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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 55A 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/
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 200 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 200, 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 Output Power Efficiency Output Voltages -24V Requirements (4 lines) REQUIREMENT 5 or 12 volts 3 to 10 watts 80 to 90% -24V, -72 to -100V and/or -48V Regulation: 5% Maximum Output Current: 0.10A Ripple: Less than 0.25Vpp Regulation: 10% Maximum Output Current: 0.10A Ripple: Less than 1Vpp
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 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
-72V Requirements (4 lines)
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright (c) Intersil Americas Inc. 2003. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
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
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
The evaluation board kit also includes 5 samples of ISL6401CB and ISL6401CR each.
Recommended Test Equipment
* A 5V power supply to bias the IC. * A 12V power supply capable of supplying 2A of current * Two electronic loads * Precision digital multimeters * A 4-channel scope with probes
VOUT2 20V/DIV
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.
VIN 10V/DIV 10ms/DIV
FIGURE 1. SOFT START WAVEFORMS (2ms/DIV)
2
Application Note 1082
Output Performance
Output Ripple - Figure 2 shows the output voltage ripple for VOUT1 and VOUT2 both at 100mA load.
FREQUENCY (kHz) 10us/DIV 600 500 400 300 200 100 VOUT2 20mV/DIV 0
VOUT1 20mV/DIV
82
120
180
FIGURE 2. OUTPUT 1 AND 2 RIPPLE VOLTAGE
250 300 390 510 CAPACITANCE (pF)
610
820
1200
FIGURE 5. OUTPUT SWITCHING FREQUENCY vs CT
Transient Response - Figure 3 and Figure 4 show the transient performance of the each output for a step load from 0mA to 100mA.
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.
VOUT1 50mV/DIV
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 GND P2 P3 P4 C1A-G 2.2F JP1 D1 BZT52C5V1 8 o PRI R2 10K P5 P6 C5 560pF 1 SD C6 180pF C7 0.027F E R8 30K 2 SYNC 3 CT 5 FB 6 NFB OUT R6 1.24K 7 NFB IN ISL6401 VCC 14 PVCC 13 GATE 12 GND 10 CS 9 NC 8 C8 1000pF R3 100 TP3 Q1-D Q1 IRLR2905 R13 5.1 C15 0.01F 1 C3 1F o o o o o T1 2 SEC o7 3 o6 4 o5 IFLY0012 R10 220 D3 MUR5160T3 C9A 100F C4 330pF + C9B 39F + C12 0.1F C14 0.1F P9 + C10A-B + 270F C11 2.2F C13 2.2F R9 2.4K P8 VOUT1 VOUT1 R1 340 R5 100 C2 220pF
4
VCC +5V GND SHUTDOWN SYNC R7 499 TP1 NFB TP2 NULL
P7
GND
D2
MUR5120T3
Application Note 1082
VOUT2
P10
GND
4 COMP PGND 11
SP2 VOUT2
TP4 CS R4 0.025
R11 47.5K
R12 143K
P11
GND
Application Note 1082 ISL6401EVAL1E Bill of Materials
