INTERSIL AN1082

Using the ISL6401 RSLIC PWM Controller
Evaluation Board
®
Application Note
October 2003
AN1082
Author: Manisha Pandya, Jason Houston
Functional Description
The ISL6401 pulse width modulating (PWM) current mode
controller is designed for a wide range of DC-DC conversion
applications including boost, flyback, and isolated output
configurations. The device is optimized to provide high
performance, low-cost solution for Ringing SLIC (RSLIC)
Ring (Vbh) and Talk (Vbl) power supplies in VoIP
applications. The IC features an integrated inverter that is
ideal for generating negative output voltage like RSLIC Ring
Vbh (-72V) and Talk Vbl (-24V), -48V for IP Phones, -5V and
-15V for DSL CO line drivers. The output voltages are
adjusted with an external voltage divider.
Peak current mode control architecture effectively handles
Ring trip transients and provides inherent over-current
protection. Flyback topology allows the operation close to
50% duty cycle, offering optimum transformer utilization, low
ripple current and less stress on input/output capacitors.
Internal soft start minimizes start-up stress without any
external components. The switching frequency can be
programmed from 50kHz to 600kHz or alternatively the
internal oscillator can be locked to an external clock fed at
SYNC input for noise sensitive applications. A logic level
shutdown input is included, which reduces supply current to
55µA in the shutdown mode. DC-DC conversion efficiency is
optimized by use of a low current sense voltage.
For a detailed functional description, complete specifications
and component selection guidelines, please refer to the
ISL6401 Data Sheet, Intersil Corporation, File No. FN9007,
available on Intersil’s website, http://www.intersil.com/
Application Information
As worldwide demand for inexpensive Voice over Internet
Protocol telephony grows, so will the need for Integrated
Circuits that are specialized to enable compatibility between
new telephony systems and older telephones based on
analog standards. Analog ring signal generation and off
hook loop current supply are two analog functions that are
performed by Subscriber Line Interface Circuits (SLICs).
This application note discusses the special power supply
implementation to generate the high negative voltages
needed by SLICs.
In a telephone loop, the subscriber is connected to the
network via 2 wires, commonly known as Tip and Ring. The
actual digital telecommunications trunk line however,
operates on 4-wires; two of which are allocated for
transmitting and two for receiving. This 2 to 4-wire interface
consists of the SLIC and CODEC. A SLIC is the primary
interface between the 4-wire (ground referenced) low
voltage switch environment and the 2 wire (floating) high
voltage loop environment. It performs a number of important
functions including Battery feed, Overvoltage protection,
Ringing, Signaling, Coding, Hybrid Balancing and also
Testing.
The Ringing SLIC (RSLIC) typically requires two high
voltage power supply inputs. The first is a tightly regulated
voltage around -24V or -48V for off-hook signal transmission.
The second is a loosely regulated -70 to -100V for ring tone
generation. When the switch hook is released the phone
puts approximately 200Ω of resistance across the phone
terminals. Intersil RSLICs feature internal current limiting so
this load is not presented to the power supply. However, not
all of the SLICs available in the market offer this feature and
the power supply is expected to maintain output during the
remainder of the ring cycle. Once voice transmission begins,
the SLIC, in many cases, requires a lower voltage input to
establish a 20-25mA current loop. The loop feeds the 200Ω,
protection resistors, and line resistances within the phone. In
some cases, the lower supply and higher supply voltage are
combined and the SLIC runs from a compromise voltage of
approximately -53V.
The specifications below are for a 4-line requirement with
5 REN per line
TABLE 1. TYPICAL POWER SUPPLY REQUIREMENT FOR
VoIP RESIDENTIAL GATEWAY
PARAMETER
Input Voltage
5 or 12 volts
Output Power
3 to 10 watts
Efficiency
80 to 90%
Output Voltages
-24V, -72 to -100V and/or
-48V
-24V Requirements (4 lines)
Regulation: ±5% Maximum
Output Current: 0.10A Ripple:
Less than 0.25Vpp
-72V Requirements (4 lines)
Regulation: ±10% Maximum
Output Current: 0.10A Ripple:
Less than 1Vpp
Overview of Telephone loop system
Traditionally a telephone network consists of a circuit
between the subscriber and the central office. However, the
advent of new high speed digital technologies have created
the need to control and manage the functions of the phone
locally as opposed to the central office. In both instances the
principals governing the operation of the phone loop are
essentially the same.
