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參數資料
| 型號： | 7805ALPRPFS |
| 廠商： | MAXWELL TECHNOLOGIES |
| 元件分類： | ADC |
| 英文描述： | 1-CH 16-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, DFP28 |
| 封裝： | RAD-PAK, LDFP-28 |
| 文件頁數： | 34/34頁 |
| 文件大?。?/td> | 605K |
| 代理商： | 7805ALPRPFS |
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Memory
PRELIMINARY
9
All data sheets are subject to change without notice
2001 Maxwell Technologies
All rights reserved.
16-Bit Latchup Protected ADC
7805ALP
12.19.01 Rev 6
1000583
Differences Between the7805A and the ADS7805
Because the 7805A uses the ADS7805 die to perform the analog to digital conversion function its operation and per-
formance is very similar to the ADS7805 packaged part from Burr-Brown. In general the operation and application will
be the same for both parts. There are two primary differences: the operation of the supply pins and the operation of the
BYTE and STATUS pins.
The ADS7805 provides separate analog and digital supply pins. The 7805A provides a single supply input V
S pin in
place of the V
DIG pin which powers both the analog and digital circuitry through the LPT current sensor and power
switch. The V
S power supply should be treated as an analog supply and isolated from noise on the system digital
power supply. The low side of the power switch connects to the ADS7805 die power pads and to the package DEC-
PLNG pin which replaces the VANA pin. The DECPLNG pin allows low ESR ceramic capacitors to directly decouple
the ADS7805 die. CAUTION: The DECPLNG pin must not be connected to the power supply since this will defeat the
LPT power switch and could result in latchup of the device during operation in a radiation environment. Electrolytic
capacitors should not be connected to the DECPLNG pin because the large capacitance will increase the recovery
time of the 7805A.
The primary functional difference between the ADS7805 and the 7805A is that the BYTE signal of the ADS7805 is
internally grounded and the pin function is replaced by the STATUS output. Grounding the BYTE signal permanently
assigns the data output signal bits 15:0 as shown in the 7805A pinout diagram where bit15 is the MSB and bit 0 is the
LSB.
A high level STATUS signal indicates that a single event induced latchup current was detected by the LPT circuitry
causing power to be removed from the protected device. CAUTION: During the time that power is removed from the
protected device, it is critical that external circuitry driving the device I/O pins does not backdrive the device supply.
Backdriving the supply could contribute to an extended or even a permanent latchup condition.
In order to prevent backdriving the supply, the STATUS signal should be used in the system to tri-state or gate external
I/O drive circuits to a low state. Similarly, if the data outputs are connected to a bus with other bus driver circuits, all
external data bus drivers must be tri-stated and individual pull up resistors to the supply voltage (if used on the data
bus) must not be less than 10 K
typical to assure proper single event effect recovery. Tri-stating of inputs should
occur within 100 nsec after the rise of the status pin. The BYTE signal can be made available in place of the STATUS
signal at customer request.
STATUS can also be used to generate an input to the system data processor indicating that an LPT cycle has
occurred, and the protected device output accuracy may not be met until after the respective recovery time to the
event. The STATUS signal is generated from an advanced CMOS logic gate output. This output may not exhibit a
monotonic falltime and may even oscillate briefly while power is being restored to the protected device and the decou-
pling capacitance is charged. Loading on the STATUS output should be minimized because this signal is used inter-
nally by the 7805A. It is recommended that load current not exceed 2 mA and load capacitance be kept well below
1000 pF.
A summary of the pin differences between the ADS7805 and 7805A is provided below.
TABLE 16. PIN DIFFERENCES
PIN NUMBER
ADS7805
7805A
PIN DIFFERENCE DESCRIPTION
23
BYTE
STATUS
A high level STATUS signal indicates that power is removed from the ADS7805 die.
I/O pins must not be driven high while this signal is active. The BYTE signal of the
ADS7805 die is internally grounded but can also be made available in place of the
STATUS pin at customer request.
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