参数资料
| 型号： | AD8557ARZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 11/24页 |
| 文件大小： | 0K |
| 描述： | IC AMP CHOPPER 2MHZ 55MA 8SOIC |
| 标准包装： | 98 |
| 系列： | DigiTrim® |
| 放大器类型： | 断路器（零漂移） |
| 电路数： | 1 |
| 增益带宽积： | 2MHz |
| 电流 - 输入偏压： | 18nA |
| 电压 - 输入偏移： | 2µV |
| 电流 - 电源： | 1.8mA |
| 电流 - 输出 / 通道： | 55mA |
| 电压 - 电源，单路/双路(±)： | 2.7 V ~ 5.5 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SO |
| 包装： | 管件 |
| 产品目录页面： | 771 (CN2011-ZH PDF) |
AD8557
Rev. C | Page 19 of 24
If a parameter value is less than eight bits long, the MSBs of the
shift register are padded with 0s.
For example, to read the second stage gain, this code is used:
1000 0000 0001 11 00 10 0000 0000 0111 1111 1110
Because the second stage gain parameter value is only three bits
long, the DIGOUT pin has a value of 0 when this code is
entered, and remains 0 during four additional pulses at DIGIN.
The fifth, sixth, and seventh pulses at DIGIN return the 3-bit
value at DIGOUT, the seventh pulse returns the LSB. An eighth
pulse at DIGIN terminates the read mode.
Sense Current
A sense current is sent across each polysilicon fuse to determine
whether it has been blown. When the voltage across the fuse is
less than approximately 1.5 V, the fuse is considered not blown,
and Logic 0 is output from the OTP cell. When the voltage
across the fuse is greater than approximately 1.5 V, the fuse is
considered blown, and Logic 1 is output.
When the AD8557 is manufactured, all fuses have a low
resistance. When a sense current is sent through the fuse, a
voltage less than 0.1 V is developed across the fuse. This is
much lower than 1.5 V, so Logic 0 is output from the OTP cell.
When a fuse is electrically blown, it should have a very high
resistance. When the sense current is applied to the blown fuse,
the voltage across the fuse should be larger than 1.5 V, so
Logic 1 is output from the OTP cell.
It is theoretically possible, though very unlikely, for a fuse to
be incompletely blown during programming, assuming the
required conditions are met. In this situation, the fuse could
have a medium resistance, neither low nor high, and a voltage of
approximately 1.5 V could be developed across the fuse. Thus,
the OTP cell could output Logic 0 or Logic 1, depending on
temperature, supply voltage, and other variables.
To detect this undesirable situation, the sense current can be
lowered by a factor of 4 using a specific code. The voltage devel-
oped across the fuse would then change from 1.5 V to 0.38 V,
and the output of the OTP would be a Logic 0 instead of the
expected Logic 1 from a blown fuse. Correctly blown fuses would
still output a Logic 1. In this way, incorrectly blown fuses can be
detected. Another specific code would return the sense current
to the normal (larger) value. The sense current cannot be
permanently programmed to the low value. When the AD8557
is powered up, the sense current defaults to the high value.
The low sense current code is
1000 0000 0001 00 00 10 XXXX XXX1 0111 1111 1110
The normal (high) sense current code is
1000 0000 0001 00 00 10 XXXX XXX0 0111 1111 1110
Programming Procedure
For reliable fuse programming, it is imperative to follow the
programming procedure requirements, especially the proper
supply voltage during programming:
1. When programming the AD8557, the temperature of the
device must be between 10°C to 40°C.
2. Set VDD and VSS to the desired values in the application.
Use simulation mode to test and determine the desired
codes for the second stage gain, first stage gain, and output
offset. The nominal values for these parameters are shown
in Table 6, Table 7, Equation 2, and Equation 3; use the
codes corresponding to these values as a starting point.
However, because actual parameter values for given codes
vary from device to device, some fine tuning is necessary
for the best possible accuracy.
One way to choose these values is to set the output offset to
an approximate value, such as Code 128 for midsupply, to
allow the required gain to be determined. Then, set the
second stage gain so the minimum first stage gain (Code 0)
gives a lower gain than required, and the maximum first
stage gain (Code 127) gives a higher gain than required.
After choosing the second stage gain, the first stage gain
can be chosen to fine tune the total gain. Finally, the output
offset can be adjusted to give the desired value. After
determining the desired codes for second stage gain, first
stage gain, and output offset, the device is ready for
permanent programming.
Note that once a programming attempt has been made for
any fuse, there should be no further attempt to blow that
fuse. If a fuse does not program to the expected state,
discard the unit. The expected incidence rate of attempted
but unblown fuses is very small when following the proper
programming procedure and conditions.
3. Set VSS to 0 V and VDD to 5.75 V (±0.25 V). Power
supplies should be capable of supplying 250 mA at the
required voltage and properly bypassed as described in the
Programming Mode section. Use program mode to
permanently enter the desired codes for the first stage gain,
second stage gain, and output offset. Blow the master fuse
to allow the AD8557 to read data from the fuses and to
prevent further programming.
4. Set VDD and VSS to the desired values in the application.
Use read mode with low sense current followed by high
sense current to verify programmed codes.
5. Measure gain and offset to verify correct functionality.
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