ad5932 Analog Devices, Inc., ad5932 Datasheet - Page 18

• Manufacturer Part Number: ad5932
• Description: Programmable Frequency Scan Waveform Generator
• Manufacturer: Analog Devices, Inc.

AD5932
Therefore, in this example, a time interval of 20 ns × 2047 = 40 μs
is the maximum, with the minimum being 40 ns. For some
applications, this maximum time of 40 μs may be insufficient.
Therefore, to allow for sweeps that need a longer increment
interval, time-base multipliers are provided. D12 and D11 are
dedicated to the time-base multipliers, as shown in the bit map
above. A more detailed table of the multiplier options is given in
Table 9.
Table 9. Time-Base Multiplier Values
D12
0
0
1
1
If MCLK = 50 MHz and a multiplier of 500 is used, then the
base interval (T
a multiplier of 500, the maximum increment interval is 10 μs ×
2
gives the user enhanced flexibility when programming the
length of the frequency window, because any frequency can be
output for a minimum of 40 ns up to a maximum of 20.5 ms.
The above example shows a fixed number of clock periods.
Note that the same equally applies to fixed numbers of clock
cycles.
Length of Scan Time
The length of time to complete a user-programmed frequency
scan is given by the following equation:
ACTIVATING AND CONTROLLING THE SCAN
After the registers have been programmed, a 0 to 1 transition
on the CTRL pin starts the scan. The scan always starts from
the frequency programmed into the F
the value in the Δf register and increases by the number of steps
in the N
can be internally controlled using the t
controlled using the CTRL pin. The available options are
11 − 1
T
•
•
= 20.5 ms. Therefore, the option of time-base multipliers
SCAN
INCR
Auto-increment
External increment
= (1 + N
D11
0
1
0
1
register. However, the time interval of each frequency
BASE
INCR
) is now (1/(50 MHz) x 500)) = 10 μs. Using
) × T
Multiplier Value
Multiply (1/MCLK) by 1
Multiply (1/MCLK) by 5
Multiply (1/MCLK) by 100
Multiply (1/MCLK) by 500
BASE
START
INT
register or externally
register. It changes by
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Auto-Increment Control
The value in the t
AD5932 outputs each frequency for the length of time pro-
grammed in the T
frequency.
To set up the AD5932 to this mode, INT/EXT INCR (Bit D5)
must be set to 0.
External Increment Control
In this case, the time interval, t
CTRL pin. The first 0 to 1 transition on the pin starts the scan.
Each subsequent 0 to 1 transition on the CTRL pin increments
the output frequency by the value programmed into the Δf register.
To set up the AD5932 to this mode, INT/EXT INCR (Bit D5)
must be set to 1.
INTERRUPT Pin
This function is used as an interrupt during a frequency scan.
A low-to-high transition on this pin is sampled by the internal
MCLK, thereby resetting internal state machines, which results
in the output going to midscale.
STANDBY Pin
Sections of the AD5932 that are not in use can be powered
down to minimize power consumption. This is done by using
the STANDBY pin. For optimum power savings, it is recom-
mended to reset the AD5932 before entering standby. Doing so
reduces the power-down current to 20 μA.
When this pin is high, the internal MCLK is disabled, and the
reference, DAC, and regulator are powered down. When in this
state, the DAC output of the AD5932 remains at its present
value, because the NCO is no longer accumulating. When the
device is taken back out of standby mode, the MCLK is re-
activated, and the scan continues. To ensure correct operation
for new data, it is recommended that the device be internally
reset, using a control register write or using the INTERRUPT
pin, and then restarted.
INT
INT
register is used to control the scan. The
register, before moving on to the next
INT
, is set by the pulse rate on the