MIC2596A/2697A Micrel MIC2596A/2697A Dual Channel Negative Voltage Hot Swap Controllers Advance Information General Description Features The MIC2596A and MIC2597A are dual channel negative voltage hot swap controllers designed to facilitate safe PC board insertion into and removal from live backplanes. To minimize external components, each channel of the MIC2596A/MIC2597A has an integrated high voltage power MOSFET. Built-in current sensing in each channel provides inrush current limiting, by regulating the channel's output current to a user-settable maximum. Current sensing also provides programmable overcurrent and open-load detection. A channel will be turned off if it experiences overload or no-load conditions lasting longer than programmable intervals. Foldback current limiting holds power dissipation of the internal MOSFETs at safe levels during overloads, and very fast shutdown response to faults ensures protection for both system power supplies and the load. The MIC2596A will automatically attempt to restart into an overcurrent fault until the fault is cleared, while the MIC2597A will latch the output in the off state until it is reset by external action. A logiccompatible signal is provided on each channel to indicate overcurrent or undercurrent fault conditions. * * * * * * * * * Allows safe hot-swap in -48V systems Operates to -70V Programmable inrush current limiting Two thermally isolated channels Overcurrent fault sensing and protection Nuisance trip prevention circuitry Open-load detection Logic compatible Enable and Fault signals Separate analog and logic ground pins support large system ground differentials (8V) Applications * Central Office Switching * -48V Power Distribution Typical Application CL 6 VDDA 5 +3.3V RPU VCLAMP OUT1 19 ILIMIT 2 CGATE1 17 RPU VOUT1 VCC 20 FAULT#_CH1 11 FAULT#_CH2 CONTROLLER 1 ON/OFF_CH1 ON/OFF_CH2 FAULT#1 FAULT#2 CL ON1 10 ON2 15 VDDL C1 R1 MIC2596A GND 3 8 4 C2 OUT2 CTIMER1 12 CGATE2 14 ILIMIT2 9 VOUT2 CTIMER2 COL1 C4 C3 C5 COL2 VEE 7 R2 16 C6 VIN -48V System-Controlled Hot Swap Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com December 2000 1 MIC2596A/2697A MIC2596A/2697A Micrel Ordering Information MIC2596A/2697A Part Number ON Signal Circuit Breaker Function Package MIC2596A-1BTS Active-High Auto-Retry 20 pin TSSOP MIC2596A-2BTS Active-Low Auto-Retry 20 pin TSSOP MIC2597A-1BTS Active-High Latched Off 20 pin TSSOP MIC2597A-2BTS Active-Low Latched Off 20 pin TSSOP MIC2596A-1TSE Active-High Auto-Retry 20 pin Exposed Pad MIC2596A-2TSE Active-Low Auto-Retry 20 pin Exposed Pad MIC2597A-1TSE Active-High Latched Off 20 pin Exposed Pad MIC2597A-2TSE Active-Low Latched Off 20 pin Exposed Pad 2 December 2000 MIC2596A/2697A Micrel Pin Configuration ON1 1 20 FAULT#1 ILIMIT1 2 19 OUT1 CTIMER1 3 18 N/C COL1 4 17 CGATE1 VCLAMP 5 16 VEE VDD/VDDA* 6 15 VDDL* COL2 7 14 CGATE2 CTIMER2 8 13 N/C ILIMIT2 9 12 OUT2 ON2 10 11 FAULT#2 20-Pin TSSOP Pin Descriptions Pin Number Pin Name 20, 11 FAULT1#/FAULT2# 1, 10 ON1/ON2 Enable Input - Active-high (MIC259xA-1) or active-low (MIC259xA-2). When asserted ON will initiate a start cycle by activating the GATE output. Toggling ONx will also reset the circuit breaker in the MIC2597A. 3, 8 CTIMER1/CTIMER2 Current Limit Response Timer. A capacitor connected to this pin defines the period of time tFLT in which an overcurrent event must last to signal a fault condition and turn the output off. 16 VEE 2, 9 ILIMIT1/ILIMIT2 19, 12 OUT1/OUT2 6 VDDA 5 VCLAMP FAULT# Clamp Voltage. A small bias current into this pin (usually supplied by the controlling logic's supply voltage) powers internal circuitry which establishes the active low voltage of the FAULT# signals. In normal circuit configurations, the low-level output voltage will be clamped to VDDL. 4, 7 COL1/COL2 Open-Load Detect Timer - When the load current falls below 8% of full scale current limit the capacitor connected to COL1/COL2 begins to change. When the voltage across COL1/COL2 rises above 1.32V the output is immediately shut off. When ONx is deasserted or when the load current is above 15% of full scale current limit then this pin is held to VEE. Tying this pin to VEE will disable this function. 