HC55120_06 Datasheet, PDF (15/36 Pages) Intersil Corporation – Low Power Universal SLIC Family

HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150
VBH
2.5V †
SLIC SELF PROGRAMMING
VOH(on) AT LOAD
R_SAT
VOH(off) AT LOAD
CONSTANT
CURRENT
REGION
RLOOP(max)
IOH
ISH-
I_SHD
ILOOP(min)
LOOP CURRENT (mA)
†Internal overhead voltage automatically generated by the SLIC.
FIGURE 15. UniSLIC14 DC FEED CURVE
60kΩ SLOPE
ILOOP(max)
On Hook Overhead Voltage
DC FEED CURVE
V_BH
2.5V
The on hook overhead
voltage at the load (V_OH(on)
at Load) is independent of the
V_OH(on)
ON HOOK
OVERHEAD
V_BH battery voltage. Once
set, the on hook voltage
remains constant as the V_BH
battery voltage changes. The
ISH- I_SHD
LOOP CURRENT
ISH- = I_SHD(0.6)
on hook voltage also remains
constant over temperature
and line leakages up to 0.6
times the Switch Hook Detect threshold (I_SHD). The
maximum loop current for a constant on hook overhead
voltage is defined as ISH-.
The on hook overhead voltage, required for a given signal
level at the load, must take into account the AC voltage drop
across the 2 external protection resistors (R_P) and the 2
internal sense resistors (R_S) as shown in Figure 16. The AC
on hook overload voltage is calculated using Equation 1.
V_{OH(on) at Load}
=
V_s
p(
on
)
×
⎛
⎜
⎝
1
+
2_----R_{-----P---Z--+--L---}2_----R_{----S--⎠⎟⎞}
+ 1.5V
(EQ. 1
where
V_{OH(on) at Load} = On hook overhead voltage at load
V_sp(on) = Required on hook transmission for speech
R_P = Protection Resistors (Typically 30Ω)
R_S = Internal Sense Resistors (40Ω)
Z_L = AC load impedance for (600Ω)
1.5V = Additional on hook overhead voltage requirement
15
To account for any process and temperature variations in the
performance of the SLIC, 1.5V is added to the overhead
voltage requirement for the on hook case in Equation 1 and
2.0V for the off hook case in Equation 3. Note the 2.5V
overhead is automatically generated in the SLIC and is not
part of the external overhead programming.
EXTERNAL PROTECTION
RESISTOR
REQUIRED
OVERHEAD VOLTAGE
V_OH (ON, OFF)
UniSLIC14
2R_P
2R_S
V_ZL
TIP AND RING
AMPLIFIERS
Z_L
(LOAD)
INTERNAL SENSE
RESISTORS
V_{OH(ON, OFF)}
=
⎛
⎜
⎝
2_----R_{-----P---Z--+--L---}2_----R_{----S--⎠⎟⎞}
V_ZL
Where:
V_ZL is the required on hook or offhook
transmission delivered to the load.
FIGURE 16. OVERHEAD VOLTAGE OF THE TIP AND RING
AMPLIFIERS
FN4659.13
June 1, 2006