Datasheet

AD5522 Data Sheet
Rev. E | Page 32 of 64
MEASURE CURRENT GAINS
The measure current amplifier has two gain settings, 5 and 10.
The two gain settings allow users to achieve the quoted/specified
current ranges with large or small voltage swing. Use the 10 gain
setting with a 5 V reference, and use the 5 gain setting with a
2.5 V reference. Both combinations ensure the specified current
ranges. Using other VREF/gain setting combinations should
achieve smaller current ranges only. Achieving greater current
ranges than the specified ranges is outside the intended opera-
tion of the AD5522. The maximum guaranteed voltage across
R
SENSE
= ±1.125 V.
Following are examples of VREF/gain setting combinations. In
these examples, the offset DAC is at its default value of 0xA492.
• VREF = 5 V results in a ±11.25 V range. Using a gain setting
of 10, there is ±1.125 V maximum across R
SENSE
, resulting in
current ranges of ±5.625 μA, ±22.5 μA, and so on (inclu-
ding overrange of ±12.5% to allow for error correction).
• VREF = 2.5 V results in a ±5.625 V range. Using a gain setting
of 5 results in current ranges of ±5.625 μA, ±22.5 μA, and
so on (including overrange of ±12.5% to allow for error
correction).
VREF = 3.5 V results in a ±7.87 V range. Using a gain setting of
10, there is ±0.785 V maximum across R
SENSE
, resulting in
current ranges of ±3.92 μA, ±15.74 μA, and so on (including
overrange of ±12.5% to allow for error correction).
VMID VOLTAGE
The midcode voltage (VMID) is used in the measure current
amplifier block to center the current ranges about 0 A. This
is required to ensure that the quoted current ranges can be
achieved when using offset DAC settings other than the default.
VMID corresponds to 0x8000 or the DAC midcode value, that
is, the middle of the voltage range set by the offset DAC setting
(see Table 13). See the block diagram in Figure 48.
VMID = 4.5 × VREF × (32,768/2
16
) − (3.5 × VREF ×
(OFFSET_DAC_CODE/2
16
))
or
VMID = 3.5 × VREF × ((42,130 − OFFSET_DAC_CODE)/2
16
)
VMIN = −3.5 × VREF × (OFFSET_DAC_CODE/2
16
)
VREF
VTOP
VMID
VDAC_MID
VOFFSET
DAC HV AMP
SEL×10
SEL×10
MEASVHx
DUTGND
INT/EXTMEASIHx
MEASURE
CURRENT
IN-AMP
MEASURE
VOLTAGE
IN-AMP
INT/EXTMEASILx
06197-043
SEL×5
1R
1R
1R
1R
1R
1R
10R
10R
1R
1R
ATT
R
AGND
SEL×5
5R
5R
5R
2R 7R
2R 7R
VOFFSET
DAC HV AMP
AGND
ATTB
ATTB
REFGND
MEASOUTx
ATT = ATTENUATION FOR MEASOUTx ×0.2
MI = MEASURE CURRENT
MV = MEASURE VOLTAGE
SEL×5 = MI GAIN = 5
SEL×10 = MI GAIN = 10
ATTB
ATT
MI
MV
INAMP10
INAMP1
VMIN
VDAC_MIN
DATA
ADDRESS
DAC
50Ω
Figure 48. Measure Block and VMID Influence