1
REQUIREMENT
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Application Note 1082
Using the ISL6401 Evaluation Board
The ISL6401EVAL1E Schematic shows a current mode
power supply using the Intersil ISL6401 in standard flyback
topology. The ISL6401EVAL1 evaluation board is shipped
“ready to use” right from the box. The IC requires +5V Bias.
The evaluation board input voltage can be 10V to 16V with
the specified transformer and external components. The
output voltages are -24V at 120mA and -72V at 120mA. The
board is capable of evaluating device operation with loads
that simulate one, two, three or four line operation. The use
of an electronic load enables evaluation over a wide range of
operating conditions. Simply vary the load on each output
from 0 - 120mA in any combination to match exact
application requirements. The circuit uses off the shelf
inexpensive transformers to generate both outputs using a
single controller. The transformer turns ration is 1:1:1:1
where 24V appear across each secondary winding and the
primary during the switch off time. The remaining secondary
windings are stacked in series to develop -48V. The -48V
section is then stacked on the -24V section to get the -72V.
This technique provides good cross regulation, lowers the
voltage rating required for the output capacitors and lowers
the RMS current, allowing the use of cheaper output
capacitors. Also, the selection of a transformer with multifilar
winding lowers the leakage inductance and cost. The cross
regulation of both output is achieved by using split feedback
for both outputs where the feedback factor can be weighed
based on load condition on both outputs.
TABLE 2. ISL6401 EVALUATION BOARD
BOARD NAME
ISL6401EVAL1E
IC
ISL6401CB
PACKAGE
14-Ld SOIC
The evaluation board kit also includes 5 samples of
ISL6401CB and ISL6401CR each.
Recommended Test Equipment
If a 5V supply is being used for the VCC input, place a
jumper connecting the pins to the left (pin 1 and pin 2) of
JP1. Placing a jumper to the right (pin 2 and pin 3) of JP2 will
supply the bias of the ISL6401 from the input voltage at VIN
using a zener diode (D1).
Input Voltage - Adjust the power supplies to provide the 5V
and 12V input voltages. With the power supplies turned off,
connect the positive lead of the 5V supply to the VCC post
(P3). Connect the ground lead of the supply to the GND post
(P4). Connect the positive lead of the 12V supply to the VIN
post (P1). Connect the ground lead to the GND post (P2).
Output Voltage Loading and Monitoring - To exercise and
monitor VOUT1, connect the positive lead of one of the
electronic loads to the GND post (P7). Connect the ground
lead of the electronic load to the VOUT1 post (P8). Connect
the positive end of a digital multimeter to the VOUT1 post
(P8). Connect the digital multimeter ground terminal to the
GND post (P7).
To exercise and monitor VOUT2, connect the positive lead of
the other electronic load to the GND post (P10). Connect the
ground lead of the electronic load to the VOUT1 post (P9).
Connect the positive end of a digital multimeter to the
VOUT1 post (P9). Connect the digital multimeter ground
terminal to the GND post (P10).
Each output can be viewed with an oscilloscope using the
two scope probes, SP1 (VOUT1) and SP2 (VOUT2).
Startup
The ISL6401 features an internal digital soft start to reduce
transformer and output capacitor stress and to reduce the
inrush current surge on the input circuits. Figure 1 shows the
startup sequence.
VOUT1
20V/DIV
• A 5V power supply to bias the IC.
• A 12V power supply capable of supplying 2A of current
VOUT2
20V/DIV
• Two electronic loads
• Precision digital multimeters
• A 4-channel scope with probes
Power and Load Connections
The ISL6401 evaluation board has three sets of terminal
posts and a jumper that are used to supply the input voltages
and to monitor and load the outputs.
Jumper Settings - Jumper JP1 allows the ISL6401 to be
biased from a separate 5V supply or from the input voltage
at VIN using a zener diode.
2
VIN
10V/DIV
10ms/DIV
FIGURE 1. SOFT START WAVEFORMS (2ms/DIV)
Application Note 1082
600
Output Ripple - Figure 2 shows the output voltage ripple for
VOUT1 and VOUT2 both at 100mA load.
500
FREQUENCY (kHz)
Output Performance
VOUT1
20mV/DIV
400
300
200
100
VOUT2
20mV/DIV
10us/DIV
FIGURE 2. OUTPUT 1 AND 2 RIPPLE VOLTAGE
Transient Response - Figure 3 and Figure 4 show the
transient performance of the each output for a step load from
0mA to 100mA.
