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| AN716 Vishay Siliconix Designing with Siliconix PC Card (PCMCIA) Power Interface Switches INTRODUCTION PC CARD POWER SWITCHING: AN OVERVIEW Upon initial card insertion, the PC Card interface must determine its required supply voltages and wake up the card with the proper voltages supplied. The purpose of the PC Card power selector function is therefore that of a power multiplexer, as shown in Figure 1. The switch configuration has been designed for the VPP output to select among all the available voltages (a four-state output), namely 12, 5, and 3.3 V along with ground (0 V). The VCC line is a higher-current three-state output for 5- and 3.3-V circuitry, which also can provide a grounded condition. Innovation in portable computer design is driven today by the need for smaller, lighter, and more energy-efficient products. This has been the driving force behind the small form-factor I/O cards that have created an emerging market for PC Cards. In the current version of the PC Card standard, a computer or other "host platform" must be able to deliver some combination of 3.3, 5, and 12 V at the slot for a card to operate. These voltages are then supplied to the card on two supply lines called VCC and VPP . Vishay Siliconix offers a series of integrated power MOSFETs specifically designed for the strict demands of the PC Card power interface. The, Si9711CY, and Si9712DY devices switch 3.3 V or 5 V to Vcc and 3 V, 5 V, or 12 V to the flash memory program pin, VPP . The Si9706DY and Si9707DY are a functional subset of the Si9712DY. They support only the Vcc line for systems that use VPP from the main supply or future specialized systems that do not support the VPP function. VOLTAGE REQUIREMENTS AND REVERSE BLOCKING CAPABILITY The power switch requirements in the PC Card voltage selector are unique for at least four reasons. First, the power selector's control interface must follow the PC Card communication format (and interface conveniently to PC Card controller ICs). While the control signals from the interface chip are 3- or 5-V CMOS logic, the 12-V signals must be controlled from this lower voltage input using level shifting. Second, the switches must be bidirectionally blocking since any one of the supplies may go to sleep and short to ground. If the output is held high by another switch, the input is then at a lower potential than the output. One example of this condition is where S1 is off and S2 (as shown in Figure 3 and Figure 4) is on so that VPP is biased to the same potential as VCC. In the event that the 12-V input drops and the supply sleeps, S1 changes from a state where its input voltage exceeds its output to the opposite polarity. Similar cases can occur with S3 and S4. Address Bus The Si97XX series of PC Card power interface switches is intended for battery-operated notebook, sub-notebook, and palmtop computers. These monolithic power ICs provide several options for any host platform power switching application. In a single surface-mount package, they provide tighter output tolerances because of their low on-resistance rating, and longer battery life, with leakage currents of less than 1 mA. Data/Control Bus PC Card Controller Power Control VPP VCC PC Card Slot Si9711CY, or Si9712DY +12 V Host Platform Power Supply +5 V +3.3 V FIGURE 1. Function of Power Selector for PC Cards Document Number: 70587 14-Nov-97 www.vishay.com S FaxBack 408-970-5600 1 AN716 Vishay Siliconix LOW ON RESISTANCE ISSUES The third unique aspect of the PC Card voltage selector function is the need for low on-resistance switches, generally below 200 mW on the VPP = 12 V switch and even as low as 60 mW on the 3.3-V switch. The low on-resistance is not necessarily needed for reasons of power dissipation or high current, but rather to prevent significant voltage drops across the switch. In general, the input to the switch from the system supply may be 4% below nominal, leaving only one percent for the switch. The PC Card standard specifies a maximum variation of "5% on both VCC and VPP . This structure is clearly driven by Flash RAM requirements on VPP and the tight rail voltage on 3.3-V ICs. Therefore, the system designer must consider the allowable voltage drop for a maximum expected current on both VCC and VPP. For a 500-mA load at 5 V on