HC5549 Datasheet, PDF (10/13 Pages) Intersil Corporation – Low Power SLIC with Battery Switch

HC5549
Power Dissipation
The power dissipation during ringing is dictated by the load
driving requirements and the ringing waveform. The key to
valid power calculations is the correct definition of average
and rms currents. The average current defines the high
battery supply current. The rms current defines the load
current.
The cadence provides a time averaging reduction in the
peak power. The total power dissipation consists of ringing
power, P_r, and the silent interval power, P_s.
P_RNG= P_r ⋅ _t--_r----+^t--^r---_t-_s- + P_s ⋅ -_t-_r----^t_+-^s----_t-_s-
(EQ. 32)
The terms, tr and ts, represent the cadence. The ringing
interval is tr and the silent interval is ts. The typical cadence
ratio tr:ts is 1:2.
The quiescent power of the device in the ringing mode is
defined in Equation 34.
P_r(Q)= VBH ⋅ IBH_Q + VBL ⋅ IBL_Q + VCC ⋅ ICC_Q
(EQ. 33)
During ringing, the device is operated from the low battery,
therefore the VBH power contribution is negligible. The total
power during the ringing interval is the sum of the quiescent
power and loading power:
P_r=
P_r(Q) + VBL
⋅
I_AVG –
---------------^V----^r2--^m-----^s---------------
Z_REN + R_LOOP
(EQ. 34)
For sinusoidal waveforms, the average current, I_AVG, is
defined in equation 36.
I_AVG=


2_{-π-}
--------^V-----^r--^m-----^s----^â‹--------²---------
Z_REN + R_LOOP
(EQ. 35)
The only amplifier providing load current during ringing is the
Tip amplifier. Therefore the total power contribution from the
device is half the average power required by the load.
I_AVG=


1_{-π-}
Z^----_R^----V-_E^----_Nr^{--m---+--s---}R^-⋅---_L^----_O^-2---_O^-----_P^-
(EQ. 36)
The silent interval power dissipation will be determined by
the quiescent power of the selected operating mode.
Power Denial
Overview
The power denial mode (111) will shutdown the entire device
except for the logic interface. Loop supervision is not
provided. This mode may be used as a sleep mode or to
shutdown in the presence of a persistent thermal alarm.
Switching between high and low battery will have no effect
during power denial.
Functionality
During power denial, both the Tip and Ring amplifiers are
disabled, representing high impedances. The voltages at
both outputs are near ground.
Thermal Shutdown
In the event the safe die temperature is exceeded, the ALM
output will go low and DET will go high and the part will
automatically shut down. When the device cools, ALM will go
high and DET will reflect the loop status. If the thermal fault
persists, ALM will go low again and the part will shutdown.
Programming power denial will permanently shutdown the
device and stop the self cooling cycling.
Battery Switching
Overview
The integrated battery switch selects between the high
battery (VBH) and low battery (VBL). The battery switch is
controlled with the logic input BSEL. When BSEL is a logic
high, the high battery is selected and when a logic low, the
low battery is selected. All operating modes of the device will
operate from high or low battery except forward loop back.
Functionality
The logic control is independent of the operating mode
decode. Independent logic control provides the most
flexibility and will support all application configurations.
When changing device operating states, battery switching
should occur simultaneously with or prior to changing the
operating mode. In most cases, this will minimize overall
power dissipation and prevent glitches on the DET output.
The only external component required to support the battery
switch is a diode in series with the VBH supply lead. In the
event that high battery is removed, the diode allows the
device to transition to low battery operation.
Low Battery Operation
All off hook operating conditions and ringing should use the
low battery. The prime benefit will be reduced power
dissipation. The typical low battery for the device is -24V.
However this may be increased to support longer loop
lengths or high loop current requirements. Standby
conditions may also operate from the low battery if MTU
compliance is not required, further reducing standby power
dissipation.
High Battery Operation
The high battery should be used for standby conditions
which must provide MTU compliance. During standby
operation the power consumption is typically 40 mW with -
48V battery. If standby requirements do not require high
battery operation, then a lower battery will result in lower
standby power.
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