17,14 CGATE1/CGATE2 15 VDDL 13, 18 N/C December 2000 Pin Function Fault Status Output, Active-low - Asserted when the circuit breaker trips upon overcurrent, open-load or thermal shutdown conditions. Negative Supply Voltage Input. Current Limit Set. The current limit threshold is set by connecting a resistor between this pin and VEE. When the current limit threshold of a channel is exceeded for tFLT the circuit breaker for that channel is tripped and its respective output is immediately shut off. Switch Outputs. Connect to load. Positive Supply Input. Normally connected as the power ground reference in negative supply (-48V) systems. VDDA is the IC's "analog ground," used for internal biasing relative to -VEE. Noise filtering capacitors for the gates of the main output MOSFETs. Typically in the range of 1000pF ~ 4700pF. VDDL provides the ground reference for the logic-compatible FAULT# and ON signals, while accommodating 8 volts of ground differential between the controlling logic and the power ground (VDDA) of the MIC2596A/2597A. If no differential voltage capability is required between VDDA and VDDL, these two pins should be tied together at the part. No Connect. 3 MIC2596A/2697A MIC2596A/2697A Micrel Absolute Maximum Ratings Operating Ratings (All voltages are referred to VEE) (Note 1) Supply Voltage (VDDA to VEE) ........................ -0.3V to 80V Supply Voltage (VDDA to VEE) ........................ -0.3V to 80V VCLAMP pin (Note 2) ...................................... -0.3V to 5.5V ON, FAULT# pins (Note 2) ............................ -0.3V to 5.5V Junction Temperature .............................. Internally Limited ESD (Human Body Model) ........................................... [tbd] ESD (Machine Model) .................................................. [tbd] Supply Voltage (VDDA to VEE) ........................... 15V to 70V Supply Voltage (VDDL to VEE) ........................... 15V to 70V VCLAMP (relative to VDDL) .............................. 2.5V to 5.25V Ambient Temperature ................................ -40C to +85C TSSOP Package: .......................................... JA = 90C/W TSE Exposed Pad Package (Note 3) ............ JA = 38C/W Continuous Junction Temperature ........... 125C Maximum Electrical Characteristics VDDA = VDDL = 40V, VEE = 0V, VCLAMP = VDD + 3.3V, RLIMIT1 = RLIMIT2 = 20k , TA = 25C unless otherwise noted. Symbol Parameter Condition Min IDD Supply Current VDDA = VDDL = 70V, Both outputs on or off -40C to 85C UVLO Undervoltage Lockout threshold VIN rising Undervoltage Lockout hysteresis VIN falling ICLAMP CLAMP pin supply current FAULT#1 and FAULT#2 are high VCLAMP = 5.25V VOL FAULT#[1/2] output low voltage (Note 2) IOL = 250A RDSON On-Resistance (Each Switch) Typ Max Units 3.3 5.0 mA 12.5 V 11.5 V 190 A -0.18 0.4 V TJ = 25C 1.5 2.0 On-Resistance (Each Switch) TJ = 85C 1.9 2.5 CLF Current Limit Factor (Notes 4, 6) RLIMIT1 = RLIMIT2 = 40k 2000 2300 A* IOFF Off-state Output leakage current Switch is off, TJ = 25C VOUT = VDDA = VDDL = 70V 2 A Off-state Output leakage current Switch is off, TJ = 85C VOUT = VDDA = VDDL = 70V 5 A ITIMER IOLDTH -0.3 -0.35 1700 Overcurrent Timer pull-down current 1.1 1.9 2.7 A Overcurrent Timer charge current -42 -72 -103 A Open Load Detect threshold IOUT decreasing 6 9 12 % (percent of full-scale output current) (Notes 5, 6) IOUT increasing 8 12 16 % IOLDHYS Open Load Detect hysteresis (percent of full-scale output current) VTHHI Overload Timer Capacitor high-going threshold voltage 1.12 1.32 1.52 V VTHLO Overload Timer low -going threshold voltage for auto-restart (MIC2596A) (Note 6) 0.21 0.24 0.27 V IGATE CGATE Capacitor charge current