AD5520 Analog Devices, AD5520 Datasheet - Page 12

• Manufacturer Part Number: AD5520
• Description: Per Pin Parametric Measurement Unit/Source Measure Unit
• Manufacturer: Analog Devices

AD5520
Current Ranges
A number of current ranges are possible with the AD5520. The
AM0, AM1, and AM2 pins are digital inputs used to establish
full-scale current range of the PMU.
AM0 AM1 AM2 Function
Low
High
Low
High
Low
High
Low
High
R
The AD5520 is designed so that the voltage drop across each of
the R
is flowing through them. To support other current ranges, these
sense resistor values may be changed. A force amplifier can
drive a maximum of 6 mA. It is not recommended to increase
the maximum current above the nominal range.
The two external current ranges use an external buffer to drive the
required current. Our example uses 40 mA and 160 mA ranges.
These ranges can be changed to suit user requirements for a high
current range.
Force Control Amplifier
The force control amplifier requires external capacitors connected
between the COMPOUTx and COMPINx pins. For stability
with large capacitance at the DUT, the largest capacitance value
(3000 pF) should be selected. The force control amplifier should
always contribute the dominant pole in the control loop. Set-
tling times will increase with larger capacitances. ACx inputs
select which external compensation capacitor is used.
Comparator Function and Strobing
The AD5520 has an on-board window comparator that pro-
vides two bits of useful information, DUT too low or too high.
CPSEL is the digital input that controls this function, selecting
whether it should compare to the voltage sense or the current
sense amplifier.
S
AC0
Low
High Low
Low
Selection
Table VI. AC0, AC1 Compensation Capacitor Selection
S
CPSEL
Low
High
resistors will be less than ±500 mV when maximum current
Low
Low
High
High
Low
Low
High
High
AC1
Low
High
Table VII. Comparator Function Select
Table V. Selection of Current Range
Low
Low
Low
Low
High Current Range MODE4 (External
High Current Range MODE5 (External
High Standby (same as STANDBY = High)
High Standby (same as STANDBY = High)
Function
Select External Compensation Capacitor 0
Select External Compensation Capacitor 1
Select External Compensation Capacitor 2
Function
Compare CPL, CPH to MEASVOUT
Compare CPL, CPH to MEASIOUT
Current Range MODE0 (up to 4 µA)
Current Range MODE1 (up to 40 µA)
Current Range MODE2 (up to 400 µA)
Current Range MODE3 (up to 4 mA)
Buffer Mode)
Buffer Mode)
–12–
After CPSEL has selected which amplifier output is of interest,
logic input CPCK is used to initiate comparator sampling and
update the logic outputs CPOH and CPOL, indicating if the
voltages at MEASIOUT or MEASVOUT have exceeded volt-
ages set at CPL or CPH (thus providing DUT too high or DUT
too low information). A rising edge on STB is required to clock
the CPOH and CPOL data out.
Clamp Function
Clamp circuitry is also included on chip, allowing the output of
the force amplifier to be clamped in the event of the voltage at
MEASIOUT and MEASVOUT exceeding CLL and CLH. The
clamp circuitry play their role in the event of a short or open
circuit. When in force current range, the voltage clamps protect
the DUT in the event of an open circuit. Likewise, when forcing
a voltage and a short circuit occurs, the current clamps will
protect the DUT in this case. The clamps also function to pro-
tect the DUT in the event of a transient voltage or current spike
that may occur when changing to a different operating mode or
when programming the device to a different current range.
The digital output flags, which indicate a clamp limit has been
hit, are CLHDETECT for the upper clamp and CLLDETECT
output for the lower clamp.
High Current Ranges
With the use of an external high current amplifier, two high
current ranges are possible. The current range values can be
selected as required in the application through appropriate
selection of the sense resistors connected between MEASI5H,
MEASI4H, and MEASIL. When one of these high current
ranges (MODE 4 or MODE 5) is selected via the AMx control
lines, the appropriate QM4 or QM5 output will be enabled.
These outputs can thus be used to control relays connected in
series with the high current amplifier as shown in Figure 8.
QM4
High
Low
CPOH
Low
High
CPOL
Low
High
Table VIII. CPCK Synchronous Logic Outputs
CLHDETECT
Low
High
CLLDETECT
Low
High
Table X. High Current Range Logic Outputs
QM5
Low
High
Table IX. Clamp Detect Outputs
Function
MEASVOUT or MEASIOUT < CPH
MEASVOUT or MEASIOUT > CPH
Function
MEASVOUT or MEASIOUT > CPL
MEASVOUT or MEASIOUT < CPL
Function
Current Range MODE 4 Enable Output
Current Range MODE 5 Enable Output
Function
Upper Clamp Inactive
Upper Clamp Active
Function
Lower Clamp Inactive
Lower Clamp Active
REV. A