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. 1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright © 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 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