VCOL Open Load Detect Timer high-going threshold voltage 1.12 1.32 1.52 V ICOL Open-Load Detect Timer capacitor charge current -10 -17 -24 A VFBU Output voltage foldback threshold Upper threshold 25 31 37 V Lower threshold 10 13 16 V VOUT - VEE > VFBU, % of full scale current limit 12 20 28 % VFBL IFOLDBACK Foldback output current limit MIC2596A/2697A 3 During turn-on 4 % A -79 December 2000 MIC2596A/2697A Micrel Symbol Parameter Condition VIL ON Pin Low threshold Voltage IIL Min Typ Max Units -40C to 85C 0.8 V ON Pin input current VON = VCLAMP 150 A VIH ON Pin High threshold voltage -40C to 85C TPROTECT Thermal self-protection points TJ increasing (turn-off) 145 C TJ decreasing (turn-on) 135 C 2.0 V AC Parameters tON Turn-on time CL = 1F, RL = 1k, CGATE = 1nF [tbd] ms tOFF Turn-off time CL = 1F, RL = 1k, CGATE = 1nF [tbd] ms tR Rise-time CL = 1F, RL = 1k, CGATE = 1nF [tbd] ms tF Fall-time CL = 1F, RL = 1k, CGATE = 1nF [tbd] ms tOC Current limit response time CGATE 1nF 4 s tOFF(UVLO) Undervoltage to OUT1/OUT2 off response time CL = 1F, RL = 1k, CGATE = 1nF [tbd] s Notes: Note 1: Absolute Maximum Ratings are those ratings beyond which a part may be permanently damaged. Functionality is not guaranteed when a part is operated at its Absolute Maximum Ratings. Note 2: Relative to VDDL. Note 3: The exposed pad of the TSE package must be connected to VEE of the part, or be electrically isolated. Note 4: The current limit threshold is defined by the current limit factor divided by RLIMIT, the resistor connected to the ILIMIT1/ILIMIT2 pins. Note 5: Open Load Detect is not guaranteed to function for programmed maximum output currents <[tbd]mA Note 6: Final production value TBD. Timing Diagrams Device Under Test VOUT OUT tF tR RL CL 90% VOUT 10% ON/OFF ON/OFF 50% tOFF tON VOUT 50% tOFF 90% VOUT 10% MIC2596A-1 MIC2597A-1 December 2000 10% tON 90% 90% 10% MIC2596A-2 MIC2597A-2 5 MIC2596A/2697A MIC2596A/2697A Micrel Functional Diagram CONTROLLER GROUND SYSTEM CONTROLLER VDDL Rpullup1 Rpullup2 VDDA MIC2696A MIC2597A VCLAMP ON1/ON2 3.3V or 5V Supply Control Signals Status Signals VOUT1 VOUT2 FAULT#1/FAULT#2 VEE Figure 1. Use of VDDA and VDDL to Mitigate Ground Noise Effects Functional Description Hot Swap Insertion When circuit boards are inserted into systems with live power supplies, high inrush currents can result due to the charging of bulk capacitance that resides across the circuit board's supply pins. This inrush current, although transient in nature, can be of significant amplitude. Such current spikes can cause supply voltages to go out of regulation, resulting in system crashes. Additionally, the high rates of di/dt may do permanent damage to electronic components and/or assemblies. The MIC2596A family of parts is designed to address these issues by limiting the inrush current which a PC board or other load can draw during a hot-swap event. In addition to this inrush current control, the MIC2596A/MIC2597A provide output current limiting and supervisory functions to ensure robust protection for both the host system and the circuit board. VDDA and VDDL In some systems, considerable ground differentials can occur between the physical plant monitor and the actual power control circuitry. An example of this would be in a system spanning several racks of equipment, with a centralized CPU watching over the hot-swap functions. In order to alleviate the need for optical isolators or similar devices when hot-swap parts are used in such a system, the MIC2596A/MIC2597A have separate grounds for their on-chip power-related functions and their digital interface pins (ON1, ON2, FAULT1#, FAULT2#). The unique architecture of these parts allows voltage differentials of 8 volts to exist between VDDA (the MIC2596A/2697A "analog" ground) and VDDL (the "logic" ground), without disturbing device performance. In distributed systems, VDDA should be connected to the local return of the power which the