Z-one Digital Iba Open Power Architecture Including Micrel Mic68200 Low Dropout Regulators

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Z-OneTM Digital IBA MIC68200 Z-OneTM Digital IBA Open Power Architecture Including Micrel MIC68200 Low Dropout Regulators APPLICATION NOTE REV. 1.0 AUG 21, 2006 Page 1 of 23 Z-OneTM Digital IBA MIC68200 TABLE OF CONTENTS INTRODUCTION ........................................................................................................................................................ 3 1. REFERENCE DOCUMENTS....................................................................................................................... 3 2. MIC68200 DESCRIPTION ........................................................................................................................... 3 3. TEST SETUP DESCRIPTION ..................................................................................................................... 3 4. APPLICATION EXAMPLES ........................................................................................................................ 5 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 Tracking................................................................................................................................................... 5 Monitoring ............................................................................................................................................... 6 Sequencing ............................................................................................................................................. 7 Fault Propagation ................................................................................................................................... 9 Cascading.............................................................................................................................................. 11 Closed Loop Tracking.......................................................................................................................... 13 Ratiometric Tracking............................................................................................................................ 14 Tracking Bus Terminator ..................................................................................................................... 15 System Power-On Reset Signal .......................................................................................................... 19 Interrupts ........................................................................................................................................... 21 CONCLUSIONS ....................................................................................................................................................... 23 CONTACT INFORMATION...................................................................................................................................... 23 REV. 1.0 AUG 21, 2006 Page 2 of 23 Z-OneTM Digital IBA MIC68200 Introduction This document describes an open architecture system comprised of ZM7300 digital power manager (DPM), ZY7000 point of load (POL) converters, and Micrel MIC68200 adjustable low dropout (LDO) regulators. The architecture cost-effectively addresses power conversion and power management needs of both low and high current outputs. 1. Reference Documents ZY7XXX Data Sheet ZM7300 Data Sheet ZM7300 Programming Manual MIC68200 Data Sheet 2. MIC68200 Description The MIC68200 is a low dropout (LDO) regulator designed specifically to drive demanding digital circuits such as FPGAs, PLDs, DSPs, and microcontrollers. The MIC68200 incorporates a ramp control pin (RC) for tracking applications and output voltage rising slew rate adjustment. In addition, there is a delay pin (DLY) for control of power-on-reset output (POR) at turn-on and turn-off. The MIC68200 can implement a variety of power-up and power-down schemes such as sequencing, tracking, and ratiometric tracking. The MIC68200 operates from a wide input range of 1.65V to 5.5V. It is fully protected offering both thermal and current limit protection and reverse current protection. The MIC68200 has a junction temperature range of –40°C to +125°C and is offered in the tiny 10-pin 3mm x 3mm MLF package. Refer to the MIC68200 data sheet available on www.micrel.com for more detailed information. 