AD8557ARZ Analog Devices Inc, AD8557ARZ Datasheet - Page 18

• Manufacturer Part Number: AD8557ARZ
• Description: IC AMP CHOPPER 2MHZ 55MA 8SOIC
• Manufacturer: Analog Devices Inc
• Series: DigiTrim®r

Specifications of AD8557ARZ

• Amplifier Type: Chopper (Zero-Drift)
• Number Of Circuits: 1
• Gain Bandwidth Product: 2MHz
• Current - Input Bias: 18nA
• Voltage - Input Offset: 2µV
• Current - Supply: 1.8mA
• Current - Output / Channel: 55mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• No. Of Amplifiers: 1
• Input Offset Voltage: 12µV
• Gain Db Min: 28dB
• Bandwidth: 2MHz
• Amplifier Output: Single Ended / Differential
• Cmrr: 112dB
• Supply Voltage Range: 2.7V To 5.5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• -3db Bandwidth: -
• Slew Rate: -

Simulation Mode
The simulation mode allows any parameter to be temporarily
changed. These changes are retained until the simulated value is
reprogrammed, the power is removed, or the master fuse is
blown. Parameters are simulated by setting Field 1 to 01,
selecting the desired parameter in Field 2, and selecting the
desired value for the parameter in Field 4. Note that a value of
11 for Field 2 is ignored during the simulation mode. Examples
of temporary settings follow:
•
•
•
Programming Mode
Intact fuses give a bit value of 0. Bits with a desired value of 1
need to have the associated fuse blown. Because a relatively
large current is needed to blow a fuse, only one fuse can be
reliably blown at a time. Thus, a given parameter value may
need several 38-bit words to allow reliable programming.
A 5.75 V (±0.25 V) supply is required when blowing fuses to
minimize the on resistance of the internal MOS switches that
blow the fuse. The power supply voltage must not exceed the
absolute maximum rating and must be able to deliver 250 mA
of current.
At least 10 μF (tantalum type) of decoupling capacitance is
needed across the power pins of the device during program-
ming. The capacitance can be on the programming apparatus as
long as it is within 2 inches of the device being programmed.
An additional 0.1 μF (ceramic type) in parallel with the 10 μ F is
recommended within ½ inch of the device being programmed.
A minimum period of 1 ms should be allowed for each fuse to
blow. There is no need to measure the supply current during
programming.
The best way to verify correct programming is to use the read
mode to read back the programmed values. Then, remeasure
the gain and offset to verify these values. Programmed fuses
have no effect on the gain and output offset until the master
fuse is blown. After blowing the master fuse, the gain and
output offset are determined solely by the blown fuses, and the
simulation mode is permanently deactivated.
AD8557
Setting the second stage gain code (Parameter 00) to 011
and the second stage gain to 40 produces:
1000 0000 0001 01 00 10 0000 0011 0111 1111 1110
Setting the first stage gain code (Parameter 01) to 000 1011
and the first stage gain to 4.166 produces:
1000 0000 0001 01 01 10 0000 1011 0111 1111 1110
A first stage gain of 2.954 with a second stage gain of 40
gives a total gain of 118.16. This gain has a maximum
tolerance of 2.5%.
Set the output offset code (Parameter 10) to 0100 0000
and the output offset to 1.260 V when VDD = 5 V and
VSS = 0 V. This output offset has a maximum tolerance
of 0.8%:
1000 0000 0001 01 10 10 0100 0000 0111 1111 1110
Rev. B | Page 18 of 24
Parameters are programmed by setting Field 1 to 10, selecting
the desired parameter in Field 2, and selecting a single bit with
the value 1 in Field 4.
As an example, suppose the user wants to permanently set the
second stage gain to 40. Parameter 00 needs to have the value
0000 0011 assigned. Two bits have the value 1, so two fuses need
to be blown. Because only one fuse can be blown at a time, this
code can be used to blow one fuse:
1000 0000 0001 10 00 10 0000 0010 0111 1111 1110
The MOS switch that blows the fuse closes when the complete
packet is recognized, and opens when the start-of-packet,
dummy, or end-of-packet fields are no longer valid. After 1 ms,
this second code is entered to blow the second fuse:
1000 0000 0001 10 00 10 0000 0001 0111 1111 1110
To permanently set the first stage gain to a nominal value of
2.954, Parameter 01 needs to have the value 000 1011 assigned.
Three fuses need to be blown, and the following codes are used,
with a 1 ms delay after each code:
1000 0000 0001 10 01 10 0000 1000 0111 1111 1110
1000 0000 0001 10 01 10 0000 0010 0111 1111 1110
1000 0000 0001 10 01 10 0000 0001 0111 1111 1110
To permanently set the output offset to a nominal value of
1.260 V when VDD = 5 V and VSS = 0 V, Parameter 10 needs
to have the value 0100 0000 assigned. If one fuse needs to be
blown, use the following code:
1000 0000 0001 10 10 10 0100 0000 0111 1111 1110
Finally, to blow the master fuse to deactivate the simulation
mode and prevent further programming, use code:
1000 0000 0001 10 11 10 0000 0001 0111 1111 1110
There are a total of 20 programmable fuses. Because each fuse
requires 1 ms to blow, and each serial word can be loaded in
2.3 ms, the maximum time needed to program the fuses can be
as low as 66 ms.
Read Mode
The values stored by the polysilicon fuses can be sent to the
DIGOUT pin to verify correct programming. Normally, the
DIGOUT pin is only connected to the second gain stage output.
During read mode, however, the 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
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 DIGOUT pin. Pulses at DIGIN shift out the shift register
contents to the 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
DIGOUT from the shift register and terminates the read mode.