MIC2596A/MIC2597A is controlling, while VDDL should be separately connected to the monitor and control logic's ground. See Figure 1. If the capability to tolerate voltage differentials between VDDA and VDDL is not required, the two grounds should be tied together at the chip. Start-Up Cycle Referring to the Typical Applications Circuit, when a channel's ON pin is asserted the respective MIC2596A/MIC2597A output is enabled. To minimize inrush current transients the output current is regulated to ensure that it does not exceed the value programmed by the resistor R1(R2) connected to the ILIMIT pin. Circuit Breaker Function The MIC2596A and MIC2597A act as electronic circuit breakers to protect loads, connectors, power supplies, and other system components against faults such as short circuits. The circuit breaker function trips upon overcurrent, open-load or thermal shutdown conditions. The FAULT# output is asserted (taken low) when the circuit breaker is tripped. The timer capacitor C2 (C3) is normally pulled low by a small current source. However, whenever the current limit threshold is exceeded C2 is charged by a much stronger current source. If an overcurrent condition exists for a long enough time to allow the voltage at the CTIMER pin to cross the 6 December 2000 MIC2596A/2697A Micrel threshold VTHHI , the circuit beaker is tripped and the output is immediately turned off. This time-out period tFLT prevents the circuit breaker from erroneously tripping due to inrush currents during start-up or other transient currents caused by normal system operation. The MIC2596A circuit breaker has an automatic-reset function. After the circuit breaker trips a new start-up cycle is initiated. If the fault still exists C2 (C3) will again charge up to VTHHI and trip the circuit breaker. C2 will then be discharged, and when the voltage across C2 goes below VTHLO another start cycle is initiated. This will continue until the fault is removed or the channel is turned off. In the MIC2597A the circuit breaker is only reset by either toggling the ON pin or cycling input power. The MIC2597A will be enabled to start up only if the voltage across CTIMER is below VTHLO. Foldback Current Limiting During short circuits or excessive loads the MIC2596A and MIC2597A employ foldback current limiting. When the differential from VEE to VOUT reaches -13V, the output current starts to fold back. When (VEE - VOUT) reaches -31V, the output current will be limited to approximately 20% of its full scale value. Figure 2 illustrates the foldback function. 100% IOUT (%of ILIM) 20% 13V 31V VOUT - VEE Figure 2. Foldback Characteristics Fault Status Indication The MIC2596A and MIC2597A will assert the FAULT# output whenever their circuit breaker function is activated by an overcurrent condition. A fault will also be indicated if an openload or thermal shutdown condition is detected. Figure 3 shows FAULT# timing scenarios. t > tFLT t < tFLT ILIMIT ILOAD IOLDTH t > tFLTOL FAULT# ON (MIC2597A-1) Figure 3. MIC2597A Fault Timing December 2000 7 MIC2596A/2697A MIC2596A/2697A Micrel resistance is RLIMIT(NOMINAL) = (1A*2000)/ILIMIT. As an example, if the maximum DC current from one channel of an MIC2596A was to be 0.15A, the nominal value of RLIMIT for that channel would be (1A* 2000)/0.15A = 13.3k. It is usually necessary, however, to allow for device tolerances: using a 13.3k resistor and the minimum Data Sheet value Current Limit Factor of (1A*1700)/RLIMIT could restrict the part to delivering only 127mA. Therefore, it is necessary to use RLIMIT = (1A*1700)/ILIMIT to find RLIMIT's minimum value: 1700/0.15A = 11.3k. This revised value should then be tested against the other extreme of the IC's Data Sheet tolerance. 