HC55151 datasheet(18/35 Pages) INTERSIL

18 / 35 page

4-18

EXAMPLE:

Calculate ZT to make ZTR = 600Ω in series with 2.16µF.

RP = 30Ω.

ZT = 114kΩ in series with 0.0108µF.

Note: Some impedance models, with a series capacitor, will

cause the op-amp feedback to behave as an open circuit

DC. A resistor with a value of about 10 times the reactance

of the ZT capacitor (2.16µF/200 = 10.8nF) at the low

frequency of interest (200Hz for example) can be placed in

parallel with the capacitor in order to solve the problem

(736k

Ω for a 10.8nF capacitor).

Calculating Tip and Ring Voltages

The on hook tip to ground voltage is calculated using

Equation 34. The minus 1.0 volt results from the SLIC self

programming. ISH- is the maximum loop current for a

constant on hook overhead voltage (ISH- = ISHD(0.6)) and

the value of RSAT(off) is calculated in Equation 4.

On hook Tip Voltage

The off hook tip to ground voltage is calculated using

Equation 35. ILOOP(min) is the minimum loop current

allowed by the design and the value of RSAT(off) is calculated

in Equation 4.

Off hook Tip Voltage

The on hook ring to ground voltage is calculated using

Equation 36. The 1.5 volt results from the SLIC self

programming. ISH- is the maximum loop current for a

constant on hook overhead voltage (ISH- = ISHD(0.6)) and

the value of RSAT(off) is calculated in Equation 4.

On hook Ring Voltage

The calculation of the ring voltage with respect to ground in

the off hook condition is dependent upon whether the SLIC

is in current limit or not.

The off hook ring to ground voltage (in current limit) is

calculated using Equation 37. ILIM is the programmed loop

current limit and RL is the load resistance across tip and

ring. The minus 0.2V is a correction factor for the 60k

Ω slope

in Figure 15.

Off hook Ring Voltage in Current Limit

The off hook ring to ground voltage (not in current limit) is

calculated using Equation 38. The 1.5V results from the

SLIC self programming. ILOOP(min) is the minimum loop

current allowed by the design and the value of RSAT(off) is

calculated in Equation 4.

Off hook Ring Voltage not in Current Limit

Layout Considerations

Systems with Dual Supplies (VBH and VBL)

If the VBL supply is not derived from the VBH supply, it is

recommended that an additional diode be placed in series

with the VBH supply. The orientation of this diode is anode

on pin 8 of the device and cathode to the external supply.

This external diode will inhibit large currents and potential

damage to the SLIC, in the event the VBH supply is shorted

to GND. If VBL is derived from VBH then this diode is not

required.

Floating the PTG Pin

The PTG pin is a high impedance pin (500k

Ω) that is used to

program the 2-wire to 4-wire gain to either 0dB or -6dB.

If 0dB is required, it is necessary to ﬂoat the PTG pin. The

PC board interconnect should be as short as possible to

minimize stray capacitance on this pin. Stray capacitance on

this pin forms a low pass ﬁlter and will cause the 2-wire to

4-wire gain to roll off at the higher frequencies.

If a 2-wire to 4-wire gain of -6dB is required, the PTG pin

should be grounded as close to the device as possible.

SPM Pin

For optimum performance, the PC board interconnect the

SPM pin should be as short as possible. If pulses metering

is not being used, then this pin should be grounded as close

to the device pin as possible.

RLIM Pin

The current limiting resistor RLIM needs to be as close to the

RLIM pin as possible.

Layout of the 2-Wire Impedance Matching

Resistor ZT

Proper connection to the ZT pin is to have the external ZT

network as close to the device pin as possible.

The ZT pin is a high impedance pin that is used to set the

proper feedback for matching the impedance of the 2-wire

side. This will eliminate circuit board capacitance on this pin

to maintain the 2-wire return loss across frequency.

200 600

ω2.16X10

–

-----------------------------------

() 30

()

–





(EQ. 33)

TIP onhook

()

1.0V

–

ISH-

()

–

SAToff

----------------------





(EQ. 34)

TIP offhook

()

–

LOOP min

()

SAT off

()

--------------------------

–

(EQ. 35)

LOOP MAX

() RP

–

RING onhook

()

1.5V

ISH

()

SAT off

()

--------------------------





(EQ. 36)

RING CL

()

TIP offhook

() ILOOP MAX

()RL

–

0.2V

–

(EQ. 37)

RING NCL

()

1.5V

LOOP min

()

SAT off

()

--------------------------





(EQ. 38)

LOOP MIN

() RP

–

HC55120, HC55121, HC55130, HC55131, HC55140, HC55141, HC55142, HC55143, HC55150, HC55151

HC55151 Datasheet(PDF) 18 Page - Intersil Corporation

HC55151 Datasheet(HTML) 18 Page - Intersil Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Datasheet Download

Link URL