AP-211 CALIFORNIA MICRO DEVICES Instantly Available PCI Card Power Management Introduction Today, PCs need to remain constantly connected to the outside world, but at the same time consume minimum power. Even when looking idle, it is still possible to receive a message from the Internet or an incoming fax or phone call. The PC must automatically go from sleep mode to on mode; in other words, an Instantly Available PC (IAPC). The challenge is to maintain a systems modem or Local Area Network (LAN) connectivity on a desktop PC/workstation while at the same time minimizing power consumption. These power management features are called Wake-on-Ring (or Wakeon-Modem), Wake-on-LAN, and Wake-on-PME (Power Management Event). The main qualities/benefits of such a system are: Listening: available anytime to receive messages from the outside world, and Reacting: responding anytime to do a specific operation (maintenance ), and Saving energy and being silent in the idle mode. The OnNow initiative by Microsoft defined the new requirements for the system that affect both software and hardware aspects of the PC: Windows operating system, applications, device drivers, and hardware within the system. All these elements must work together in order to provide a fully transparent power management system. This note will focus only on the hardware aspects. ACPI System Design An instantly available PC appears to be off, yet it can snap back to its full ready state within seconds and respond to the phone ringing in time to service the call. In order to meet these requirements a recommendation, the Advanced Configuration and Power Interface specification (ACPI), has been defined by Intel, Microsoft, and Toshiba. Instantly available motherboards include: ACPI BIOS, ACPI chip set, and PCI slots that are compliant to the PCI-PM specification. The Intel chip set supports the power management features to define the ACPI sleep states and also generates the signals to control power planes to turn the main power supplies on and off. The implementation includes multiple power sources and uses separate power planes in the system. Each power source is selected depending on the required state demanded by the system, and one of the major requirements is to switch between power sources continuously, automatically, and without interruption. The sleep state of an instantly available PC is called Suspend to RAM. This is implemented by using: split power planes in the system design, and an auxiliary power source (VAUX) for dual mode power distribution. Lets focus on the PCI (Peripheral Component Interface) cards, where California Micro Devices products have their primary applications. By definition, all PCI add-on cards are connected to the motherboard through the PCI bus. On the PCI connector, several pins have been reserved in order to support the instantly available functionality. PME# (Power Management Event) pin (pin #A19) is used to wake the system in response to a PCI power management wake event such as the phone ringing. 3.3Vaux pin (pin #A14) is used to deliver the auxiliary power of 3.3V to all the wake-up PCI cards in the system. This power is always available to keep the card active even when the rest of the PCI bus is without power. Three different independent voltage sources are now available on the PCI bus: 3.3VAUX, 3.3VCC, and 5VCC. In a power plane partitioning system of an instantly available PC, the 3.3VAUX is electrically isolated from the main PCI 3.3V rail at all times. During normal operation, the 3.3VAUX supply remains on all the time, while the other main supplies, 3.3VCC and 5VCC, can be switched on and off as needed. PCI Adapter Card Application PCI Network Interface Cards (NIC) and modem cards are also designed with split power planes. Thus, they are able to operate in sleep mode with only the Vaux power supply and still be able to wake-up the system. Some NICs that operate in Wake on LAN mode get a 5V standby through a cable that connects directly to a specific header on the motherboard. Chip Set Voltage Today, PCI card chip sets or ASICs operate at a low voltage of 3.3V. That allows much lower power consumption than with the previous 5V modem chips. However older PCs are still operating at 5V and do not have any 3.3VAUX supply. New PCI cards must be compatible with these systems still in service, and therefore must regulate on board their own 3.3V supply from the 5V. This is made possible by using California Micro Devices SmartOR power management products: the CMPWR100 and CMPWR150. In addition, there is a maximum current limitation of 375mA on the 3.3VAUX. All trademarks are the property of their respective holders. ©1999 California Micro Devices Corp. All rights reserved. P/Active® is a registered trademark and SmartOR is a trademark of California Micro Devices. 