11.3k could program a steady-state DC current as high as (1A*2300)/11.3k = 203mA maximum. The system must be designed to accommodate this maximum current, or RLIMIT can be made adjustable over the range necessary to maintain a precise 150mA DC current limit (11.3k - 15.3k). In order to minimize error budget issues, the use of a 1% tolerance resistor for RLIMIT is generally recommended. CTIMER A capacitor from CTIMER to VEE sets the length of time for which an overcurrent fault is allowed to exist on a channel before the channel goes into shutdown. CTIMER is normally pulled down to VEE by a small current (1.9A nominal). During an overcurrent condition, the pulldown current is replaced by a charging current of 72A nominal. The output will be disabled once the voltage on CTIMER becomes 1.32V greater than VEE. Given these numbers, it's easy to program the time an MIC2597A will tolerate an output overload before "tripping" and shutting its output off, using the formula CTIMER = (72A*TOL/1.32V). For example, if it's desired to allow 50msec for the load capacitance to charge up before the MIC2597A declares a "fault," then CTIMER = (72A*50msec/ 1.32V) = 2.7F. For the MIC2596A, there is a slight modification to the above formula, due to the MIC2596A's auto-retry feature. When an overcurrent condition occurs, CTIMER will (as with the MIC2597A) charge at a 72A rate towards 1.32V. Once that threshold is reached, the output will be turned off. However, instead of being latched off as with the MIC2597A, it will turn on again when the voltage across CTIMER is discharged back to 0.24V by the 1.9A internal pulldown. The first fault timeout period following power-on will therefore be TOL = (CTIMER*1.32V/72A), but the following retry intervals will be of duration T OL = [C TIMER *(1.3V-0.24V)/72A] = (CTIMER*1.06V/72A). Rearranging, we get: CTIMER = (72A*TOL /1.06V). Again using 50msec as an example for the desired fault timeout, this gives C TIMER = (72A*50msec/1.06V) = 3.4F. In this case, 3.3F would be a good choice for CTIMER. The maximum voltage to which CTIMER will charge is less than 2V, so a 4.7V voltage rating on the capacitor provides ample safety margin. Note that, for the MIC2596A, the ratio of CTIMER charge and discharge currents are always 38:1. This means that in an overload fault condition, the part will attempt to restart the load with a duty cycle of approximately 2.5%, which is low Application Information Thermal Shutdown and Power Dissipation Thermal shutdown protection is employed to protect the internal power MOSFETs from damage. Whenever the junction temperature TJ of the channel in current limit exceeds 145C the output is immediately shut off without affecting the other channel. A channel will automatically turn on again when its TJ falls below 135C. The junction temperature is related to the internal power dissipation of the MIC2596A (MIC2597A). The equation for junction temperature is: TJ = [(JA * PD) + TA] where: TJ is the junction temperature, PD is the total power dissipation of the part, and TA is the ambient temperature. PD is determined by adding the power dissipated by each MOSFET to the power dissipated by the internal circuitry (PCHIP). The equation for PD is thus: PD = PCHIP + PFET1 + PFET2 = (VEE x IEE) + [(I12) x RDS(ON)1] + [(I22) x RDS(ON)2] where I1 and I2 are the continuous output currents of channels 1 and 2. For example, to compute the maximum continuous output current per channel of the TSSOP package at VEE = -48V, TA = 70C, and TJ(CONTINUOUS) = 125C: R(J-A) = 90C/W PD(MAX) = (125C - 70C)/(90C/W) = 0.611W 0.611W = (-48V x -5mA) + (2 x IMAX2 x 2.5) 0.371W = 2 x 2.5 x IMAX2 0.371W/(2 x 2.5) = IMAX2 = 0.0742 A2 IMAX = 272mA per channel Similarly, for the TSE package, at T A = 85C and TJ(CONTINUOUS) = 125C: R(J-A) = 38C/W PD(MAX) = (125C - 85C)/(38C/W) = 1.05W 1.05 W = (-48V x -5mA) + (2 x IMAX2 x 2.5) 0.81W = 2 x 2.5 x IMAX2 0.81W/(2 x 2.5) = IMAX2 = 0.162 A2 IMAX = 402mA per channel Note that in each case the assumption has been made that the load currents will be the same on both channels. External Components A small number of passive components