3. Test Setup Description The testing was performed using the system consisting of a ZM7300 DPM, two ZY7115 POL converters, and a MIC68200YML LDO regulator. The block-diagram of the system is shown in Figure 1. Note, that some components and connections, such as decoupling capacitors, etc. that are not relevant to the subject of the application note were omitted for clarity. Figure 1. Block-Diagram Of The Open Architecture System REV. 1.0 AUG 21, 2006 Page 3 of 23 Z-OneTM Digital IBA MIC68200 In all tests the intermediate bus voltage was 5.0V and the DPM was powered from a 3.3V source. The output voltage of a MIC68200 was programmed with the resistors R1 and R2 calculated from the equation: ⎛ R1 ⎞ VOUT = 0.5 × ⎜ + 1⎟ , ⎝ R2 ⎠ (1) where VOUT is the desired output voltage in Volts. The ZM7300 Digital Power Managers have a number of digital outputs and inputs intended for control of devices other than Z-OneTM POL converters. In the test system, the DPM’s output EN0 was used to control the MIC68200 and the input PG0 was used to monitor its POR output. A specific configuration file was developed to control the test system. The GUI System Configuration Window with the configuration file is shown in Figure 2. Figure 2. GUI System Configuration Window REV. 1.0 AUG 21, 2006 Page 4 of 23 Z-OneTM Digital IBA MIC68200 Z-OneTM POL converters were located at addresses 01 and 02. The output with the address 03 was assigned to control and monitoring of the MIC68200. For the purposes of programming and monitoring, the GUI treats the LDO regulator as an “auxiliary device”. 4. 4.1 Application Examples Tracking The MIC68200 has the ramp control (RC) pin which can be used to control the voltage at the output. When the voltage on the RC pin is below 0.5V, the RC pin controls the output voltage. When it is at or above 0.5V, the output is controlled by the LDO’s internal regulator. If a capacitor is connected to the RC pin, the bidirectional current source will charge the capacitor during turn-on and discharge the capacitor during turn-off. The size of the capacitor and the RC pin current (1µA nominal) control the rising slew rate of the output voltage according to the equation below: dV ⎛ 1µA = 2 × VOUT × ⎜⎜ dt ⎝ C RC ⎞ ⎟ , V/ms ⎟ ⎠ (2) Where CRC is the value of the ramp control capacitor in nF. In the block-diagram in Figure 3, the MIC68200 is controlled by the DPM via the EN0 output connected to its EN pin and monitored via the PG0 pin connected to its POR output. Since both EN0 and PG0 pins are internally pulled up to 3.3V no external interface components are required. The slew rate of the output voltage of the MIC68200 is set with the capacitor connected to the RC pin. The value of the capacitor is selected to match the rising slew rate of the Z-OneTM POL converters. Figure 3. Tracking Configuration A tracking turn-on process is illustrated by Figure 4. REV. 1.0 AUG 21, 2006 Page 5 of 23 Z-OneTM Digital IBA MIC68200 Figure 4. Tracking Turn-On. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 The slew rates of Z-OneTM POL converters and turn-on delays for both Z-OneTM POL converters and MIC68200 are determined by the configuration settings programmed via the Z-OneTM Graphical User Interface and stored in the DPM. In Figure 4 the turn-on delays were set to zero so all outputs started rising simultaneously. 4.2 Monitoring The GUI is continuously monitoring and reporting status of the MIC68200 via its PG0 pin connected to the POR pin of the MIC 68200. The status of the MIC68200 is displayed in the GUI Monitoring window shown in Figure 5 in the Aux Devices box. In addition, the status can be read directly from DPM status registers via the industrystandard I2C communication bus. Refer to ZM7300 Programming Manual for more information. If the MIC68200 is enabled, operating properly, and its POR signal is high, the Power Good square will turn to green. Note, that a DPM starts monitoring status of the POR signal only after it enables the LDO regulator via the EN0 pin. REV. 1.0 AUG 21, 2006 Page 6 of 23 Z-OneTM Digital IBA MIC68200 Figure 5. GUI Monitoring Window 4.3 Sequencing By programming different turn-on delays via the Graphical User Interface it is very easy to realize various sequencing schemes. The GUI Sequencing/Tracking window is shown in Figure 6 and different sequencing arrangements are illustrated by Figure 7-Figure 9. REV. 1.0 AUG 21, 2006 Page 7 of 23 Z-OneTM Digital IBA MIC68200 Figure 6. GUI Sequencing/Tracking Window Figure 7. Sequenced Turn-On. MIC68200 Has 10ms Turn-On Delay. