LH2559
High-Voltage Interface IC
Polarity Guard and Switch Hook Control
FEATURES
¥
Low voltage drop polarity guard (1.4 V
max at 20 mA), ideal for line-powered
DAA circuits
¥
On-chip protection for associated
DAA circuitry
¥
Isolated switchhook, suitable for pulse
dialing
¥
Three functions integrated into one
package, ideal for space-constrained
applications
¥
Isolation in excess of 3750 Vrms to
facilitate meeting domestic and foreign
regulatory requirements
¥
Easy interface to AT&T and other
DAA circuits
¥
Ideal for use in modems, answering
machines, FAX machines, and other
customer premises equipment
APPLICATIONS
¥
Modems
¥
FAX machines
¥
Answering machines
¥
Key telephone systems
¥
Equipment attached to the customer
premises side of the telephone line
DESCRIPTION
The LH2559 High-Voltage Interface IC is an integrated high-
voltage switch that contains a solid-state switchhook relay, a
low-voltage drop polarity guard, and a protection circuit across
the outputs.
The solid-state switchhook relay is an optically coupled, low ON-
resistance, MOSFET device. The 8-pin DIP/SOG version has an
insulating barrier of 3750 Vrms. This device has a voltage break-
down rating of 400 V.
A feature of this device is the polarity guard. A combination of
diodes and MOSFETs provides for a low-voltage drop on long
loops. The maximum voltage drop across both the polarity guard
and the solid-state switchhook relay is only 1.4 V at 20 mA.
The 18 V protection circuit is provided to ensure the integrity of
coupled low-voltage DAA circuitry, such as AT&T’s ATTD2560
Interface Circuit for Optically Coupled Data Access Arrangements.
The LH2559 is packaged in an 8-pin DIP (LH2559AB) or in an 8-
pin surface-mount gull-wing package (LH2559AAC).
Figure 1. Functional Block Diagram
TIP
POLARITY
GUARD
SWITCHHOOK
CONTROL
TIPP
RING
PROT.
RINGP
Pin Information
Figure 2. 8-Pin DIP Diagram for LH2559
LEDA
LEDA
LEDC
NC
1
2
3
4
8
7
6
5
TIPP
RINGP
TIP
RING
1
Table 1. PIN Descriptions for 8-Pin DIP/SOG Package
DIP/SOG
1
2
3
4
5
6
7
8
Symbol
LEDA
LEDA
LEDC
NC
RING
TIP
RINGP
TIPP
Description
The anode side of the LED that controls the switch.
The anode side of the LED that controls the switch.
The cathode side of the LED that controls the switch.
No connection. Do NOT use as tie points.
Ring conductor of the incoming telephone line.
Tip conductor of the incoming telephone line.
Ring conductor of the telephone line on the user side of the polarity guard.
This is a polarized RING conductor, negative with respect to TIPP.
Tip conductor of the telephone line on the user side of the switchhook.
This is a switched and polarized positive TIP conductor.
The polarity guard functions as a diode bridge, always
biasing the TIPP lead positive with respect to the RINGP
lead. A combination of MOSFETs and diodes is used to
reduce the forward voltage drop through the device
(including the switchhook) to 1.4 V maximum at 20 mA.
This allows a full 4.6 V to be available to the other DAA
circuitry on the equipment side of the switchhook and
while still meeting the requirements of FCC Part 68 on a
long loop. The device also contains an internal 18 V
protection circuit to protect external equipment
connected to the outputs of the device during the off-
hook state.
Functional Description
As shown in Figure 1, the LH2559 contains three func-
tional blocks: a solid-state switchhook relay, a polarity
guard, and a protection circuit.
The switchhook function is performed by using an
isolated MOSFET switch that has an ON-resistance of
approximately 7
Ω.
This switch is controlled by an opti-
cally coupled, isolated relay-driver circuit. The relay-
driver circuit is controlled by the LED input pins. When
current is applied to the LED, the switch goes to an off-
hook condition. The LED has an input/output isolation of
3750 Vrms, and the MOSFET switch has a breakdown
voltage of 400 V. These parameters will easily meet the
isolation/breakdown requirements of many regulatory
agencies.
Absolute Maximum Ratings (At 25°C)
Stresses in excess of the Absolute Maximum Ratings
can cause permanent damage to the device. These are
absolute stress ratings only. Functional operation of the
device is not implied at these or any other conditions in
excess of those indicated in the operational sections of
the data sheet. Exposure to Absolute Maximum Ratings
for extended periods can adversely affect device reli-
ability.
Parameter
Power Supply
Ambient Operating Temperature Range
Pin Soldering Temperature: (t=10 s max)
8-pin DIP/SOG
Input/Output Isolation Voltage: (t=60 s min)
8-pin DIP/SOG
Breakdown Voltage
TIP—TIPP
LED Input Ratings:
Continuous Forward Current
Reverse Voltage (I
R
≤10 µA)
Symbol
V
SS
T
A
T
S
V
ISO
V
BD
Value
5 V
±
10%
0 to 70
260
3750
400
Unit
V
°C
°C
Vrms
V
I
F
V
R
50
5
mA
V
LH2559 and LH2559ACE
2
Electrical Specifications (T
A
=25°C)
Minimum and maximum values are testing requirements.
Typical values are characteristics of the device and
are the result of engineering evaluations. Typical values
are for information purposes only and are not part of the
testing requirements.
Table 2. Device Characteristics
Parameter
Off-state
Leakage Current
Total ON-resistance
Symbol Test Condition
I
TIPP
R
ON
I
F
=0 mA, V
TIP
=400 V, V
RING
=0 V,
TIPP and RINGP tied together
I
F
=5 mA, I
TIP
=30 mA, V
RING
=0 V
R
ON
=[V (50 mA) – V (20 mA)]
÷
30 mA
TIPP and RINGP tied together
I
F
=5 mA, I
TIP
=20 mA, V
RING
=0 V,
TIPP and RINGP tied together
V
TIPP
=0 V, V
L
=50 V, TIP=R
L
, R
L
=1 kΩ ,
I
F
=step from 0 mA to 5 mA
V
TIPP
=0 V, V
L
=50 V, TIP=R
L
, R
L
=1 kΩ ,
I
F
=step from 5 mA to 0 mA*
I
F
=0 mA,
Voltage applied between TIP and RING,
TIPP and RINGP tied together
Between pins 1—4 and 5—8
I
TIP
=100 mA, t=5 ms
V
TIP
V
TIPP
=400 V, t=5 ms
I
F
=10 mA
—
—
Min
—
12
Typ
—
—
Max
16
24
Unit
µA
Ω
Total On-state Voltage
Turn-on Time
Turn-off Time
Breakdown Voltage
V
TIP
t
on
t
off
V
BD
—
—
—
400
—
—
—
—
1.4
5
5
—
V
ms
ms
V
Isolation Voltage:
8-pin DIP/SOG
LED Forward Current
for Switch Turn-on
LED Forward Current
for Switch Turn-off
LED Forward Voltage
LED Reverse
Breakdown Voltage
Protection Voltage
—
I
FON
I
FOFF
V
F
V
LBD
V
PROT
3750
—
0.01
1.15
5
16
—
0.2
0.1
1.26
—
18
—
5
—
1.45
—
20
Vrms
mA
mA
V
V
V
*V
L
is a power supply connected to the TIP pin through a resistance R
L
.
LH2559 and LH2559ACE
3
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