VCC, a 1% voltage drop requires a maximum on-resistance of 100 mW . The Si9712DY exceeds this requirement over the full temperature range (-40 to 85_C). Assuming a slightly lower current requirement at 3.3 V, the Si9712DY meets 1% voltage drop over the operating temperature range with a maximum specified on-resistance of 80 mW. Because of Vishay Siliconix' pioneering efforts in battery disconnect switches, the PC Card power selector function has been integrated monolithically using the proprietary BCD15 technology. This integrated function actually replaces seven to nine discrete power MOSFETs per slot beyond those involved in the interface and level shifting circuitry. communications cards. For the sake of this discussion, we will group these higher-power systems together as the notebooks. If a host platform power supply can only handle a certain peak current, then it should control the ramp to support that limit over the range of available cards. Unfortunately, the growing number of card vendors makes the card load a difficult parameter to define without extensive research. According to ongoing surveys of card manufacturers contacted by Vishay Siliconix, this capacitance can be as high as 150 mF. Indeed, cards can be grouped in at least two categories: high-power cards that can have as much as 150-mF bypass on VCC, and low-power cards that are well below a 50-mF bypass on VCC. With these parameters in mind, it is clear from Figure 2 that the host platform with a surge current capability in the milliamp range would need to support a ramp in the low millisecond range for the most reliable operation over the full range of cards. 10 150 mF @ 5 V Current (A) 150 mF @ 3.3 V 1 50 mF @ 5 V 50 mF @ 3.3 V CONTROLLING THE POWER UP The fourth unique aspect of the PC Card power selector is its need for controlled slew rates on the 3.3-V and 5-V switches. The requisite switching times range from hundreds-of-microseconds to milliseconds: extremely long intervals for integrated circuit technology. Because of the versatility of our BCD15 technology, however, Vishay Siliconix can control the power device behavior over such long intervals. Designers face a dilemma when dealing with switching ramp times. On the one hand, fast rise times are directly related to the current spikes that can shut down some host platforms. Even the capacitors on PC cards themselves can be damaged by surge currents. Yet some designers correctly wonder whether the ramp time called out by the PC Card Rev. 2.1 standard, as slow as 300 ms, is actually so slow as to latch up and draw excessive current. The rules in this area are different for different types of host platforms. The small handheld systems that operate off A-cells cannot supply the current to support a fast ramp to a large load. In fact, many of these palmtops attempt to avoid the issue by not offering a Type III slot (although some Type II cards can be categorized as high-power cards). The larger portables have what it takes to supply power to a wider range of cards such as rotating media and the more powerful multimedia or wireless www.vishay.com S FaxBack 408-970-5600 0.1 0 0.001 0.002 0.003 0.004 0.005 Time (sec) FIGURE 2. Host Platform SOA Curves The curves in Figure 2 show the safe operating area based on a worst-case assumption of 150-mF card capacitance on VCC. These curves are based on the following calculation: i = C(dv/dt) + Isteady state where Isteady state is estimated at 100 mA for 5 V and 70 mA for 3.3 V during the time before the CIS register is read. A 2-ms ramp time is an ideal ramp for a platform that can support a 500-mA surge over the range of card capacitance values. The notebook category of platforms can tolerate a ramp less than 1 ms. SI9711CY A host platform design that can support a surge of close to 4 A can comfortably use the Si9711CY, which ramps at 200 ms. However, those systems that cannot tolerate this kind of peak current will be better off with the Si9712DY, which maintains a ramp closer to 1 ms. The Si9706DY and Si9707DY are modelled after the Si9712DY, and therefore support the slower ramp. Document Number: 70587 14-Nov-97 2 AN716 Vishay Siliconix PIN DESCRIPTION FOR SI9711CY S1, S2, S3, S4 (Pins 15, 16, 1, 2) +12 VIN SW1 VPP SW2 VPP SW3 +5 VIN SW4 +3.3 VIN +3.3 VIN VCC VCC VCC VCC S4 S3 GND Control input for selecting