VOUT1
50mV/DIV
0
82
120
180
250 300 390 510
CAPACITANCE (pF)
610
820
1200
FIGURE 5. OUTPUT SWITCHING FREQUENCY vs CT
External Synchronization - The internal oscillator can be
synchronized by an external clock connected to the SYNC
pin (P6). Program the free running frequency of the oscillator
to be 10% slower than the desired synchronous frequency.
The external clock signal should have a minimum pulse
width of 20ns.
Shutdown
When the SD pin (P5) is pulled low, the PWM is turned off
and the output capacitors discharge. A typical shutdown
waveform using the SD pin is shown in Figure 6.
IOUT1
50mA/DIV
2ms/DIV
VOUT1
20V/DIV
FIGURE 3. VOUT1 TRANSIENT RESPONSE
VOUT2
200mV/DIV
VOUT2
20V/DIV
10ms/DIV
FIGURE 6. OUTPUT SHUTDOWN WAVEFORMS
Conclusion
IOUT2
50mA/DIV
2ms/DIV
FIGURE 4. VOUT2 TRANSIENT RESPONSE
Oscillator
Switching Frequency - The gate driver output switching
frequency can be programmed from 50kHz to 600kHz by
adjusting the capacitor value on the CT pin (C5). Figure 5
can be used as a guideline in selecting the capacitor value
required for a given frequency.
3
The ISL6401EVAL1evaluation board is a flyback reference
design optimized to provide a high performance, low-cost
solution for RSLIC Ring and Talk power supplies in VoIP
application. It has the capablility of evaluating device operation
with loads that simulate one, two, three, or four line operation.
References
1. ISL6401 Datasheet, Intersil Corporation, File No. FN9007
For Intersil documents available on the web, see
http://www.intersil.com/
ISL6401EVAL1E Schematic
VIN
P1
SP1
P2
GND
VOUT1
C1A-G
2.2µF
4
R1
340
JP1
P3
VCC +5V
8
D1
BZT52C5V1
P4
GND
T1
o
o
o
o
o
PRI
2
SEC
o 7
3
C3
1µF
P5
o 6
P6
SYNC
VCC 14
1 SD
C6
180pF
C7
R7
499
TP2
NULL
E
R8
0.027µF
NFB
D2
C11
2.2µF
C13
2.2µF
GND
R9
2.4K
P8
VOUT1
MUR5120T3
4
C5
560pF
TP1
P7
+ C10A-B +
270µF
2 SYNC
PVCC 13
3 CT
GATE 12
TP3
Q1-D
5 FB
R6
1.24K
GND 10
6 NFB OUT
CS 9
7 NFB IN
NC 8
ISL6401
C8
1000pF
IFLY0012
R10
220
Q1
IRLR2905
4 COMP PGND 11
30K
o 5
R3
100
TP4
CS
R4
0.025
D3
MUR5160T3
P9
C9A
100µF
C4
330pF
C12
0.1µF
C9B
39µF
+
+
C14
0.1µF
P10
VOUT2
GND
SP2
R13
5.1
VOUT2
C15
0.01µF
R11
47.5K
R12
143K
P11
GND
Application Note 1082
SHUTDOWN
o
1
R2
10K
C2
220pF
R5
100
Application Note 1082
ISL6401EVAL1E Bill of Materials
ITEM
REFERENCE
QTY
PART NUMBER
1
U1
1
ISL6401CB
IC, Linear
Current mode PWM
Controller
2
Q1
1
IRLR2905
MOSFET Single
N-channel, 55V, 0.027Ω, 42A TO-252AA
International
3
D1
1
BZT52C5V1
Diode
Zener, 5.1V, ±5%, 0.5A
SOD123
Diode
4
D2
1
MURS120T3
Diode
Schottky, 200V, 1A
Case 403A-03
Motorola/ON Semi
5
D3
1
MURS160T3
Diode
Schottky, 600V, 1A
Case 403A-03
Motorola/ON Semi
6
T1
1
IFLY0012
Transformer
Custom Built
IFLY0012
GCI/Falco
7
C1A to C1G,
C11, C13
9
GMK325BJ225KN-T Capacitor, Ceramic
2.2µF, 20%, 35V, X7R
SM_1210
Taiyo Yuden
8
C2
1
0805YC221KAT2A
