AD8556ARZ Analog Devices Inc, AD8556ARZ Datasheet - Page 22

• Manufacturer Part Number: AD8556ARZ
• Description: IC AMP CHOPPER 2MHZ 10MA 8SOIC
• Manufacturer: Analog Devices Inc
• Series: DigiTrim®r
• Type: Instrumentation Amplifierr

Specifications of AD8556ARZ

• Operating Temperature: -40°C ~ 140°C
• Amplifier Type: Chopper (Zero-Drift)
• Number Of Circuits: 1
• Slew Rate: 1.2 V/µs
• Gain Bandwidth Product: 2MHz
• Current - Input Bias: 49nA
• Voltage - Input Offset: 2µV
• Current - Supply: 2mA
• Current - Output / Channel: 10mA
• Voltage - Supply, Single/dual (±): 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• No. Of Amplifiers: 1
• Bandwidth: 700kHz
• Rail To Rail I/o Type: Rail-Rail I/O
• No. Of Channels: 1
• Supply Voltage Range: 2.7V To 5.5V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Number Of Channels: 1
• Number Of Elements: 5
• Power Supply Requirement: Single
• Common Mode Rejection Ratio: 80dB
• Unity Gain Bandwidth Product (typ): 8MHz
• Single Supply Voltage (typ): 5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Rejection Ratio: 109dB
• Rail/rail I/o Type: Rail to Rail Input/Output
• Single Supply Voltage (min): 4.5V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 140C
• Operating Temperature Classification: Automotive
• Mounting: Surface Mount
• Pin Count: 8
• Package Type: SOIC N
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• -3db Bandwidth: -
• Lead Free Status / Rohs Status: Compliant

AD8556
Read Mode
The values stored by the polysilicon fuses can be sent to the
FILT/DIGOUT pin to verify correct programming. Normally,
the FILT/DIGOUT pin is only connected to the second gain stage
output via RF. During read mode, however, the FILT/DIGOUT pin
is also connected to the output of a shift register to allow the
polysilicon fuse contents to be read. Because VOUT is a buffered
version of FILT/DIGOUT, VOUT also outputs a digital signal
during read mode.
Read mode is entered by setting Field 1 to 11 and selecting the
desired parameter in Field 2. Field 4 is ignored. The parameter
value, stored in the polysilicon fuses, is loaded into an internal
shift register, and the MSB of the shift register is connected to
the FILT/DIGOUT pin. Pulses at DIGIN shift out the shift
register contents to the FILT/DIGOUT pin, allowing the 8‒bit
parameter value to be read after seven additional pulses; shifting
occurs on the falling edge of DIGIN. An eighth pulse at DIGIN
disconnects FILT/DIGOUT from the shift register and terminates
the read mode. 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 FILT/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 FILT/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 AD8556 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, which is
much lower than 1.5 V; therefore, 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; therefore, Logic 1 is output from the OTP cell.
Rev. A | Page 22 of 28
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.
Therefore, 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
developed across the fuse would then change from 1.5 V to
0.38 V, and the output of the OTP would be Logic 0 instead of
the expected Logic 1 from a blown fuse. Fuses blown correctly
would still output Logic 1. In this way, fuses blown incorrectly
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 AD8556
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.
2.
When programming the AD8556, the temperature of the
device must be between 10°C and 40°C.
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 5, Table 6, 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.