are used for each channel of the MIC2596A/MIC2597A to program such values as maximum DC output current and the short circuit "trip" interval. Calculating values for these parts is a straightforward exercise, once the nomenclature for and effect of each such part is understood. This section addresses each programmable pin by showing a sample calculation for that pin. RLIMIT A resistor from ILIMIT to VEE sets the maximum DC operating current of the channel. The formula for calculating this MIC2596A/2697A 8 December 2000 MIC2596A/2697A Micrel enough to protect the IC and the system, yet high enough to prevent undue restart delays. COL One of the special functions of the MIC2596A family of parts is the ability to detect not only overload faults, but also undercurrent (open-load) faults. The time for which a channel's output must see a load below a minimum current level (which is a preset percentage of ILIMIT - see the Data Sheet Electrical Tables) is set by COL. When an undercurrent condition is detected, COL is charged from 0V relative to VEE towards a threshold voltage of 1.32V above VEE by a current of 17A (nominal). This gives the formula COL = (17A*TOL/1.32V). For example, if a no-load detection period of 75msec is desired, COL is found to be 0.97F. 1F is the closest standard value. Once the output current goes above the minimum load current, COL is discharged to VEE. The maximum voltage to which COL will charge is less than 2V, so a 4.7V voltage rating on the capacitor provides ample safety margin. It is important to note that neither the MIC2596A nor the MIC2597A will attempt an "auto-retry" upon detecting an open-load condition. If either of these parts shuts one or both of its output off following such a condition, the affected output(s) can only be turned on again by turning the channel(s) off and then back on, or by cycling the power to the IC. If the open load detection capability is not needed for a given channel, it can be defeated by tying the COL pin for that channel to VEE. CGATE This pin is a direct connection to the gate of each channel's internal power MOSFET. Typically, it is used to connect a capacitor in the range of 1000pF to 4700pF between the MOSFET gate and VEE, to augment the noise immunity of the channel. This especially helps with regard to dv/dt appearing on the channel's output, which could otherwise couple through the drain-gate capacitance to the MOSFET's input. As the internal MOSFET is an N-channel device in the negative leg of the channel's power path, the negative terminal of CGATE should connect to VEE, and its positive terminal to the IC's CGATE pin. A voltage rating of 15V is well suited to the approximately 10V which will appear on CGATE when the internal MOSFET is fully enhanced. CL 6 VDDA 5 N/C 20 N/C 11 1 ILIMIT 2 CGATE1 17 VOUT1 CL ON1 15 VDDL 4 19 FAULT#2 ON2 8 OUT1 FAULT#1 10 3 C2 VCLAMP C1 R1 MIC2596A-2 OUT2 CTIMER1 12 CGATE2 14 ILIMIT2 9 VOUT2 CTIMER2 COL1 C4 C3 COL2 7 VEE R2 16 VIN -48V Stand Alone Hot Swap Application December 2000 9 MIC2596A/2697A MIC2596A/2697A Micrel Package Information 5.40 (0.213) 5.20 (0.205) 7.90 (0.311) 7.65 (0.301) DIMENSIONS: MM (INCH) 0.875 (0.034) REF 7.33 (0.289) 7.07 (0.278) 2.00 (0.079) 1.73 (0.068) 0.38 (0.015) 0.25 (0.010) 0.21 (0.008) 0.05 (0.002) 0.65 (0.0260) COPLANARITY: BSC 0.10 (0.004) MAX 10 4 0.22 (0.009) 0.13 (0.005) 1.25 (0.049) REF 0 -8 0.95 (0.037) 0.55 (0.022) 20-Pin SOP (TS) 5.40 (0.213) 5.20 (0.205) 7.90 (0.311) 7.65 (0.301) DIMENSIONS: MM (INCH) 0.875 (0.034) REF 7.33 (0.289) 7.07 (0.278) 2.00 (0.079) 1.73 (0.068) 0.38 (0.015) 0.25 (0.010) 0.21 (0.008) 0.05 (0.002) 0.65 (0.0260) COPLANARITY: BSC 0.10 (0.004) MAX 10 4 0 -8 0.22 (0.009) 0.13 (0.005) 1.25 (0.049) REF 0.95 (0.037) 0.55 (0.022) Exposed Pad Bottom View 20-Pin Exposed Pad SOP (TS) MICREL INC. TEL 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. (c) 2000 Micrel Incorporated MIC2596A/2697A 10 December 2000