AD5522JSVDZ datasheet(33/60 Pages) AD

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AD5522

Rev. A | Page 33 of 60

When configured as DUTGND per channel, this dual function

pin is no longer connected to the input of the guard amplifier.

Instead, it is connected to the low end of the instrumentation

amplifier (SW14a), and the input of the guard amplifier is

connected internally to MEASVHx (SW13a).

DUTGND

MEASURE

VOLTAGE

IN-AMP

MEASVH[0:3]

GUARD[0:3]

GUARDIN[0:3]/

DUTGND[0:3]

DUT

GUARD

AMP

SW14

SW13

SW16

–

AGND

Figure 46. Using the DUTGND per Channel Feature

GUARD AMPLIFIER

A guard amplifier allows the user to bootstrap the shield of the

cable to the voltage applied to the DUT, ensuring minimal drops

across the cable. This is particularly important for measurements

requiring a high degree of accuracy and in leakage current testing.

If not required, all four guard amplifiers can be disabled via the

serial interface (system control register). Disabling the guard

amplifiers decreases power consumption by 400 μA per channel.

As described in the Device Under Test Ground (DUTGND)

section, GUARDINx/DUTGNDx are dual function pins. Each

pin can function either as a guard amplifier input for one

channel or as a DUTGND input for one channel, depending

on the requirements of the end application (see Figure 46).

A guard alarm event occurs when the guard output moves more

than 100 mV away from the guard input voltage for more than

200 μs. In this case, the event is flagged via the open-drain

output CGALM. Because the guard and clamp alarm functions

share the same alarm output, CGALM, the alarm information

(alarm trigger and alarm channel) is available via the serial

interface in the alarm status register.

Alternatively, the serial interface allows the user to set up the

CGALM output to flag either the clamp status or the guard

status. By default, this open-drain alarm pin is an unlatched

output, but it can be configured as a latched output via the serial

interface (system control register).

COMPENSATION CAPACITORS

Each channel requires an external compensation capacitor

(CCOMP) to ensure stability into the maximum load capacitance

while ensuring that settling time is optimized. In addition, one

CFF pin per channel is provided to further optimize stability

and settling time performance when in force voltage (FV) mode.

When changing from force current (FI) mode to FV mode, the

switch connecting the CFF capacitor is automatically closed.

Although the force amplifier is designed to drive load capacitances

up to 10 nF (with CCOMP = 100 pF), it is possible to use larger

compensation capacitor values to drive larger loads, at the

expense of an increase in settling time. If a wide range of load

capacitances must be driven, an external multiplexer connected

to the CCOMP pin allows optimization of settling time vs.

stability. The series resistance of a switch placed on CCOMP

should typically be <50 Ω.

Suitable multiplexers for use here are the ADG1404, ADG1408,

or one of the multiplexers in the ADG4xx family which

typically have on resistances less than 50 Ω.

Similarly, connecting the CFF node to an external multiplexer

accommodates a wide range of CDUT in FV mode. The

ADG1204 or ADG1209 family of multiplexers meet these

requirements. The series resistance of the multiplexer used

should be such that

1/(2π × RON × CDUT) > 100 kHz

Table 12. Suggested Compensation Capacitor Selection

CLOAD

CCOMP

CFF

≤1 nF

100 pF

220 pF

≤10 nF

100 pF

1 nF

≤100 nF

CLOAD/100

CLOAD/10

SYSTEM FORCE AND SENSE SWITCHES

Each channel has switches to allow connection of the force

(FOHx) and sense (MEASVHx) lines to a central PMU for

calibration purposes. There is one set of SYS_FORCE and

SYS_SENSE pins per device. It is recommended that these

connections be made individually to each PMU channel.

FOH0

FOH1

FOH2

FOH3

SYS_FORCE

MEASVH0

MEASVH1

MEASVH2

MEASVH3

SYS_SENSE

Figure 47. SYS_FORCE and SYS_SENSE Connections to FOHx and MEASVHx Pins

TEMPERATURE SENSOR

An on-board temperature sensor monitors die temperature. The

temperature sensor is located at the center of the die. If the

temperature exceeds the factory specified value (130°C) or a

user programmable value, the device protects itself by shutting

down all channels and flagging an alarm through the latched,

open-drain TMPALM pin. Alarm status can be read back from

the alarm status register or the PMU register, where latched and

unlatched bits indicate whether an alarm has occurred and

whether the temperature has dropped below the set alarm

temperature. The shutdown temperature is set using the system

control register.

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