9/99 215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 C0210699A Fax: (408) 263-7846 www.calmicro.com 1 AP-211 CALIFORNIA MICRO DEVICES Power Requirements on VAUX In order to limit the power consumed by the system in the sleep mode, each PCI card must reduce its current consumption from the auxiliary power supply. The power operating conditions are displayed below. Param e te r D e scription P o we r e d b y d u a l 3 . 3 V AU X MIN TY P MAX UN I T 3.0 3.3 3.6 Volts 375 mA 20 mA All these parts are general purpose smart voltage regulators and/or switches. They can be used in PCI modem, PCI LAN card, or dual power system applications. Figures 1-3 below illustrate a simplified block diagram of each of the power management devices. . p o we r c i r c u i t I ma x _ e n a b l e d Sleep state wake up I ma x _ d i s a b l e d Sleep state wake up enabled d i sa b l e d Table 1. Power Requirements for VAUX That means that each PCI add-in cards load on 3.3VAUX must not exceed 375mA. When the board is in a sleep state with wake up event generation disabled, it must reduce its total slot current to less than 20mA which can be done several ways: . internally disabling as much logic as possible on the board, or electrically isolating the 3.3VAUX pin from the auxiliary electrically isolating the 3.3V pin from the auxiliary power plane of the board. AUX power plane of the board. . Figure 1. CM PWR-100 Block Diagram VCC Dual Power Supply A dual mode power supply is able to deliver the same reference voltage from two separate tuned (load-wise) power sources. For example, a main power source will provide a high capacity, high efficiency 3.3V source for heavy runtime loads, and a lower capacity auxiliary source, yet reasonably efficient, 3.3V source for lightly loaded sleeping states. A voltage switch is required in order to select between one of these two different sources. This can be implemented with discrete Schottky diodes, or more efficiently, with California Micro Devices power switch, the CMPWR025. VOUT DRIVE GND Figure 2. CM PWR-150 Block Diagram California Micro Devices has developed a family of SmartORTM Power Management devices to address all these requirements whose characteristics are summarized in Table 2 and will be the primary focus of this application note. VCC1 D e v ic e F u n c t io n CMP W R 1 0 0 R e g u l a to r a n d V IN V OUT I OUT [V] [V] [ m A] 4.5 to 5.5 3.3 < 200 8-pin SOIC < 500 5-pin TO-263 t o V OU T Regulator VOUT or S wi t c h f r o m V AU X CMP W R 1 5 0 Pack age VAUX 4.5 to 5.5 3.3 or VCC2 8-pin SOIC GND VAUX CMP W R 0 2 5 Dual Input Switch 2.8 to 5.5 VCC1 < 500 or 8-pin SOIC 8-pin MSOP VCC2 Table 2. Summary of Power Management Devices 2 215 Topaz Street, Milpitas, California 95035 Figure 3. CMPWR025 Block Diagram In the next sections, we will discuss specific applications for the CMPWR100 and CMPWR150. In order to facilitate the design process, California Micro Devices has available a SmartORTM evaluation board for use in the lab and to facilitate PCB layout. Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com 9/99 AP-211 CALIFORNIA MICRO DEVICES Hysteresis Hysteresis is illustrated in Figure 4 and is defined as the difference between the enabling threshold (when the regulator turns on) and the disabling threshold (when the regulator turns off). The hysteresis level sets up the maximum level of acceptable noise or disturbance on V CC or V AUX. This is particularly critical during power transitions. In order to avoid disturbance and given the hysteresis of the devices, the recommended maximum total resistance is shown in Table 3. VCC [V] VCC transient V Transient CC Hyste re sis I m ax R e sistance D e vice [mV ] [mA] [W] CMP W R 1 0 0 150 200 0.75 CMP W R 1 5 0 250 500 0.5 CMP W R 0 2 5 50 or 100 500 0.1 or 0.2 Table 3. Recommended maximum series resistances during turn off to prevent chatter Enable threshold The worst case condition occurs during turn on, when there is in-rush current. During turn on, the current is rising from 0A to a high in-rush current. The in-rush current level and duration is increased when the initial output capacitor voltage is 0V, and when the capacitor value is larger. We can assume an in-rush current equal to twice the maximum DC load current of the device. Table 4 below gives a recommendation for the maximum series resistances during turn on. Hysteresis Disable threshold time [usec] Figure 4. Input voltage transient and hysteresis D e vice As shown in Figure 5, the voltage seen by the device is given by: Vcc_in = Vcc (Rs X I) - (Rt X I) (Lt X dI/dt) CMP W R 1 0 0 where, Vcc is the power supply voltage, Rs is the power supply output impedance, Rt is the interconnect series resistance (between supply and regulator), and Lt is the trace (line) inductance (between supply