appropriate outputs on both VCC and VPP . These four inputs are CMOS compatible and can accommodate 3.3-V and 5-V rails by connecting VL to the appropriate rail voltage. Each control pin (S1, S2, S3, and S4) individually controls its respective switch (SW1, SW2, SW3, and SW4). VL (Pin 14) VL This pin is an input to indentify the rail voltage for the control inputs. Connect VL to the same rail voltage of the PC Card controller for signal voltage compatibility. +3.3 VIN (Pins 9 and 10) These pins are the input to provide +3.3 V to the VCC pins of the slot by way of Switch 4, and to VPP by way of Switch 2. Connect these pins to the host platform +3.3-V supply. +5 VIN (Pin 11) This pin is the input to provide +5 V to the VCC pins of the slot by way of Switch 3, and to Vpp by way of Switch 2. Connect this pin to the host platform +5-V supply. +12 VIN (Pin 13) This pin is the input to provide +12 V to the slot VPP by way of Switch 1. The +12 VIN pin is also used to generate the internal gate drive voltage; therefore, it is important that +12 V is continuous. Connect this pin directly to the host platform +12-V supply. See the section on suspend mode operation for non-continuous 12-V systems. VCC (Pins 6,7,8,12) PC Card slot supply voltage. Connect all four pins together and to pins 17 and 51 of the PC Card slot. Vpp (Pins 4 and 5) PC Card program and peripheral voltage to slot. Connect both pins together and to pins 18 and 52 of the PC Card slot. GND (Pin 3) Ground reference connection. Connect this pin to host platform system ground. Document Number: 70587 14-Nov-97 S1 S2 Level Shift and Drivers FIGURE 3. Si9711CY Functional Block Diagram TABLE 1. SI9711CY TRUTH TABLE S1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 S2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 S3 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 S4 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 VPP HiZ HiZ HiZ HiZ HiZ 3.3 V 5V VCC HiZ 12 V 12 V 12 V Invalid State Invalid State Invalid State Invalid State VCC HiZ 3.3 V 5V Invalid State HiZ 3.3 V 5V Invalid State HiZ 3.3 V 5V Invalid State HiZ Invalid State Invalid State Invalid State SI9712DY The Si9712DY is functionally similar to the Si9711CY with added features. The upgraded configuration of the Si9712DY provides a zero voltage output on VCC and VPP , programmable ramp time on VCC , and meets the PC Card revision 3 PC Card specification scheduled for release in January 1995. Most importantly, it offers better on-resistance in the same package style. www.vishay.com S FaxBack 408-970-5600 3 AN716 Vishay Siliconix Portable system designers who are interested in maintaining the VCC "5% tolerance called out in the PC Card standard will find Si9712DY the best choice. It is designed to support slots intended for "high-power" cards requiring more than an ampere of surge current during normal operation. Some cards that are considered "high-power" cards include rotating media, multimedia, and some wireless communication cards. The Si9712DY also appeals to the system designer because of the easy interface with the variety of industry-standard controllers. The control inputs for VCC can be configured as active high or active low by simply swapping S3 and S4. Table 2 shows that (1, 1) and (0, 0) on S3, S4 both yield zero out of VCC. Therefore, crossing control lines for SW3 and SW4 will simply change the polarity of the control. System designers using custom PC Card controllers that are pin constrained may consider tying S2 control high. The Si9712DY truth table (Table 2) shows that S1 will dominate. This limits the operation of the interface by not allowing a state for zero on VPP while VCC is active. VCC (Pin 5, 6, 7, 13) PC Card slot supply voltage. Connect all four pins together and to pins 17 and 51. VPP (Pin 3 and 4) PC Card program and peripheral voltage to slot. Connect both pins together and to pins 18 and 52. SR (Pin 16) Connect a capacitor to the SR pin to adjust the slew rate of the VCC ramp. Recommended capacitance value is identified in the data sheet. This capacitor can be omitted for designs that can tolerate the faster ramp as shown in the Si9712DY data sheet curves. GND (Pin 1) Ground reference connection. Connect this pin to the host platform system ground. PIN DESCRIPTION FOR THE SI9712DY S1, S2, S3, S4 (Pins 8, 9, 15, 2) SW1 