afs600 Actel Corporation, afs600 Datasheet - Page 96

• Manufacturer Part Number: afs600
• Description: Actel Fusion Programmable System Chips Mixed-signal Family With Optional Arm Support
• Manufacturer: Actel Corporation

To initiate a current measurement, the appropriate
Current Monitor Strobe (CMSTB) signal on the AB macro
must be asserted low for at least t
discharge the previous measurement. Then CMSTB must
be asserted high for at least t
Figure 2-71 • Timing Diagram for Current Monitor Strobe
Figure 2-72
operation. The differential voltage between AV and AC
goes into the 10× amplifier and is then converted by the
ADC. For example, a current of 1.5 A is drawn from a 10
V supply and is measured by the voltage drop across a
0.050 Ω sense resistor, The voltage drop is amplified by
ten times by the amplifier and then measured by the
ADC. The 1.5 A current creates a differential voltage
across the sense resistor of 75 mV. This becomes 750 mV
after amplification. Thus, the ADC measures a current of
1.5 A as 750 mV. Using an ADC with 8-bit resolution and
Figure 2-72 • Positive Current Monitor
2 -8 2
Actel Fusion Programmable System Chips
illustrates
ADCSTART
CMSTBx
V
0-12 V
ADC
positive
AVx
CMSET
Current Monitor
R
t
prior to asserting the
CMSLO
SENSE
CMSLO
current
CMSTBx
ACx
in order to
monitor
I
A d v a n c e d v 1 . 4
t
CMSET
10 X
ADCSTART can be asserted
after this point to start ADC
sampling.
ADCSTART signal. The CMSTB must remain high until
after the SAMPLE signal is de-asserted by the AB macro.
Note that the minimum sample time cannot be less than
t
in relationship with the ADC control signals.
VAREF of 2.56 V, the ADC result is decimal 75.
shows how to compute the current from the ADC result.
where
CMSHI
.
I is the current flowing through the sense resistor
ADC is the result from the ADC
VAREF is the Reference voltage
N is the number of bits
Rsense is the resistance of the sense resistor
t
Figure 2-71
CMSHI
I
V
=
ADC
(
ADC V
for MUX channel
(refer Table 2-36
shows the timing diagram of CMSTB
to Analog MUX
×
number)
AREF
)
⁄
(
10 2
×
N
×
R
sense
)
EQ 2-2
EQ 2-2