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 REV. 1.0 AUG 21, 2006 Page 8 of 23 Z-OneTM Digital IBA MIC68200 TM Figure 8. Sequenced Turn-On. Z-One POL Converters Have 10ms Turn-On Delay. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 TM Figure 9. Sequenced Turn-On. MIC68200 Has 10ms Delay, Z-One POL Converters Have 0ms and 20ms Turn-On Delay. Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 4.4 Fault Propagation It is also possible to include the MIC68200 in the overall protection scheme by enabling the fault propagation from Z-OneTM POL converters to the LDO regulator. The propagation is enabled by checking appropriate boxes in the GUI Fault Management and Fault Propagation windows shown in Figure 10 and Figure 11. REV. 1.0 AUG 21, 2006 Page 9 of 23 Z-OneTM Digital IBA MIC68200 Figure 10. GUI Aux Device Fault Management Window Figure 11. GUI Fault and Error Propagation Window When the propagation is enabled, any fault in a Z-OneTM POL converter will pull the EN0 pin of the DPM low disabling the MIC68200. In Figure 12, a Z-OneTM POL converter shuts down because of an undervoltage on its output. As soon as the undervoltage condition is detected, the turn-off signal is generated. It disables both the Z-OneTM POL converter and the MIC68200 so each device shuts down according to their turn-off delay settings. Since the Z-OneTM POL converter is programmed to auto-restart, both devices attempt to restart every 130ms until the condition causing the undervoltage is removed. In the test, turn-off delay was set to 0ms for MIC68200 and to 25ms for the Z-OneTM POL converter. REV. 1.0 AUG 21, 2006 Page 10 of 23 Z-OneTM Digital IBA MIC68200 Figure 12. Fault Propagation In Case Of Undervoltage Fault Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 4.5 Cascading If it is necessary to delay the turn-on of a MIC68200 until the outputs of Z-OneTM POL converters reach regulation, the EN pin of the MIC68200 can be connected to the Power Good outputs of the Z-OneTM POL converters as shown in Figure 13. Figure 13. Cascading Configuration In this case, the output of the MIC68200 starts ramping up as soon as Power Good outputs of both Z-OneTM POL converters are released. The PGOOD pins are internally pulled up to 3.3V so no additional interface components REV. 1.0 AUG 21, 2006 Page 11 of 23 Z-OneTM Digital IBA MIC68200 are required. Performance of the system is illustrated by Figure 14. Figure 14. Cascading. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 There are two drawbacks of setting the slew rate with an external capacitor. First, it is an open loop tracking scheme. While it is possible to achieve close slew rate matching by selecting the value of the capacitor, there is no guarantee the tracking will be maintained under all application conditions over life of the product. If the RC capacitor changes over time, the rising slew rate of a MIC68200 will change accordingly, potentially violating tracking requirements. Second, the falling slew rate of a MIC68200 is not a specified parameter. It is much higher than its rising slew rate determined from (2) so tracking during turn-off cannot be realized as shown in Figure 15. Figure 15. Turn-Off Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 REV. 1.0 AUG 21, 2006 Page 12 of 23 Z-OneTM Digital IBA 4.6 MIC68200 Closed Loop Tracking A more reliable way to implement tracking between a MIC68200 and Z-OneTM POL converters is shown in Figure 16. Figure 16. Closed Loop Tracking Configuration In this configuration, the output voltage of the MIC68200 is controlled by the output voltage of a Z-OneTM POL converter. The voltage is fed into the RC pin via the resistive divider R3/R4. In essence, it is a Master/Slave configuration where the output voltage of the slave (MIC68200) always follows the output voltage of the master (ZOneTM POL converter). Since the slew rate of the master POL converter is programmed by the user via the GUI, then the slew rate of the MIC68200 is effectively programmed via the GUI. By changing the R3/R4 divider ratio it is possible to set the slew rate of a MIC68200 to be a multiple of the slew rate of the master POL. Assuming that K is the ratio of the slew rate of a MIC68200 to the slew rate of the ZOneTM POL converter driving its RC pin, it can be shown that: