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AD5520

Rev. B | Page 15 of 24

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. Settling times increase with

larger capacitances. ACx inputs select which external

compensation capacitor is used.

Table 10. AC0, AC1 Compensation Capacitor Selection

AC0

AC1

Function

Low

Select External Compensation Capacitor 0

High

Low

Select External Compensation Capacitor 1

Low

High

Select External Compensation Capacitor 2

COMPARATOR FUNCTION AND STROBING

The AD5520 has an on-board window comparator that

provides two bits of useful information, DUT too low or

DUT 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.

Table 11. Comparator Function Select

CPSEL

Function

Low

Compare CPL, CPH to MEASVOUT

High

Compare CPL, CPH to MEASIOUT

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. This indicates

whether the voltages at MEASIOUT or MEASVOUT have

exceeded voltages 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.

Table 12. CPCK Synchronous Logic Outputs

CPOH

Function

Low

High

MEASVOUT or MEASIOUT < CPH MEASVOUT or

MEASIOUT > CPH

CPOL

Function

Low

High

MEASVOUT or MEASIOUT > CPL MEASVOUT or

MEASIOUT < CPL

CLAMP FUNCTION

Clamp circuitry, which is also included on-chip, clamps the

force amplifier’s output if the voltage or current applied to the

DUT exceeds the clamp levels, CLL and CLH. The clamp

circuitry also comes into play in the event of a short or open

circuit. When in force current range, the voltage clamps protect

the DUT from an open circuit. Likewise, when forcing a voltage

and a short circuit occurs, the current clamps protect the DUT.

The clamps also function to protect the DUT if a transient

voltage or current spike occurs 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.

Table 13. Clamp Detect Outputs

CLHDETECT

Function

Low

Upper Clamp Inactive

High

Upper Clamp Active

CLLDETECT

Function

Low

Lower Clamp Inactive

High

Lower Clamp Active

HIGH CURRENT RANGES

With the use of an external high current amplifier, two high

current ranges are possible. The current range values can be set

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 appro-

priate QM4 or QM5 output is enabled. As a result, these outputs

can be used to control relays connected in series with the high

current amplifier, as shown in Figure 26.

Table 14. High Current Range Logic Outputs

QM4

QM5

Function

High

Low

Current Range Mode 4 Enable Output

Low

High

Current Range Mode 5 Enable Output

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