SI3220-KQ Silicon Laboratories Inc, SI3220-KQ Datasheet - Page 37

• Manufacturer Part Number: SI3220-KQ
• Description: IC SLIC/CODEC DUAL-CH 64TQFP
• Manufacturer: Silicon Laboratories Inc
• Series: ProSLIC®r

Specifications of SI3220-KQ

• Package / Case: *
• Function: Subscriber Line Interface Concept (SLIC), CODEC
• Interface: GCI, PCM, SPI
• Number Of Circuits: 2
• Voltage - Supply: 3.3V, 5V
• Current - Supply: 65mA
• Power (watts): 941mW
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Includes: Battery Switching, BORSCHT Functions, DTMF Generation and Decoding, FSK Tone Generation, Modem and Fax Tone Detection
• Product: Telecom
• Supply Voltage (min): 3.13 V
• Supply Current: 22 mA
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Number Of Channels: 2
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Ground Key Detection
Ground Key detection detects an alerting signal from
the terminal equipment during the Active linefeed state
(forward or reverse polarity). The functional blocks
required to implement a Ground Key detector are
shown in Figure 21, and the register set for detecting a
ground key event is provided in Table 22. The primary
input to the system is the Longitudinal Current Sense
value provided by the voltage/current/power monitoring
circuitry and reported in the ILONG RAM address. The
ILONG value is processed in the ISP provided the LFS
bits in the Linefeed register indicate the device is in an
Active state. The output of the ISP is the input to a
programmable digital low-pass filter, which removes
unwanted ac signal components before threshold
detection.
The low-pass filter coefficient is calculated using the
equation below and is entered into the LONGLPF RAM
location.
Loop Closure Threshold (on-
hook to off-hook)
Loop Closure Threshold (off-
hook to on-hook)
Loop Closure Filter Coefficient
Loop Closure Mask Interval
Notes:
ILONG
1. I
2. The usable range for LCRONHK and LCROFFHK is limited to 61 mA. Entering a value > 61 mA will disable threshold
Table 21. Register and RAM Locations Used for Loop Closure Detection (Continued)
500 µA.
detection.
LOOP
is a calculated value based on measured I
Processor
Signal
Input
LFS
Figure 21. Ground Key Detection Circuitry
LCROFFHK
LCRONHK
LCRMASK
LCRLPF
LONGLPF
Digital
LPF
LONGHITH
Preliminary Rev. 0.91
Ground Key
Threshold
Q1
LCROFFHK[15:0] 0 to 101.09 mA
LCRONHK[15:0]
LCRMASK[15:0]
LCRLPF[15:3]
–I
LONGLOTH
Q4
–
+
increments. The resulting effective resolution is approximately
LONGLPF = [(2 π f x 4096)/800]
Where f = the desired cutoff frequency of the filter.
The programmable range of the filter is from 0 (blocks
all signals) to 4000h (unfiltered). A typical value of
10 Hz (0A10h) is sufficient to filter out any unwanted ac
artifacts while allowing the dc information to pass
through the filter.
The output of the low-pass filter is compared to the
programmable threshold, LONGHITH. Hysteresis is
enabled
LONGLOTH, to detect when the ground key is released.
The threshold comparator output feeds a programmable
debounce filter. The output of the debounce filter
remains in its present state unless the input remains in
the opposite state for the entire period of time
programmed by the loop closure debounce interval,
LONGDBI. If the debounce interval is satisfied, the
LONGHI bit is set to indicate that a valid loop closure
has occurred.
by
Debounce
LONGDBI
0 to 101.09 mA
Filter
0 to 40.96s
0 to 4000h
programming
Si3220/Si3225
2
2
LONGHI
Interrupt
LONGE
3.097 µ A
3.097 µ A
Logic
a
1.25 ms
N/A
second
396.4 µ A
396.4 µ A
1.25 ms
threshold,
N/A
LONGS
37