R 3 1 ⎛ R1 ⎞ = ×⎜ + 1⎟ − 1 , R 4 K ⎝ R2 ⎠ (3) Where R1 and R2 are determined from the equation (1). Therefore, to achieve accurate tracking K must equal 1, or the divider R3/R4 should have the same ratio as the voltage-setting divider R1/R2 as long as the output voltage of the master is greater than the output voltage of the slave. If the voltages are equal, the ratio of the divider should be adjusted to track approximately 50mV higher than the voltage of the master. The pictures in Figure 17 and Figure 18 were taken with R3=33k and R4=11k. configuration, the tracking is now accomplished during both turn-on and turn-off. REV. 1.0 AUG 21, 2006 Unlike in the previous Page 13 of 23 Z-OneTM Digital IBA MIC68200 Figure 17. Closed-Loop Tracking Turn-On. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 Figure 18. Closed-Loop Tracking Turn-Off. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 4.7 Ratiometric Tracking For K=2 (the output voltage of the MIC68200 rises and falls twice as fast as the output of the Z-OneTM POL converter), R3 was changed to 11k. The pictures in Figure 19 and Figure 20 show performance of the system with ratiometric tracking. REV. 1.0 AUG 21, 2006 Page 14 of 23 Z-OneTM Digital IBA MIC68200 Figure 19. Closed-Loop Ratiometric Tracking Turn-On. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 Figure 20. Closed-Loop Ratiometric Tracking Turn-Off. TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 4.8 Tracking Bus Terminator A more practical application of the ratiometric tracking is an active bus terminator. In applications including memory buses, it is frequently required to generate the termination voltage equal to 50% of the reference voltage to optimize performance of memory buses. Such condition corresponds to K=½ in the equation (3). In the block diagram in Figure 21, the Z-OneTM POL converter generates 1.5V to power memory banks (Vddq). The voltage is also used as a reference voltage to drive the RC pin of the MIC68200 and the ratio of the divider is selected so the REV. 1.0 AUG 21, 2006 Page 15 of 23 Z-OneTM Digital IBA MIC68200 output voltage of the linear regulator (Vtt) is equal to ½ of the output voltage of the Z-OneTM POL converter from zero to 1.5V. Figure 21. Tracking Bus Terminator Configuration Note that in active memory bus termination applications the LDO regulator will have to both source and sink the output current. Refer to the MIC68200 data sheet for sink current specifications. Performance of the tracking bus terminator is illustrated by Figure 22-Figure 24. Figure 22. Tracking Bus Terminator Turn-On. Ch1 – Vddq, Ch3 – Vtt REV. 1.0 AUG 21, 2006 Page 16 of 23 Z-OneTM Digital IBA MIC68200 Figure 23. Tracking Bus Terminator Turn-Off. Ch1 – Vddq, Ch3 – Vtt Figure 24. Bus Terminator Output Voltage Tracking. Ch1 – Vddq, Ch3 – Vtt Not only the MIC68200 tracks the output of the Z-OneTM POL converter during normal conditions as shown in the pictures above, it also tracks the output during fault conditions as shown in Figure 25 and Figure 26. REV. 1.0 AUG 21, 2006 Page 17 of 23 Z-OneTM Digital IBA MIC68200 Figure 25. Undervoltage Fault. Ch1 – Vddq, Ch3 – Vtt In Figure 25 the Vddq shuts down because of an undervoltage. Z-OneTM POL converters consider the undervoltage fault to be non-critical so the output shuts down according to pre-programmed turn- off slew rate and delay. It restarts automatically every 130ms until the condition causing the undervoltage is removed. As it can be seen in the picture, Vtt is always 50% of Vddq during the shutdown and restart processes. Figure 26. Overcurrent Fault. Ch1 – Vddq, Ch3 – Vtt In case of an overcurrent or short circuit on the output of Vddq, the output shuts down as soon as the current reaches its overcurrent protection threshold as shown in Figure 26. Vtt continues tracking Vddq during the REV. 1.0 AUG 21, 2006 Page 18 of 23 Z-OneTM Digital IBA MIC68200 shutdown and recovery when the condition causing the overcurrent is removed. 