LX1676 I N T E G R A T E D P R O D U C T S Mobile AMD Athlon VRM Controller P RELIMINARY D ATA S HEET KEY FEATURES DESCRIPTION maximizing regulator response. A true differential input amplifier is used for remote voltage sensing at the processor core. A VID code generator provides an internal reference that will set the output voltage. This VID code can be changed during operation and the reference will slew the output voltage to its new setting at a preset rate. During VID changes on the fly the Power Good indication will stay valid. Current through the lower phase 1 MOSFET will be sampled using its RDS(ON) for current limit and shut down. For further protection, an over voltage circuit will trip at a specified setting and clamp the output by turning off the upper MOSFETs and turning on the lower MOSFETs. The upper MOSFET drivers will use a bootstrap capacitor to provide the upper drive voltage over the input voltage range of 6 to 32 volts. IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com † Patent numbers US6292378,US6285571,US6356063 High Current Biphase Operation Outputs As Low As 0.925V † Biphase LoadSHARETM † Transient Correction Loop Reduces Required Capacitance Differential Amplifier For Remote Voltage Sensing Integrated High Current MOSFET Drivers 200KHz to 1MHz Frequency Operation Programmable Slew Rate Control For Start-Up Sequence and VID change VID Changes On The Fly Power Good Indicator Short Circuit Protection Output Over Voltage and Under Voltage Protection No current-sense resistors WWW . Microsemi .C OM The LX1676 is a highly integrated VRM power supply controller IC featuring two PWM switching regulator stages. The two constant frequency voltage-mode PWM phases are configured as a single biphase high current output core supply. In biphase operation, the high current (>25A) output is generated by a LoadSHARETM† technique that balances the currents in the two phases. Power loss and noise, due to the ESR of the input capacitors, are minimized by operating the PWMs 180° out of phase. A synchronized Transient Correction Loop† provides exceptional control of the output droop and overshoot during very high di/dt load changes, the circuit can be configured for droop only, overshoot only or both. This architecture also minimizes capacitor requirements while APPLICATIONS AMD Mobile Athlon or Duron Processor Core Voltage Supply Voltage Regulator Modules PRODUCT HIGHLIGHT T r a n s ie n t C o r r e c tio n L o o p V in + 5 V V in 6 to 3 2 V 100nH 5 B it V ID LX1676 V in 6 to 3 2 V Vout LX1676 PACKAGE ORDER INFO TJ (°C) 0 to 70 LQ Plastic MLPQ Plastic TSSOP PW 38-Pin 38-Pin LX1676-CLQ LX1676-CPW Note: Available in Tape & Reel. Append the letter “T” to the part number. (i.e. LX1676-CLMT) Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET 1 38 36 37 35 34 ILIM3 EA2LP2 LP1 ILIM1 FBDFOUT EO1 EA1DACOUT PWGD GND VIN ROSC ENA VID4 VID3 33 32 31 2 30 3 29 4 28 5 27 Connect Bottom to Power GND 6 7 26 25 8 24 9 23 10 22 11 12 21 13 14 15 16 17 18 WWW . Microsemi .C OM Supply Input Voltage (VCCL, VCC)............................................... -0.3V to 6.0V Battery Input Voltage (VIN) ............................................................. -0.3V to 36V Current Limit Sense (ILIM1, ILIM3) ............................................... -0.3V to 36V Topside Driver Supply Input Voltage (VC1, VC2, VC3) ............. -.3 toVSx 6.0V Topside Driver Return Input Voltage (VS1, VS2)............................... -5V to 36V Differential Sense Input Voltage (FB+, FB-)................................... -0.3V to 6.0V VID0 – VID4, Input Voltage .............................................................. -0.3V to 6V High Side Driver Peak (<500ns) Current (HO1/2, I-MAX)............................ +1A Low Side Driver Peak (<500ns) Sink Current (LO1/2, I-MIN) ................... +1.5A Operating Junction Temperature.................................................................. 150°C Storage Temperature Range...........................................................-65°C to 150°C Lead Temperature (Soldering 10 seconds)................................................... 