Si3220/Si3225
Setting the linefeed register to the opposite polarity A wink function slowly ramps down the TIP-RING
immediately reverses (hard reversal) the line polarity. voltage (V ) to 1 followed by a return to the original
OC
For example, to transition from Forward Active mode to VOC value (set in the VOC RAM location). This scheme
Reverse Active mode changes LF[2:0] from 001 to 101. lights a message-waiting lamp in certain handsets. No
Polarity reversal is accommodated in the OHT and change to the linefeed register is necessary to enable
ground start modes. The POLREV bit is a read-only bit this function. Instead, the user sets the VOCZERO bit to
that reflects if the device is in polarity reversal mode. 1 so that the TIP-RING voltage collapses to 0 V at the
For smooth polarity reversal, set the PREN bit to 1 and rate programmed by the RAMP bit. Setting the
the RAMP bit to 0 or 1 depending on the desired ramp VOCZERO bit back to 0 returns the TIP-RING voltage
rate (see Table 32). Polarity reversal is then to its normal setting. With a software timer, the user can
accomplished by toggling the linefeed register from automate the cadence of the wink function. Figure 32
forward to reverse modes as desired.
illustrates the wink function.
Table 32. Register and RAM Locations used for Polarity Reversal
Parameter
Programmable Range
Register/RAM Register/RAM
Bits
Mnemonic
LINEFEED
POLREV
Linefeed
See Table 17
Read only
LF[2:0]
Polarity Reversal Status
POLREV
VOCZERO
Wink Function
(Smooth transition to Voc=0V)
1 = Ramp to 0 V
0 = Return to previous V
OC
POLREV
Smooth Polarity Reversal Enable 0 = Disabled
1 = Enabled
PREN
RAMP
POLREV
POLREV
Smooth Polarity Reversal Ramp
Rate
0 = 1 V/1.25 ms
1 = 2 V/1.25 ms
Set VOCZERO bit to 1
Set VOCZERO bit to 0
40 50
0
10
20
30
60
70
Vcm
80
VTIP
Time (ms)
0
-10
-20
-30
-40
-50
2V/1.25ms slope
set by RAMP bit
Voc
VRING
VBAT
Vov
VTIP/RING (V)
Figure 32. Wink Function with Programmable Ramp Rate
Rev. 1.0
57
SILICONIMAGE [ Silicon image ]
