XE3005 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'XE3005' PDF : 37 Pages View PDF
XE3005/XE3006
• On-time (7:0): Time until wakeup. The number of sequential samples that have to be higher than the Reference for
the power down signal to become inactive. The Sandman™ function is disabled (SMAD or SMDA at logic 1) if this
parameter is zero. The ADC and DAC have one common On-time value.
All these parameters are set in the registers L, M, N, O and P.
Reference(7:0)
0
don’t care
don’t care
1.-.255
corresponds to
128.-.32640
On-time(7:0)
don’t care
0
don’t care
1.-.255
corresponds to
50 µs – 12 ms
Off-time(15:0)
don’t care
don’t care
0
1 - 65535
corresponds to
50 µs - 3.2 sec
Sandman (SMAD or SMDA)
logic 1 (disable function)
logic 1 (disable function)
logic 1 (disable function)
logic 1 (signal higher than ref)
logic 0 (signal lower than ref)
Comments
Sandman disable
Sandman disable
Sandman disable
all registers ≠ zero
time for FSYNC =
20kHz
The reference (7:0) value is related to the absolute value of the 16 bits input signal. The following format is used for the
comparison:
• 16 bit inputs data (2’s-complement) : 0111’1111’1111’1111 = 0x7FFF
• 8 bit reference (unsigned)
: 0111’1111’1000’0000 = 0xFF00/2
max positive value
reference max
So the reference is compared to the 8 most significant bits of the absolute value of the input signal:
reference(7:0)
0
1
2
M
255
Absolute reference
0
128
256
M
255 × 128 = 32640
AIN (mV) if gain = 4
0.00
1.10
2.20
M
280
AIN (mV) if gain = 20
0.00
0.27
0.55
M
70
The values in this table are amplitude values, RMS values can be derived by dividing the numbers by √2.
The working mechanism of the Sandman™ function is the following:
The incoming data is compared to the reference after each time step (1/FSYNC = 50µs if FSYNC = 20kHz).
• During the On-time phase
If the input data is higher than the reference, a counter will be incremented otherwise the counter is reset.
When the counter reaches the On-time value, then the SMAD or SMDA signal is activated (high level).
• During the Off-time phase
If the input data is lower than the reference, a counter will be incremented otherwise the counter is reset.
When the counter reaches the Off-time value, then the SMAD or SMDA signal is deactivated (low level).
In a first approximation, the following points are recommended:
• On-time at least 1ms. If the On-time is shorter than 1 ms, the Sandman™ function becomes sensitive to spikes in
the audio input signal AIN.
• Off-time at least 10ms, the Off-time should be longer than 1/fmin = 10ms, (code = 200). fmin is the minimum audio
frequency = 100Hz if FSYNC = 20kHz. The value of fmin scales proportionally with the sampling frequency FSYNC. A
high-pass filter in the ADC filters out signals below 100Hz.
• Reference should be adjusted just above the noise level.
© Semtech 2005
www.semtech.com
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