AD5522JSVUZ datasheet(32/60 Pages) AD

32 / 60 page

AD5522

Rev. A | Page 32 of 60

CHOOSING POWER SUPPLY RAILS

As noted in the Specifications section, the minimum supply

variation across the part |AVDD − AVSS| ≥ 20 V. For the

AD5522 circuits to operate correctly, the supply rails must take

into account not only the force voltage range, but also the

internal DAC minimum voltage level, as well as headroom and

so on. The DAC amplifier gains VREF by 4.5, and the offset

DAC centers that range about some chosen point.

The supplies need to cater to the DAC output voltage range to

avoid impinging on other parts of the circuit (for example, if the

measure current block for rated current ranges has a gain of

10/5, the supplies need to provide sufficient headroom and

footroom to not clip the measure current circuit when full

current range is required).

Also, the measout gain = 0.2 setting uses the VMIN level for

scaling purposes; if there is not enough footroom for this

VMIN level, then the MV and MI output voltage range is

affected.

For the measout gain = 0.2 setting, it is important to choose

AVSS based on the following:

AVSS ≤ −3.5 × (VREF × (OFFSET_DAC_CODE/216)) −

AVSS_footroom − VDUTGND − (RCABLE × ILOAD)

where:

AVSS_footroom = 4 V.

VDUTGND is the voltage range anticipated at DUTGND.

RCABLE is the cable/path resistance.

ILOAD is the maximum load current.

MEASURE OUTPUT (MEASOUTx PINS)

The measured DUT voltage or current (voltage representation

of DUT current) is available on the MEASOUTx pin with respect

to AGND. The default MEASOUTx range is the forced voltage

range for voltage measure and current measure (nominally

±11.25 V, depending on the reference voltage and offset DAC)

and includes some overrange to allow for offset correction.

The serial interface allows the user to select another MEASOUTx

range of 0.9 × VREF to AGND, allowing an ADC with a 5 V

input range to be used. The MEASOUTx line for each PMU

channel can be made high impedance via the serial interface.

The offset DAC directly offsets the measured output voltage level,

but only when GAIN1 = 0. When the MEASOUTx gain is 0.2, the

minimum code from the DAC is used to center the MEASOUTx

voltage and to ensure that the voltage is within the range of 0 to

0.9 × VREF (see Figure 45).

When using low supply voltages, ensure that there is sufficient

headroom and footroom for the DAC output range (set by the

VREF and offset DAC setting).

DEVICE UNDER TEST GROUND (DUTGND)

By default, there is one DUTGND input available for all four

PMU channels. However, in some PMU applications, it is

necessary that each channel operate from its own DUTGND

level. The dual function pin, GUARDINx/DUTGNDx, can be

configured as an input to the guard amplifier (GUARDIN) or

as a DUTGND input for each channel.

The pin function can be configured through the serial interface

on power-on for the required operation. The default connection

is SW13b (GUARDIN) and SW14b (shared DUTGND).

Table 10. MEASOUTx Output Ranges for GAIN1 = 0, MEASOUT Gain = 1

MEASOUT

Function

Measure

Current Gain

Transfer Function

Output Voltage Range for VREF = 5 V1

Offset DAC = 0x0

Offset DAC = 0xA492

Offset DAC = 0xED67

5 or 10

±VDUT

0 V to 22.5 V

±11.25 V

−16.26 V to +6.25 V

GAIN0 = 0

(IDUT × RSENSE × 10) + VMID

0 V to 22.5 V

±11.25 V

−16.26 V to +6.25 V

GAIN0 = 1

(IDUT × RSENSE × 5) + VMID

0 V to 11.25 V

(VREF = 2.5 V)

±5.625 V

(VREF = 2.5 V)

−8.13 V to +3.12 V

(VREF = 2.5 V)

1 VREF = 5 V unless otherwise noted.

Table 11. MEASOUTx Output Ranges for GAIN1 = 1, MEASOUT Gain = 0.2

MEASOUT

Function

Measure

Current Gain

Transfer Function

Output Voltage Range for VREF = 5 V1, 2

5 or 10

VDUT × 0.2 + (0.45 × VREF)

0 V to 4.5 V (±2.25 V centered around 2.25 V)

GAIN0 = 0

(IDUT × RSENSE × 10 × 0.2) + (0.45 × VREF)

0 V to 4.5 V (±2.25 V centered around 2.25 V)

GAIN0 = 1

(IDUT × RSENSE × 5 × 0.2) + (0.45 × VREF)

1.125 V to 3.375 V (±1.125 V, centered around 2.25 V)

0 V to 2.25 V (±1.125 V, centered around 1.125 V)

(VREF = 2.5 V)

1 VREF = 5 V unless otherwise noted.

2 The offset DAC setting has no effect on the output voltage range.

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