and regulator). Hyste re sis I n-rush I m ax R e sistance [mV ] [mA] [W] 150 400 0.375 CMP W R 1 5 0 250 1000 0.25 CMP W R 0 2 5 50 or 100 1000 0.05 or 0.1 Table 4. Recommended maximum series resistances during turn on to prevent chatter Although a filter capacitor at the input can reduce the effective source impedance for short transients, long in-rush current durations may still cause chatter. Power supply CMPWR100 POWER MANAGEMENT APPLICATION CM PWR-150 Rs Rt Lt output + Vcc Vcc_in C RL Figure 5. Equivalent circuit with line parasitic Figure 5. Equivalent circuit with line parasitic Assuming an ideal situation where there is no parasitic inductance, the hysteresis level should follow the equation below. Vhysteresis > (Rs X I) + (Rt X I) Where Rs is the power supply output impedance and Rt is the interconnect series resistance (between supply and regulator). 9/99 215 Topaz Street, Milpitas, California 95035 Device Operation The CMPWR100 is a power management device able to generate a continuous 3.3V at 200mA from two voltage sources: a 5V main supply (VCC) or a 3.3V auxiliary supply (VAUX). The device integrates a low dropout voltage regulator, an integrated low impedance switch, and control circuitry to switch from the VCC to VAUX supply. When the 5V is present, the device automatically enables the regulator that produces 3.3V output at VOUT. When only the 3.3V is present, the device provides a direct connection from the VAUX pin to the VOUT pin with a very low impedance of 0.2Ω typically. This will minimize power consumption when in sleep mode. The worst case is when a maximum current of 200mA is flowing which results in a power dissipation (loss) across the switch of only 8mW. Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com 3 AP-211 CALIFORNIA MICRO DEVICES The CMPWR100 gives priority to the primary input VCC over the secondary input VAUX. It also provides an internal reference voltage at 4.1V used to set the threshold. When the primary VCC drops below this threshold, VAUX becomes the selected input source. To prevent chatter, the threshold logic has a built-in hysteresis of 150mV, and the primary source is only selected again when the VCC level exceeds 4.25V typically. All control circuitry needed to provide a smooth and automatic transition between supplies has been incorporated, allowing the VCC to be dynamically switched without loss of output voltage. A STATUS output pin is used to indicate an acceptable VCC level. Internal circuitry guarantees that high isolation is maintained between both supplies under all operating conditions. Typical Applications 1 5V main To PCI bus + 0.1µF 4.7µF 2 Vcc Status Vaux Vout1 7 Vaux 0.1µF 4 + 6 3 3.3V Vaux 8 Gnd Vout2 nc 0.1µF As stated earlier, the STATUS pin may be used to indicate the state of the regulator. It is active High when the regulator is turned on (VCC> VTHRES), and may be used to drive the gate of an external P-channel MOSFET switch in parallel with the integrated PMOS switch for Vaux. This will provide an even lower ON resistance between Vaux and Vout, thus lowering power dissipation further. To be efficient, the external switch should have an on-resistance of less than 400mΩ at VGS = 3V and ID =0.2A. CMPWR150 POWER REGULATOR APPLICATION Device Operation The CMPWR150 employs a circuit topology similar to the CMPWR100, but utilizes an external P-channel MOSFET to switch Vaux at current levels up to 375mA. The CMPWR150 is designed to regulate up to 500mA of continuous output current when operating from VCC. The external switch handles all the VAUX requirements. The CMPWR150 exceeds the PCIdefined maximum 375mA load capability. 3.3V output 4.7µF 5 CM PWR-100 Figure 6. Dual Input Power Management Circuit All control circuitry needed to provide a smooth and automatic transition between supplies has been incorporated. This offers trouble-free transitions between input voltages, or between sleep and wake-up modes. Internal circuitry guarantees that high isolation is maintained between the VCC supply and the output under all operating conditions. The VCC to VAUX isolation is achieved by disabling the external PFET when the regulator is enabled. The VOUT to VCC isolation is achieved by forcing the regulator pass transistor to be disabled. In a PCI modem application, regulator is used to provide backward compatibility for 3.3V modems with older systems where only 5V is provided on the PCI bus. The CMPWR100 is used to generate the 3.3V on board from a 5V source. The two Vaux input pins must be connected together to the 3.3Vaux provided on new systems. The VCC input is compared to a 4.1V internal threshold level. Whenever VCC drops below that level, the regulator is disabled and the DRIVE output is enabled (active low). The DRIVE output is used to control an external P-channel MOSFET switch for connecting an auxiliary 3.3V voltage source to the load. When the regulator is enabled, the DRIVE output is set to VCC. In order to maintain regulator stability and minimize disturbance on power supplies during change over between input sources, an external 4.7µF capacitor is required between the output and ground. The external capacitor provides the necessary filtering to minimize transients during supply change over and ensures regulator stability. Most Tantalum type capacitors are recommended. But the capacitor should have a low ESR (Equivalent Series Resistance). The value of the capacitor may be increased to minimize switch over transients. 