an1082

Using the ISL6401 RSLIC PWM Controller
Evaluation Board
®
Application Note
January 30, 2009
AN1082.2
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 overcurrent
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 (“ISL6401: Synchronizing Current
Mode PWM for Subscriber Line Interface Circuits”), Intersil
Corporation, FN9007, available on Intersil’s website,
http://www.intersil.com/data/fn/fn9007.pdf
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.
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 has created
the need to control and manage the functions of the phone
locally as opposed to the central office. In both instances the
1
principals governing the operation of the phone loop are
essentially the same.
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 -70V 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 20mA to 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 listed in the following table are for a 4-line
requirement with 5 REN per line.
TABLE 1. TYPICAL POWER SUPPLY REQUIREMENT FOR
VoIP RESIDENTIAL GATEWAY
PARAMETER
REQUIREMENT
Input Voltage
5V or 12V
Output Power
3W to 10W
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 0.25VP-P
-72V Requirements (4 lines)
Regulation: ±10% Maximum
Output Current: 0.10A Ripple:
Less than 1VP-P
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2003, 2005, 2009. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
Application Note 1082
Using the ISL6401EVAL1Z Evaluation Board
The ISL6401EVAL1Z Schematic shows a current mode
power supply using the Intersil ISL6401 in standard flyback
topology. The ISL6401EVAL1Z 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 0mA to 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. ISL6401EVAL1Z EVALUATION BOARD
BOARD NAME
ISL6401EVAL1Z
IC
ISL6401CBZ
PACKAGE
14 Ld SOIC
The evaluation board kit also includes 5 samples of
ISL6401CBZ and ISL6401CRZ 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).
Start-up
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
start-up 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 ISL6401EVAL1Z 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)
AN1082.2
January 30, 2009
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
10µs/DIV
FIGURE 2. OUTPUT 1 AND 2 RIPPLE VOLTAGE
Transient Response - Figures 3 and 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
The ISL6401EVAL1Z evaluation 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 capability of evaluating device operation
with loads that simulate one, two, three, or four line operation.
Oscillator
References
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.
1. ISL6401 Datasheet (“ISL6401: Synchronizing Current
Mode PWM for Subscriber Line Interface Circuits”), Intersil
Corporation, FN9007. For Intersil documents available on
the web, see http://www.intersil.com/
3
AN1082.2
January 30, 2009
ISL6401EVAL1Z 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
VCC 14
1 SD
C6
180pF
C7
R7
499
TP2
NULL
E
R8
0.027µF
NFB
C11
2.2µF
GND
R9
2.4k
P8
VOUT1
o 6
4
C5
560pF
TP1
D2
C13
2.2µF
MUR5120T3
P6
SYNC
P7
+ C10A-B +
270µF
2 SYNC
PVCC 13
3 CT
GATE 12
TP3
o 5
Q1-D
IFLY0012
R10
220
Q1
IRLR2905
4 COMP PGND 11
30k
5 FB
R6
1.24k
GND 10
6 NFB OUT
CS 9
7 NFB IN
NC 8
ISL6401
C8
1000pF
R3
100
TP4
CS
R4
0.025
D3
MUR5160T3
P9
C9A
100µF
C4
330pF
C12
0.1µF
C9B
39µF
+
VOUT2
C14
0.1µF
P10
+
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
AN1082.2
January 30, 2009
Application Note 1082
ISL6401EVAL1Z Bill of Materials
REFERENCE
DESIGNATOR
QTY
1
DESCRIPTION
PWB-PCB, ISL6401EVAL1Z, REVA, SOIC, ROHS
MANUFACTURER
PART
MANUFACTURER
TITAN
ISL6401EVAL1ZREVAPCB
1
C9A
CAP, RADIAL, 10µF,100V, 20%, AL E, ROHS
SANYO
100ME100AX
1
C9B
CAP, RADIAL, 39µF, 100V, 20%, AL ELEC, ROHS
SANYO
100ME39AX
1
C10A
CAP, RADIAL, 10x16, 270µF, 35V, 20%, AL.EL., ROHS
SANYO
35ME270AX
1
C8
CAP, SMD, 0805, 1000pF, 50V, 5%, NPO, ROHS
PANASONIC
ECU-V1H102JCX
1
C15
CAP, SMD, 0805, 0.01µF, 50V, 5%, X7R, ROHS
VENKEL
C0805X7R500-103JNE
1
C6
CAP, SMD, 0805, 180pF, 50V, 5%, NPO, ROHS
VENKEL
C0805COG500-181JNE
1
C2
CAP, SMD, 0805, 220pF, 50V, 10%, X7R, ROHS
VENKEL
C0805X7R500-221KNE
1
C7
CAP, SMD, 0805, 0.027µF, 50V, 10%, X7R, ROHS
1
C5
CAP, SMD, 0805, 560pF, 50V, 5%, NPO, ROHS
MINI-REEL
605-356
1
C4
CAP, SMD, 1206, 330pF, 100V, 5%, NPO, ROHS
VENKEL
C1206COG101-331JNE
9
C1A-C1G, C11, C13
CAP, SMD, 1210, 2.2µF, 50V, 10%, X7R, ROHS
TDK
C3225X7R1H225K
2
C12, C14
CAP, SMD, 1812, 0.1µF, 100V, 20%, X7R, ROHS
VENKEL
C1812X7R101-104MNE
1
C3
CAP, SMD, 1812, 1µF, 50V, 10%, X7R, ROHS
VENKEL
C1812X7R500-105KNE
2
SP1, SP2
CONN-GEN, SHIELDED TEST JACK, VERTICAL, ROHS
JOHNSON
COMPONENTS
129-0701-202
10
P1-P10
CONN-TURRET, TERMINAL POST, TH, ROHS
KEYSTONE
1514-2
4
TP1-TP4
CONN-MINI TEST POINT, VERTICAL, WHITE, ROHS
KEYSTONE
5002
1
JP1
CONN-HEADER, 1x3, BRKAWY 1x36, 2.54mm, ST
BERG/FCI
68000-236-1X3
1
JP1
(place on pin 1 and 2)
CONN-JUMPER, SHORTING, 2PIN, BLACK, GOLD, ROHS
SULLINS
SPC02SYAN
1
D1
DIODE-ZENER, SMD, SOD-123, 5.1V, 500mW, ROHS
DIODES, INC.
