AD5520 datasheet(12/20 Pages) AD

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REV. A

–12–

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.

Table V. Selection of Current Range

AM0

AM1

AM2

Function

Low

Current Range MODE0 (up to 4

µA)

High

Low

Current Range MODE1 (up to 40

µA)

Low

High

Low

Current Range MODE2 (up to 400

µA)

High

Low

Current Range MODE3 (up to 4 mA)

Low

High

Current Range MODE4 (External

Buffer Mode)

High

Low

High

Current Range MODE5 (External

Buffer Mode)

Low

High

Standby (same as STANDBY = High)

High

Standby (same as STANDBY = High)

RS Selection

The AD5520 is designed so that the voltage drop across each of

the RS resistors will be less than

±500 mV when maximum current

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.

Table VI. 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 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.

Table VII. 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, 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.

Table VIII. CPCK Synchronous Logic Outputs

CPOH

Function

Low

MEASVOUT or MEASIOUT < CPH

High

MEASVOUT or MEASIOUT > CPH

CPOL

Function

Low

MEASVOUT or MEASIOUT > CPL

High

MEASVOUT or MEASIOUT < CPL

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.

Table IX. 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

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.

Table X. 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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