4.9 System Power-On Reset Signal The block-diagram in Figure 27 shows a way to generate a Power-On Reset (POR) signal representing status of all power supplies in the system, both Z-OneTM POL converters and MIC68200 LDO regulators. Figure 27. System Power-On Reset Signal In this configuration, the Power Good outputs of Z-OneTM POL converters are connected directly to the POR output of the MIC68200. The PGOOD pins are internally pulled up to 3.3V so no additional interface components are required. When all power supplies are in regulation, the POR and PGOOD pins will be released, pulling the system POR line high as shown in Figure 28. If the line is connected to a monitoring input of the DPM as shown by the dashed line, the user will be able to observe the system POR status in the IBS Monitoring window or read it directly from status registers via the I2C bus. Refer to ZM300 Data Sheet and Programming Manual for more details. REV. 1.0 AUG 21, 2006 Page 19 of 23 Z-OneTM Digital IBA MIC68200 Figure 28. System POR Signal At Turn-On POL Converters, Ch3 – MIC68200, Ch4 – System POR Line TM Ch1, Ch2 – Z-One Ch1, Ch2 – Z-One Figure 29 System POR Signal At Turn-Off POL Converters, Ch3 – MIC68200, Ch4 – System POR Line TM The capacitor CDLY can be connected between the DLY pin of a MIC68200 and the ground to program the time delay between all power supplies reaching regulation and the release of the system POR line. The delay may be required to guarantee that the power has been stable for a certain period of time before resetting microprocessors and other logic devices. The delay programmed by the capacitor is calculated from the equation: REV. 1.0 AUG 21, 2006 Page 20 of 23 Z-OneTM Digital IBA MIC68200 DELAYPOR = 1.1× C DLY 1µA (4) Where DELAYPOR is in ms, if CDLY is in nF. Therefore, an addition of a 10nF capacitor to the DLY pin of a MIC68200 programs the POR delay of approximately 10ms as shown in Figure 30. Figure 30. System POR Signal At Turn-On With Time Delay TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200, Ch4 – System POR Line Note, that in the given configuration, there is no POR delay at the turn-off regardless of the value of the CDLY. The POR signal is always pulled low as soon as the outputs of Z-OneTM POL converters start ramping down as shown in Figure 29. 4.10 Interrupts More complex system configurations can be realized by using advanced features of both Z-OneTM Digital IBA and MIC68200 LDO regulators. The configuration shown in Figure 31 allows programming of slew rates, turn-on, and turn-off delays independently for Z-OneTM POL converters and MIC68200 LDO regulators. In addition, it realizes cascading and status monitoring. REV. 1.0 AUG 21, 2006 Page 21 of 23 Z-OneTM Digital IBA MIC68200 Figure 31. Sequencing/Cascading/Tracking Configuration The rising slew rate of the MIC68200 is programmed with the CRC; however the turn-on delay is determined by the DPM (programmed by the user via the GUI). Once the MIC68200 reaches regulation, it will release the POR signal after the delay programmed by the CDLY. The POR signal will, in turn, release the interrupt input of the DPM that was held low during the power-up process. Since the interrupt is programmed to control the Z-OneTM POL converters as shown in the GUI Interrupt Configuration window in Figure 32, they will start ramping up according to their turn-on delay and rising slew rate settings. The turn-on process for such configuration is shown in Figure 33. In the test all turn-on delays were set to zero. Figure 32. Interrupt Configuration Window REV. 1.0 AUG 21, 2006 Page 22 of 23 Z-OneTM Digital IBA MIC68200 By using the interrupt input of the DPM and the POR output of the MIC68200, the configuration ensures that ZOneTM POL converters turn-on only after the output voltage of the LDO regulator has reached regulation and been established for a certain period of time. The delay time between the two events is programmed by CDLY or via the GUI. In case of a failure on the output, the MIC68200 will turn-off the Z-OneTM POL converters via the INT0_N pin. Figure 33. Turn On Via Interrupt TM Ch1, Ch2 – Z-One POL Converters, Ch3 – MIC68200 Conclusions The MIC68200 low dropout linear regulators integrate seamlessly into Z-OneTM Digital Power Architecture facilitating power management features such as sequencing, cascading, tracking, active bus termination, and monitoring. The open architecture described above addresses power and management needs for the wide range of applications – from milliamps to hundreds of amps. Contact Information Power-One Inc. 740 Calle Plano, Camarillo, CA 93012 USA Tel +1 (805) 987-8741 http:/www.power-one.com Micrel, Inc. 2180 Fortune Drive, San Jose, CA 95131 USA Tel +1 (408) 944-0800 Fax +1 (408) 474-1000 http:/www.micrel.com 2 I C is a trademark of Philips Corporation. REV. 1.0 AUG 21, 2006 Page 23 of 23