Control input for selecting appropriate outputs on both VCC and VPP . These four inputs are CMOS compatible and can accommodate 3.3-V and 5-V rails. Each control pin (S1, S2, S3, and S4) individually controls its respective switch (SW1, SW2, SW3, and SW4). +3.3 VIN (Pins 10 and 11) +12 VIN SW2 VPP VPP SW5 VCC* VCC* SW4 +3.3 VIN +3.3 VIN SR VCC* VCC* +5 VIN SW3 These pins are the input to provide +3.3 V to the VCC pins of the slot by way of Switch 4, and to VPP by way of Switch 2. Connect these pins to the host platform +3.3-V supply. +5 VIN (Pin 12) This pin is the input to provide +5 V to the VCC pins of the slot by way of Switch 3, and to VPP by way of Switch 2. The +5 V pin is also used to generate the internal gate drive voltage; therefore, it is important that +5 V is continuous. Connect this pin to the host platform +5-V supply. See also the section on advanced sleep modes. +12 VIN (Pin 14) This pin is the input to provide +12 V to the VPP of the slot by way of Switch 1. Connect this pin directly to the host platform +12-V supply. SW6 S1 Switch Logic, Level Shift, and Drivers S2 S4 S3 GND * Externally Connect On PCB FIGURE 4. Si9712DY Functional Block Diagram www.vishay.com S FaxBack 408-970-5600 4 Document Number: 70587 14-Nov-97 AN716 Vishay Siliconix TABLE 2. SI9712DY TRUTH TABLEa S1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 S2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 S3 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 S4 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 VPP (V) 0 0 0 0 0 3.3 5 0 0 12 12 0 0 12 12 0 VCC (V) 0 3.3 5 0 0 3.3 5 0 0 3.3 5 0 0 3.3 5 0 +5 VINA S1 S2 SR +3.3 VIN +5 VIN SW1 SW2 VCC VCC SW3 Switch Logic, Level Shift and Drivers GND FIGURE 5. Si9706DY Functional Block Diagram S1A VCC S2A VCC NOTE: a. Shaded lines are error conditions for P.C. Card applications, however, switches default to the states shown. +3.3 VINA S3A S1A S2A Level Shift and Drivers SI9706DY AND SI9707DY The Si9706DY and Si9707DY are interface switches that support only the VCC pins of the PC Card interface. They are intended for systems that support the Vpp programming voltage at the main supply such as the Maxim MAX783 dc-to-dc controller shown in Figure 7. SRA S1B VCC S2B +3.3 VINB S1B S2B SRB VCC +5 VINB Level Shift and Drivers S3B The Si9706DY is a single VCC power interface switch in an 8-pin SOIC package that switches 3.3 V, 5 V, or 0 V to the VCC pins of the PC Card slot. The Si9707DY is an SO-16 that is equivalent to two Si9706DYs. Both devices have the slow VCC ramptime and smart switching featured in the Si9712DY. The simplified truth table for the Si9706DY and Si9707DY is shown in Table 3. GND FIGURE 6. Si9707DY Functional Block Diagram PIN DESCRIPTION FOR THE SI9706DY/9707DY S1, S2: TABLE 3. SI9706DY/07DY TRUTH TABLE S1 0 0 1 1 S2 0 1 0 1 VCC 0V 3.3 V 5V 0V (Si9706DY: Pin 4, 5) (Si9707DY: Pin 15, 2, 10, 7) Control input for selecting appropriate outputs on VCC. These two inputs are CMOS compatible and can accommodate 3.3-V and 5-V rails by setting VL. Table 3 shows VCC output for all states on S1 and S2. For PC Card controllers with active low control signals, S1 and S2 can be reversed. Document Number: 70587 14-Nov-97 www.vishay.com S FaxBack 408-970-5600 5 AN716 Vishay Siliconix +3.3 VIN (Si9706DY: Pin 6) (Si9707DY: Pin 11, 14) This pin is the input for +3.3 V to be connected to VCC by way of Switch 2. Connect this pin to the host platform +3.3-V supply. +5 VIN However, host platforms that turn off the +12-V supply can still use the Si9711CY with the simple external circuit shown in Figure 8. PC Card Controller PC Card Slot 5.0 +12 V System Supply Suspend 0.1 mF 1N4148 (Si9706DY: Pin 7) (Si9707DY: Pin 12, 13) This pin is the input for +5 V to be connected to Vcc by way of Switch 1. Connect this pin to the host platform +5-V supply. VCC +12 VIN +5 VIN VPP 4.7 kW 0.01 mF 1N4148 +5-V System Supply +3-V System Supply Si9711CY VCC 0.02 mF +3.3 VIN (Si9706DY: Pin 2, 3) (Si9707DY: Pin 3, 4, 5, 6) PC Card slot supply voltage. For the Si9706DY, connect pins 2 and 3 of the IC to pins 17 and 51 of the PC card connector. For the Si9707DY, pins 5 and 6 connect to slot A and pins 3 and 4 connect to the slot B pins 17 and 51. SR FIGURE 8. Si9711CY Sleep Mode (Si9706DY: Pin 8) (Si9707DY: Pin 9, 16) Connect a capacitor to the SR pin to adjust the