Capacitor, Ceramic,
NPO
220pF, 10%, 50V
SM_0805
AVX/Panasonic
9
C3
1
1812C105MAT2A
Capacitor, Ceramic, X7R 1µF, 20%, 50V
SM_1812
AVX
10
C4
1
1206YC331KAT2A
Capacitor, Ceramic,
NPO
330pF, 20%, 100V
SM_1206
AVX/Panasonic
11
C5
1
08055A561FAT2A
Capacitor, Ceramic,
NPO
560pF, ±1 50V
SM_0805
AVX/Panasonic
12
C6
1
0805YC181KAT2A
Capacitor, Ceramic,
NPO
180pF, 10%, 50V
SM_0805
AVX/Panasonic
13
C7
1
0805YC273KAT2A
Capacitor, Ceramic, X7R 0.027µF, 10%, 50V
SM_0805
AVX/Panasonic
14
C8
1
0805YC102KAT2A
Capacitor, Ceramic, X7R 1000pF, 5%, 50V
SM_0805
AVX/Panasonic
15
C9A
1
100MV100AX
Capacitor, Aluminum
100µF, 20%,100V
TANT-200-500 SAYNO
16
C9B
1
100MV39AX
Capacitor, Aluminum
39µF, 20%,100V
CASE-CC
SAYNO
17
C10A
1
35MV270AX
Capacitor, Aluminum
270µF, 20%,35V
CASE-CC
SAYNO
18
C10B (Do Not
Populate)
1
Capacitor, Aluminum
CASE-CC
SAYNO
19
C12, C14
2
1812C104MAT2A
Capacitor, Ceramic, X7R 0.1µF, 20%, 100V
SM_1812
AVX/Panasonic
20
C15
1
0805YC103KAT2A
Capacitor, Ceramic, X7R 0.01µF, 5%, 50V
SM_0805
AVX/Panasonic
21
R1
1
Resistor, Film
340Ω, 5%, 1/2W
SM_2010
Panasonic
22
R2
1
Resistor, Film
10kΩ, 1%, 0.1W
SM_0805
Panasonic
23
R3
2
Resistor, Film
100Ω, 5%, 0.1W
SM_0805
Panasonic
24
R4
1
Resistor, Power metal
strip
0.025Ω, 1%, 1W
SM_2512
Vishay / IRC
25
R5
1
Resistor, Film
100Ω, 5%, 0.25W
SM_1210
Panasonic
26
R6
1
Resistor, Film
1.24kΩ, 1%, 0.1W
SM_0805
Panasonic
27
R7
1
Resistor, Film
499Ω
SM_0805
Panasonic
28
R8
1
Resistor, Film
30KΩ, 1%, 0.1W
SM_0805
Panasonic
29
R9 (Do Not
Populate)
1
Resistor, Film
2.43kΩ, 1%, 1/8W
SM_01206
Panasonic
30
R10
1
Resistor, Film
220Ω, 1%, 0.25W
SM_1210
Panasonic
31
R11
1
Resistor, Film
47.5kΩ, 1%, 0.1W
SM_0805
Panasonic
32
R12
1
Resistor, Film
143kΩ, 1%, 0.1W
SM_0805
Panasonic
5
PART TYPE
DESCRIPTION
PACKAGE
SO-14
VENDOR
Intersil
Application Note 1082
ISL6401EVAL1E Bill of Materials (Continued)
ITEM
REFERENCE
QTY
33
R13
1
34
JP1
1
35
JP1
36
PART NUMBER
PART TYPE
DESCRIPTION
PACKAGE
Resistor, Film
5R1Ω, 5%, 0.25W
68000-236-1X3
Jumper, 3 position
1x3 Break Strip GOLD
1
S9001-ND
Jumper
2 pin jumper
TP1 to TP4
4
5002
TEST POINT
vertical,white
PC test jack
PTH
Keystone
37
P1 - P11
11
1514-2
Turrett Post
Terminal post,through
hole,1/4 inch tall
PTH
Keystone
38
SP1, SP2
2
TEK131-4353-00
Terminal, Scope Probe
Terminal, Scope Probe
39
Mounting Hole
1-4
4
4-40X1/2 Screw
Screw, #4, Panhead
4-40x1/2 Screw
40
Mounting Hole
1-4
4
4-40X3/4 StandoffMetal
Standoff, 1", for #4 screw 4-40x3/4 Standoff-Metal
ISL6401EVAL1E Layout
FIGURE 7. TOP SILKSCREEN
6
SM_1210
VENDOR
Panasonic
Digikey
Tektronix
PTH = 0.250"
Application Note 1082
ISL6401EVAL1E Layout (Continued)
FIGURE 8. TOP LAYER 1
FIGURE 9. TOP LAYER 2
7
Application Note 1082
ISL6401EVAL1E Layout (Continued)
FIGURE 10. TOP LAYER 3
FIGURE 11. BOTTOM SILKSCREEN
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
8