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AD5520

Rev. B | Page 16 of 24

CIRCUIT OPERATION

FORCE VOLTAGE

Most PMU measurements are performed while in force voltage

and measure current modes; for example, when the device is

used as a device power supply, or in continuity or leakage

testing. In the force voltage mode, the voltage at analog input

FIN is mapped directly to the voltage forced at the DUT.

When in force voltage and measure current modes, the

maximum voltage applied to the input corresponds to the

maximum current outputs. Figure 22 shows the transfer

function when forcing a voltage.

VDUT

VCLL ×

RS × 16

RDUT

VCLH ×

RS × 16

RDUT

RS × 16

VCLH

RS × 16

VCLL

VCLH

IDUT

VFIN

Figure 22. Force Voltage Transfer Function

MEASURE CURRENT

Figure 23 shows a simplified diagram of the PMU when in force

voltage mode. The control loop consists of the force amplifier

with the voltage sense amplifier making up the feedback path.

Current flowing through the DUT is measured by sensing the

current flowing through a selectable sense resistor, which is in

series with the DUT. The current sense amplifier (Gain = 16)

generates a voltage at its output, which is proportional to the

current flowing through the DUT. This voltage is compared to

the CLL and CLH levels to ensure the clamp voltages have not

been exceeded. Strobing CPCK and STB provides information

about the voltage level with respect to the comparator levels,

CPH and CPL.

MEASIHx

MEASIL

G= 16

MEASVH

MEASVL

G = 1

FOHx

RDUT

FIN

VMEASIOUT

VMEASVOUT

CLH

CLL

VCLL

VCLH

VFIN

CONDITION

OUTPUT

VCLH > IDUT × RS × 16

VCLL < IDUT × RS × 16

VDUT = VFIN

VDUT = VCLH

VDUT = VCLL

VCLH > IDUT × RS × 16

VCLL > IDUT × RS × 16

VCLH < IDUT × RS × 16

VCLL < IDUT × RS × 16

REFGNDI/V

Figure 23. Force Voltage, Measure Current Mode

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