Supply Connector’s Pin Assignment
FEMALE
TERMINAL
3
2
1
4
5
6
7
8
9
P1
(top view)
PIN#
1
2
3
4
5
6
7
8
9
PIN ASSIGNMENT
ANALOG - 5.2 V
ANALOG - 5.2 V RETURN # 1 (AGND)
ANALOG - 5.2 V RETURN # 2 (AGND)
ANALOG + 5V
ANALOG + 5 V RETURN (AGND)
DIGITAL - 5.2 V RETURN (DGND)
DIGITAL + 5 V
DIGITAL + 5 V RETURN (DGND)
DIGITAL - 5.2 V
The total power dissipation is typically 1.89 watts, including
the SPT7820 or SPT7824 (1.1 W typ).
POWER SUPPLY HOOK-UPS
Figure 3 - P1 Connector/Hook-Up
P1 POWER CONNECTOR
-5.2 V
+ 5 V
+ 5 V
- 5.2 V
2
3
1
4
5
6
9
7
8
+
-
+
-
+
-
+
-
POWER SUPPLIES AND GROUNDING
The SPT7820/24 requires two analog supply voltages: -
A5.2 V and +A5 V. The +A5 V supply is common to analog
VCC (pin 18 &25) and digital DVCC (pin 14 and 28). A ferrite
bead in series with each supply (RF1 and RF2) reduces the
transient noise injected into VCC. The bead (RF1 or RF2) to
SPT7820/24 connections should not be shared with any
other device. Bypass each power supply pin as closely as
possible to the device (0.1
μ
F to AGND for each VEE and
VCC pin and 0.01
μ
F to DGND for the DVCC pin).
AGND and DGND are isolated on the SPT7820 and SPT7824.
Both -A5.2 V and +A5 V are the analog supply sources. As
in most very high speed ADCs, grounding is critical. There-
fore, the ground plane technique is the most desirable for the
SPT7820/24. To accomplish this, split and tie together the
AGND and DGND ground planesonly at the device (SPT7820/
24) through an RF bead. The EB7820/24 is a four-layer
printed circuit board: the top signal, ground (AGND & DGND)
plane, power plane and the bottom signal. The two ground
planes are connected together at the device through a ferrite
bead (RF3). All three ferrite beads (RF1-3) are located close
to the ADC.
The analog input (pin 21) is physically sandwiched between
the reference taps. Carefully plan printed circuit board layout
to minimize any pick-up from VIN (high frequency) into the
references (VFT or VFB).
REFERENCE CIRCUIT
The SPT7820/24 requires the use of two voltage references:
VFT and VFB. VFT is the force for the top of the voltage
reference ladder (+2.5 V typ), and VFB (-2.5 V typ) is the force
for the bottom of the voltage reference ladder. Both voltages
are applied across an internal reference ladder resistance of
900
. In addition, there are three reference ladder taps:
VST, VRM and VSB. VST is the top of the reference ladder
tap (+2 V), VRM is the middle point (0.0 V typ), and VSB is the
bottom of the reference ladder tap (-2 V). The voltages seen
at VST and VSB are the expected full scale input voltages of
the device when VFT and VFB are driven to the recom-
mended voltages (+2.5 V and -2.5 V respectively). Use VST
and VSB to monitor the actual full scale input voltages (
±
2 V)
by adjusting VFT and VFB. These adjustments have some
interaction; repeat a few times as needed until VST and VSB
settle at the desired voltages. Do not drive VRM as is
commonly done with a standard flash ADC converter. When
not being used (VST, VRM & VSB), decouple with a 0.01
μ
F
chip capacitor (surface mounted) to AGND from each tap to
minimize high frequency noise injection.
Referring to figure 17, U2 is the + 2.5 V reference with
±
150 mV of adjustable range (R1 potentiometer). U3 (OP-
-07) is an inverting amplifier. Its tolerance is 5% with
±
300 mV
of adjustable range (R2 potentiometer). Fairchild recom-
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