AN1082 INTERSIL | Alldatasheet
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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. Using the ISL6401 RSLIC PWM Controller Evaluation Board 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. 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. 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
“ready to use” right from the box. The IC requires +5V Bias. section is then stacked on the -24V section to get the -72V. based on load condition on both outputs. ISL6401CB and ISL6401CR each.
- 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 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. 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.
TABLE 2. ISL6401 EVALUATION BOARD FIGURE 1. SOFT START WAVEFORMS (2ms/DIV)
2.2µF oooooo 1µF GND P3VCC +5V o o o R10 220 C4 330pF MUR5160T3 7 8 SD SYNC CT COMP FB NFB OUT NFB IN VCC PVCC GATE PGND GND CS NC ISL6401 GND + C10A-B 270µF MUR5120T3 R11 47.5K IFLY0012 SEC VOUT1 VOUT2 0.025 100 IRLR2905 1000pF 180pF 0.027µF 30K 499 R6 1.24K E 560pF PRI C9A 100µF C12 0.1µF C11 2.2µF R12 143K C14 0.1µF C13 2.2µF 2.4K 100 220pF TP4 CS C9B 39µF R13 5.1 TP3 Q1-D 340 BZT52C5V1 10K TP1 NFB P6SYNC SHUTDOWN JP1 P2GND GNDP11 P10 SP2 VOUT2 SP1 VOUT1 GND TP2 NULL C15 0.01µF
ISL6401EVAL1E Bill of Materials ITEM REFERENCE QTY PART NUMBER PART TYPE DESCRIPTION PACKAGE VENDOR
1 U1 1 ISL6401CB IC, Linear Current mode PWM
2 Q1 1 IRLR2905 MOSFET Single N-channel, 55V, 0.027 Ω, 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
7C 1 A t o C 1 G , C11, C13 9 GMK325BJ225KN-T Capacitor, Ceramic 2.2µF, 20%, 35V, X7R SM_1210 Taiyo Yuden
8 C2 1 0805YC221KAT2A Capacitor, Ceramic,
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,
330pF, 20%, 100V SM_1206 AVX/Panasonic
11 C5 1 08055A561FAT2A Capacitor, Ceramic,
560pF, ±1 50V SM_0805 AVX/Panasonic
12 C6 1 0805YC181KAT2A Capacitor, Ceramic,
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, Alumi num 100µF, 20%,100V TANT-200-500 SAYNO
16 C9B 1 100MV39AX Capacitor, Alum inum 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 340 Ω, 5%, 1/2W SM_2010 Panasonic
22 R2 1 Resistor, Film 10k Ω, 1%, 0.1W SM_0805 Panasonic 23 R3 2 Resistor, Film 100 Ω, 5%, 0.1W SM_0805 Panasonic
24 R4 1 Resistor, Power metal
0.025Ω, 1%, 1W SM_2512 Vishay / IRC 25 R5 1 Resistor, Film 100 Ω, 5%, 0.25W SM_1210 Panasonic 26 R6 1 Resistor, Film 1.24k Ω, 1%, 0.1W SM_0805 Panasonic
27 R7 1 Resistor, Film 499 Ω SM_0805 Panasonic
28 R8 1 Resistor, Film 30K Ω, 1%, 0.1W SM_0805 Panasonic
29 R9 (Do Not
Populate) 1 Resistor, Film 2.43k Ω, 1%, 1/8W SM_01206 Panasonic 30 R10 1 Resistor, Film 220 Ω, 1%, 0.25W SM_1210 Panasonic 31 R11 1 Resistor, Film 47.5k Ω, 1%, 0.1W SM_0805 Panasonic 32 R12 1 Resistor, Film 143k Ω, 1%, 0.1W SM_0805 Panasonic Application Note 1082
34 JP1 1 68000-236-1X3 Jumper, 3 position 1x3 Break Strip GOLD
35 JP1 1 S9001-ND Jumper 2 pin jumper Digikey
36 TP1 to TP4 4 5002 TEST POINT
37 P1 - P11 11 1514-2 Turrett Post Terminal post,through
38 SP1, SP2 2 TEK131-4353-00 Terminal, Scope Probe Terminal, Scope Probe Tektronix
39 Mounting Hole
40 Mounting Hole
FIGURE 7. TOP SILKSCREEN