slew rate of the VCC ramp. Recommended capacitance value is identified in the data sheet. GND ADVANCED SLEEP MODE SUPPORT Today's portable systems have multiple levels of suspend, sleep, or deep-sleep. In certain host platforms, a suspend mode may require maintaining an active slot with the +5-V supply turned off. The best application example for this case is a host platform with a fax/modem card that wakes the system on detecting a ring on the line. This kind of sleep can be done either by using an external circuit similar to the one shown in Figure 8 for suspending +12-V, or by reducing the +5 VIN to 3.3-V. The Si9712DY is functional with no increased on-resistance for card currents below 100 mA (Figure 10). 180 160 Supply Current ( m A) 140 120 100 80 60 (Si9706DY: Pin 1) (Si9707DY: Pin 8, 1) Ground reference connection. Connect this pin to host platform system ground. Suspend Power 5.5 V to 30 V 4 MAX783 VCCA Si9707DY ON5 SYNC SHDN VCCB Dual PC Card Slots Low-Battery Warning +3.3 V VPP Control ON3 Power Section +5 V S mP S Memory S Peripherals VPPA (0 V/5 V/12 V) VPPB (0 V/5 V/12 V) FIGURE 7. Power System Block Diagram Using MAX783 and Si9707DY for Dual PC Card Slots 40 20 SLEEP MODE SUPPORT One of the most common ways of extending battery life is to turn off those supplies which are not being used. Designs that support a power management philosophy that causes +12-V to be intermittent would find the Si9712DY a more suitable part. www.vishay.com S FaxBack 408-970-5600 0 3.0 3.5 4.0 4.5 +5 VIN - Supply Voltage (V) FIGURE 9. Si9712DY Current Draw During Suspend Document Number: 70587 14-Nov-97 6 AN716 Vishay Siliconix Si9711CY +12 V From System Supply +5 V +3.3 V CL 6710 SLOT_VCC VPP_PGM VPP_VCC -VCC_5 -VCC_3 VL S1 S2 S3 S4 33 mF +5 VIN +3.3 VIN PC Card Slot +12 VIN VPP 3.3 mF 18 52 VCC 33 mF 17 51 GND FIGURE 10.Si9711CY System Implementation Si9712DY +12 V From System Supply +5 V +3.3 V CL 6710 A_VPP_PGM A_VPP_VCC A_VCC_3 A_VCC_5 S1 S2 S3 S4 SR GND 33 nF VCC 33 mF 17 51 +12 VIN +5 VIN +3.3 VIN PC Card Slot A VPP 3.3 mF 18 52 Si9712DY +12 VIN +5 VIN +3.3 VIN B_VPP_PGM B_VPP_VCC B_VCC_3 B_VCC_5 S1 S2 S3 S4 GND VCC 33 mF SR 33 nF 17 51 VPP 3.3 mF 18 52 PC Card Slot B FIGURE 11.Si9712DY System Implementation Document Number: 70587 14-Nov-97 www.vishay.com S FaxBack 408-970-5600 7 AN716 Vishay Siliconix CONTROLLER INTERFACE WITH THE SI9711CY The Si9711CY has individual lines for each switch in the power interface. These control lines can be connected directly to industry-standard controllers that have active high outputs for the switch enables. For controllers that output active low signals for VCC control, such as the Cirrus 6710, the interface would require two inverting buffers as shown in Figure 11. The system power supply, or input side of the switch for 3.3-, 5-, and 12-V should have sufficient bypass capacitance to prohibit switching noise from feeding back into the system supply. For example, the bypass capacitor on +12 Vin has been selected as 10 X the bypass on the VPP output pin. Bypass capacitance on the 3.3-V and 5-V inputs will vary based on system implementation and the intended power level that the slot is intended to support. Capacitor values for VCC and VPP are left up to the individual system designer. However VCC should be at least 10 X the capacitance of VPP . They should be selected for optimum ESD protection since these pins interface directly to the PC Card slot. CONTROLLER INTERFACE WITH THE SI9712DY The Si9712DY interface supports both active-high and active-low VCC control. The smart switching feature allows the designer to swap the 3.3- and 5-V control to produce an active low interface as shown in Figure 11 with the Cirrus 6720 in a dual-slot configuration. CONTROLLER INTERFACE WITH THE SI9706DY/07DY The Si9706DY and Si9707DY interfaces directly to industry-standard PC Card controllers. The Si9707DY would provide the best system choice with the MAX783 dc/dc controller and the Cirrus 6720 dual slot PC Card controller. The Si9706DY and Cirrus 6710 with the MAX783 provide a complete solution for single slot configurations. The Si9706DY and Si9707DY support active high and active low control signals in the same way as Si9712DY. www.vishay.com S FaxBack 408-970-5600 8 Document Number: 70587 14-Nov-97 |
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