ITEM 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 REFERENCE U1 Q1 D1 D2 D3 T1 C1A to C1G, C11, C13 C2 C3 C4 C5 C6 C7 C8 C9A C9B C10A C10B (Do Not Populate) C12, C14 C15 R1 R2 R3 R4 R5 R6 R7 R8 R9 (Do Not Populate) R10 R11 R12 QTY 1 1 1 1 1 1 9 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1812C104MAT2A 0805YC103KAT2A PART NUMBER ISL6401CB IRLR2905 BZT52C5V1 MURS120T3 MURS160T3 IFLY0012 PART TYPE IC, Linear MOSFET Single Diode Diode Diode Transformer DESCRIPTION Current mode PWM Controller PACKAGE SO-14 VENDOR Intersil International Diode Motorola/ON Semi Motorola/ON Semi GCI/Falco Taiyo Yuden AVX/Panasonic AVX AVX/Panasonic AVX/Panasonic AVX/Panasonic AVX/Panasonic AVX/Panasonic
N-channel, 55V, 0.027, 42A TO-252AA Zener, 5.1V, 5%, 0.5A Schottky, 200V, 1A Schottky, 600V, 1A Custom Built 2.2F, 20%, 35V, X7R 220pF, 10%, 50V SOD123 Case 403A-03 Case 403A-03 IFLY0012 SM_1210 SM_0805 SM_1812 SM_1206 SM_0805 SM_0805 SM_0805 SM_0805
GMK325BJ225KN-T Capacitor, Ceramic 0805YC221KAT2A 1812C105MAT2A 1206YC331KAT2A 08055A561FAT2A 0805YC181KAT2A 0805YC273KAT2A 0805YC102KAT2A 100MV100AX 100MV39AX 35MV270AX Capacitor, Ceramic, NPO
Capacitor, Ceramic, X7R 1F, 20%, 50V Capacitor, Ceramic, NPO Capacitor, Ceramic, NPO Capacitor, Ceramic, NPO 330pF, 20%, 100V 560pF, 1 50V 180pF, 10%, 50V
Capacitor, Ceramic, X7R 0.027F, 10%, 50V Capacitor, Ceramic, X7R 1000pF, 5%, 50V Capacitor, Aluminum Capacitor, Aluminum Capacitor, Aluminum Capacitor, Aluminum Capacitor, Ceramic, X7R 0.1F, 20%, 100V Capacitor, Ceramic, X7R 0.01F, 5%, 50V Resistor, Film Resistor, Film Resistor, Film Resistor, Power metal strip Resistor, Film Resistor, Film Resistor, Film Resistor, Film Resistor, Film Resistor, Film Resistor, Film Resistor, Film 340, 5%, 1/2W 10k, 1%, 0.1W 100, 5%, 0.1W 0.025, 1%, 1W 100, 5%, 0.25W 1.24k, 1%, 0.1W 499 30K, 1%, 0.1W 2.43k, 1%, 1/8W 220, 1%, 0.25W 47.5k, 1%, 0.1W 143k, 1%, 0.1W 100F, 20%,100V 39F, 20%,100V 270F, 20%,35V
TANT-200-500 SAYNO CASE-CC CASE-CC CASE-CC SM_1812 SM_0805 SM_2010 SM_0805 SM_0805 SM_2512 SM_1210 SM_0805 SM_0805 SM_0805 SM_01206 SM_1210 SM_0805 SM_0805 SAYNO SAYNO SAYNO AVX/Panasonic AVX/Panasonic Panasonic Panasonic Panasonic Vishay / IRC Panasonic Panasonic Panasonic Panasonic Panasonic Panasonic Panasonic Panasonic
5
Application Note 1082 ISL6401EVAL1E Bill of Materials (Continued)
ITEM 33 34 35 36 37 38 39 40 REFERENCE R13 JP1 JP1 TP1 to TP4 P1 - P11 SP1, SP2 Mounting Hole 1-4 Mounting Hole 1-4 QTY 1 1 1 4 11 2 4 4 68000-236-1X3 S9001-ND 5002 1514-2 TEK131-4353-00 4-40X1/2 Screw 4-40X3/4 StandoffMetal PART NUMBER PART TYPE Resistor, Film Jumper, 3 position Jumper TEST POINT vertical,white Turrett Post Terminal, Scope Probe Screw, #4, Panhead DESCRIPTION 5R1, 5%, 0.25W 1x3 Break Strip GOLD 2 pin jumper PC test jack Terminal post,through hole,1/4 inch tall Terminal, Scope Probe 4-40x1/2 Screw PTH = 0.250" PTH PTH Digikey Keystone Keystone Tektronix PACKAGE SM_1210 VENDOR Panasonic
Standoff, 1", for #4 screw 4-40x3/4 Standoff-Metal
ISL6401EVAL1E Layout
FIGURE 7. TOP SILKSCREEN
6
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

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