BZT52C5V1-7-F
1
D2
DIODE-RECTIFIER, SMD, SMB, 2P, 1A, 200V, ROHS
ON SEMICONDUCTOR
MURS120T3G
1
D3
DIODE-RECTIFIER, SMD, SMB, 2P, 1A, 600V, ROHS
ON SEMICONDUCTOR
MURS160T3G
5
PURCHASE, DNP. BAG
AND SHIP W/BOARD.
IC-RSLIC PWM, 14P, SOIC, ROHS
INTERSIL
ISL6401CBZ
1
U1
IC-RSLIC PWM, 14P, SOIC, ROHS
INTERSIL
ISL6401CBZ
5
PURCHASE, DNP. BAG
AND SHIP W/BOARD.
IC-RSLIC PWM CONTROLLER, 16P, QFN, 4x4, ROHS
INTERSIL
ISL6401CRZ
1
Q1
TRANSIST-MOS, N-CHANNEL, SMD, D-PAK, 42A, ROHS
INTERNATIONAL
RECTIFIER
IRLR2905PBF
1
R3
RESISTOR, 0805, 100Ω, 1/8W, 1%, TF, ROHS
VENKEL
CR0805-8W-1000FT
1
R2
RES, SMD, 0805, 10k, 1/8W, 1%, TF, ROHS
VENKEL
CR0805-8W-1002FT(PbFREE)
1
R6
RES, SMD, 0805, 1.24k, 1/8W, 1%, TF, ROHS
PANASONIC
ERJ-6ENF1241V
1
R12
RES, SMD, 0805, 143k, 1/8W, 1%, TF, ROHS
PANASONIC
ERJ-6ENF1433V
1
R8
RES, SMD, 0805, 30k, 1/8W, 1%, TF, ROHS
1
R11
RES, SMD, 0805, 47.5k, 1/8W, 1%, TF, ROHS
KOA
RK73H2AT4752F
1
R7
RES, SMD, 0805, 499Ω, 1/8W, 1%, TF, ROHS
YAGEO
RC0805FR-07499RL
1
R5
RES, SMD, 1206, 100Ω, 1/4W, 1%, TF, ROHS
STACKPOLE
RMC1/8 100R 1% T/R
1
R10
RES, SMD, 1206, 220Ω, 1/4W, 5%, TF, ROHS
VISHAY
CRCW1206221J
1
R13
RES, SMD, 1210, 5.1Ω, 1/4W, 5%, TF, ROHS
PANASONIC
ERJ-14YJ5R1U
1
R4
RES, SMD, 2512, 0.025Ω, 1W, 1%, TF, ROHS
DALE
WSL-2512-.0251%
1
R1
RES, SMD, 2010, 332Ω, 1/2W, 1%, TF, ROHS
PANASONIC
ERJ-12SF3320U
5
AN1082.2
January 30, 2009
Application Note 1082
ISL6401EVAL1Z Bill of Materials (Continued)
REFERENCE
DESIGNATOR
QTY
DESCRIPTION
1
T1
TRANSFORMER-FLYBACK, 6.0µH, 10%, SMD, 8P, 25x17,
ROHS
4
Four corners.
SCREW, 4-40x1/2in, PAN, NYLON, PHILLIPS, ROHS
4
Four corners.
1
0
0
1
MANUFACTURER
PART
MANUFACTURER
GCI TECHNOLOGIES
IFLY0012/G013064LF
STANDOFF, 4-40x3/4in, F/F, HEX, NYLON
KEYSTONE
1902D
Place assy in bag
BAG, STATIC, 5x8, ZIP LOC
INTERSIL
212403-013
C10B
DO NOT POPULATE OR PURCHASE
R9
DO NOT POPULATE OR PURCHASE
LABEL, FOR SERIAL NUMBER AND BOM REV #
ISL6401EVAL1Z Layout
Z
FIGURE 7. TOP SILKSCREEN
6
AN1082.2
January 30, 2009
Application Note 1082
ISL6401EVAL1Z Layout (Continued)
FIGURE 8. TOP LAYER 1
FIGURE 9. TOP LAYER 2
7
AN1082.2
January 30, 2009
Application Note 1082
ISL6401EVAL1Z Layout (Continued)
FIGURE 10. TOP LAYER 3
FIGURE 11. BOTTOM SILKSCREEN
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 the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
8
AN1082.2
January 30, 2009