1. The P-channel MOSFET must have a low on resistance at low voltage: 1. The P-channel MOSFET must have a low on resistance X IDmax) > Voutmin VAUX (RDS(ON) at low voltage: A bypass capacitor in the range of 1µF to 10µF may be connected between VCC and ground in order to filter out voltage transients. This is recommended for longer PCB trace connections between the input and the power supply, inducing large series resistance. 4 215 Topaz Street, Milpitas, California 95035 Typically, (on)X must be Vless than 200mΩ at VGS = 3V VAUX RDS (RDS(ON) IDmax) > OUTmin and ID = 375mA. A typical 75mV voltage across switch at is V applicable Typically, RDS(ON) mustdrop be less thanthe 200mΩ = 3V GS for most cases. and ID = 375mA. A typical 75mV voltage drop across the switch is applicable 2. The must typically have a gate threshold voltage for MOSFET most cases. of 1V. We The recommend Siliconix Si2301DS, FDN338P, or 2. MOSFET must typically have a Fairchild gate threshold voltage equivalent. of 1V. We recommend the Vishay Siliconix Si2301DS, Fairchild FDN338P, or equivalent. Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com 9/99 AP-211 CALIFORNIA MICRO DEVICES Typical Applications 3.3V. In this case, the device will go into current limiting until VOUT goes back to its nominal level. A large Tantalum capacitor of 10µF or greater is recommended. P-channel MOSFET 3.3V Vaux To PCI bus nc Drive 2 5V main Vcc + 0.1µF 10µF 3 Output Capacitor 5 1 Vout Gnd 4 + 0.1µF 3.3V output 10µF CM PWR-150 During power transitions, a previously charged capacitor will provide the current to the load until the regulator or the auxiliary supply take over. A larger Tantalum capacitor at the output will improve this transition, and a value of 10µF or greater is recommended. High Frequency Capacitors Figure 7. Power Regulator Circuit Cold-Start Behavior A cold-start situation occurs when a PC is powered ON. Typically, power supplies take milliseconds to reach their nominal voltage. Both the 5V and 3.3V voltage sources are ramping up together. As soon as the 5V source reaches the regulator_enable 4.25V threshold, the regulator turns ON. At that time the output capacitor begins to rapidly charge and pulls a large transient current which can easily exceed values of 1 ampere. It is, therefore, very important to take into consideration the parasitic series resistances and parasitic inductance between the supply voltage Vcc and the device. The voltage seen by the device is given by: Additionally ceramic chip capacitors can be placed next to both inputs and output pins to reduce the high frequency noise. A value of 0.1µF is recommended. Supply Transient Characteristics A resistive load of 6.8Ω is used, setting a load current of 485mA at 3.3V. VCC power-up 0V to 5V (cold-start) with VAUX open circuit VCCIN = VCC - (RS x I) - (Rt x I) - (Lt x dI / dt) where, Vcc is the power supply voltage, Rs is the power supply output impedance, Rt is the interconnect series resistance (between supply and the CMPWR150), and Lt is the trace (line) inductance (between supply and the CMPWR150). Clearly a large, rapidly changing current will create a significant change in Vcc in, and if the input level drops below the regulator_disable 4.1V threshold, the regulator will turn OFF. The input level will then start to rise back toward 5V, turning the regulator back ON. This results in an unstable state (motor boating) where the regulator turns on and off until the output capacitor is finally charged to the 3.3V level. Input Capacitor To minimize the unstable state effect, an input capacitor is required in close proximity to the VCC input pin. When a transition occurs from VAUX to VCC, the capacitor is used as a charge reservoir to provide current to the load as well. This is especially critical when the output capacitor is not yet charged at power-up, or when the output level is much lower than 9/99 215 Topaz Street, Milpitas, California 95035 Figure 8 Ch1: VCC, offset 4.1V Ch2: VOUT Ch3: DRIVE Figure 8 shows VCC approaching the enable threshold during a 0V to 5V initial power-up transition (or cold-start). VAUX is left open. When VCC reaches the 4.3V enable threshold, the regulator turns ON. The large in-rush current caused by the uncharged output capacitor generates a voltage drop of about 230mV on the VCC pin. The 250mV hysteresis ensures the regulator remains enabled during the transient. Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com 5 AP-211 CALIFORNIA MICRO DEVICES VCC power-up with VAUX=3.3V Ch1: VCC, offset 4.1V Ch2: VOUT, offset 3.3V Ch3: DRIVE VCC power-down with VAUX=3.0V Ch1: VCC, offset 4.1V Ch2: VOUT, offset 3.3V Ch3: DRIVE Figure 9 Figure 9 shows VCC approaching the enable threshold during a 0V to 5V transition. VAUX is set to 3.3V DC. In this case, the output capacitor is already set to 3.3V, so that when the regulator turns ON, the in-rush current is minimized. The transition on VOUT is clean. The test set-up series resistance on the VCC input is estimated at about 160mΩ. At full load, the output voltage is above 3.2V. Figure 11 Figures 11 - 14 show power-up and power-down transitions with VAUX set to 3.0V and 3.6V. VCC power-down with – VAUX=3.6V VCC power-down with VAUX=3.3V Ch1: VCC, offset 4.1V Ch2: VOUT, offset 3.3V Ch3: DRIVE Figure 12 VCC power-up with VAUX=3.0V Ch1: VCC, offset 4.0V Ch2: VOUT, offset 3.3V Ch3: DRIVE Figure 10 Figure 10 shows VCC approaching the disable threshold during a 5V to 0V transition. VAUX is set to 3.3V DC. When VCC goes down to the 4.1V disable threshold, the regulator turns OFF. The rebound on VCC is due to the step change of the voltage drop across the series resistance of the input. The output voltage VOUT experiences a negative glitch due to the parasitic resistance and inductance on the VAUX line. The 250mV hysteresis ensures the regulator remains enabled during the transient. 6 215 Topaz Street, Milpitas, California 95035 Ch1: VCC, offset 4.1V Ch2: VOUT, offset 3.3V Ch3: DRIVE Tel: (408) 263-3214 Figure 13 Fax: (408) 263-7846 www.calmicro.com 9/99 AP-211 CALIFORNIA MICRO DEVICES VCC power-up with – VAUX=3.6V The board interfaces to the following signals: Input power supply voltages VCC, VSBY, VAUX, and GND. Output voltage and signal: VOUT and STATUS (or DRIVE). It provides pad layouts for mounting two decoupling chip capacitors for each input and output of the device, as well as for a SOT-23 external P-channel MOSFET switch for the CMPWR150. Ch1: VCC, offset 4.1V Ch2: VOUT, offset 3.3V Ch3: DRIVE Heat spreaders are provided on the printed circuit board to improve the power dissipation for the regulator devices (i.e. CMPWR100). These are used when the devices operate under a high current load or heating condition. Various sizes of heat spreaders are provided with a copper area of up to 2 inch2. Figure 14 Conclusion Instantly Available PCs require unique Power Management devices to provide regulated voltage sources and smart switches between power sources. California Micro Devices provides high performance integrated solutions to reduce component count and ease the design and manufacturing cycles. California Micro Devices SmartORTM products allow interface card manufacturers to meet the power requirements of IAPC. To find a solution to your specific requirement, call California Micro Devices for applications assistance. VCC power-up from 0V to 5V (cold-start) with VAUX open Bad test set-up with total series resistance of 0.7Ω on VCC, by using an additional resistor of 0.5Ω. References [1] CMPWR100 data sheet, 200mA Dual Input Power Management Circuit, Rev. 9/99, California Micro Devices. [2] CMPWR150 data sheet, 500mA / 3.3V SmartORTM Power Regulator, Rev. 9/99, California Micro Devices. [3] CMPWR025 data sheet, 500mA Dual Input SmartORTM Power Switch, Rev. 9/99, California Micro Devices. Ch1: VCC, offset 4.1V Ch2: VOUT Ch3: DRIVE [4] Instantly Available Power Managed Desktop PC, Design Guide, Rev. 1.2, 9/25/98, Intel Corp. Figure 15 Figure 15 shows a cold-start power-up transition for a test set-up with a total series resistance of 0.7 Ω on VCC. This is described in the cold-start behavior paragraph. Evaluation Board The SmartORTM evaluation board is intended to facilitate the use of California Micro Devices Power Management device family, and will accommodate any individual device with installation one at a time on the board. For example, operating the CMPWR100 requires populating that device and the external capacitors around it. To obtain a board, simply contact your local California Micro Devices Sales Representative or call the Factory direct at 1-(800) 325-4966 and ask to be connected to Applications. 9/99 215 Topaz Street, Milpitas, California 95035 [5] Instantly Available PC, System Power Delivery Requirements and Recommendations, Rev. 1.0, 12/30/97, Intel Corp. [6] PCI Bus Power Management Interface Specification Rev. 1.1, 12/18/98, PCI Special Interest Group. Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com 7