300°C FB+ EO2 PACKAGE PIN OUT 19 20 VS3 I-MAX VC3 VC1 HO1 VS1 LO1 PGN LO2 VCCL I-MIN PGN3 VID2 VID1 VID0 VS2 HO2 VC2 VCC ABSOLUTE MAXIMUM RATINGS Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal. x denotes respective pin designator 1, 2, or 3 LQ PACKAGE (Top View) THERMAL DATA LQ Plastic MLPQ 38-Pin THERMAL RESISTANCE-JUNCTION TO CASE, θJC θJA 8°C/W 35°C/W θJC THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA ?°C/W ?°C/W THERMAL RESISTANCE-JUNCTION TO AMBIENT, PW Plastic TSSOP 38-Pin THERMAL RESISTANCE-JUNCTION TO CASE, Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. FBDFOUT EO1 EA1DACOUT PWGD GND VIN ROSC ENA VID4 VID3 VID2 VID1 VID0 VS2 H02 VC2 VCC 1 38 19 20 FB+ EO2 EA2LP2 LP1 ILIM1 ILIM3 VS3 I-MAX VC3 VC1 HO1 VS1 LO1 PGN LO2 VCCL I-MIN PGN3 PW PACKAGE (Top View) PACKAGE DATA Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET WWW . Microsemi .C OM FUNCTIONAL PIN DESCRIPTION Name Description FB+ Differential Amplifier Positive Input – Feedback from output FB- Differential Amplifier Negative Input – Feedback from output DFOUT EA1- Differential Amplifier Output Phase 1 Error Amplifier Negative Input EO1 Phase 1 Error Amplifier Output GND Analog Ground ROSC A resister to ground sets PWM frequency ENA Enable Input – Logic Low disables all converter phases DACOUT DAC Output voltage – 50uA bi-directional current source VID4 Digital Input for VID code – Has an internal pull-up resister VID3 Digital Input for VID code – Has an internal pull-up resister VID2 Digital Input for VID code – Has an internal pull-up resister VID1 Digital Input for VID code – Has an internal pull-up resister VID0 PWGD VCC VC3 Digital Input for VID code – Has an internal pull-up resister Power Good Output Pin – Open drain output pin for power good indication. High = Power Good IC Supply Voltage. Nominal +5V Supply for transient correction phase upper MOSFET driver, bootstrap voltage PGN3 Power ground pin for Transient Correction Loop driver I-MIN Output Driver for lower Transient Correction Loop MOSFET VS3 Low side of upper driver for Transient Correction Loop – MOSFET Driver power return I-MAX Output Driver for upper Transient Correction Loop MOSFET ILIM3 Transient Correction Loop current sense – A resister sets an upper limit for over current detection and shut down. Phase 2 differential amplifier positive input, filtered feedback from phase 1 output Negative Input of phase 2 integrating amplifier EO2 Output of phase 2 integrating amplifier LP2 Phase 2 differential amplifier negative input, filtered feedback from phase 2 output VIN Battery Voltage Input. LO2 Driver Output for phase 2 lower MOSFET VS2 Low side of upper gate driver for phase 2. HO2 Driver Output for phase 2 upper MOSFET VC2 Supply for phase 2 upper MOSFET driver, bootstrap voltage PGN Power ground pin for current sensing of lower MOSFET RDS(ON) for phase 1. LO1 ILIM1 Driver Output for phase 1 lower MOSFET Over-Current Limit Set – A resister sets an upper limit for over current detection and shut down. VS1 Low side of upper gate driver for phase #1. HO1 Driver Output for phase 1 upper MOSFET VC1 Supply for phase 1 upper MOSFET driver, bootstrap voltage VCCL PACKAGE DATA LP1 EA2- Voltage bus for the lower MOSFET drivers. Nominal +5V Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1676 I N T E G R A T E D P R O D U C T S Mobile AMD Athlon VRM Controller P RELIMINARY D ATA S HEET Parameter Symbol Min LX1676 Typ Max Units ` IC Input Supply Voltage Battery Input Voltage Biphase Topside Driver Return Voltage Transient Correction Phase Driver Return Voltage VCC VIN VS1, VS2 VS3 4.2 5.5 0 0 5.5 35 35 5 V V V V WWW . Microsemi .C OM RECOMMENDED OPERATING CONDITIONS ELECTRICALS Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET ELECTRICAL CHARACTERISTICS Parameter ` Symbol Low Side Driver Operating Current High Side Driver Operating Current Unity Gain Bandwidth Output Voltage Swing Unity Gain Bandwidth Slew Rate 9 1 mA µA ENA = VCC, FB+ = FBENA = GND IQ(VCCL) ENA = VCC, FB+ = FB- 0.5 1 mA IQ(VCx) ENA = VCC, FB+ = FB- 2 4 mA 6 100 mV nA dB V VOS IEA1 Common Mode Voltage (VCM) = 1.4V VICM CMRR > 50dB IEA1 = 2mA IEA1 = -20uA VOS ADA CMRRDA RIN VCM VDFOUT(MAX) VDFOUT (MIN) UGBW SR -6 -100 60 0.8 70 2.5 4.0 0.15 20 0.5 V MHz VCM=1.4V -6 0.99 0.8V < VCM < 2.5V Measured at FB+ Input 1 65 30 0 VDFOUT = 0V IDFOUT = 2mA IEA1 = -20uA 6 1.01 3 5 4.0 0.2 10 5 mV V/V dB kΩ V mA V MHz V/µs OSCILLATOR Maximum Clock Frequency Minimum Clock Frequency Frequency Stability fMAX fMIN RPWM=10kΩ RPWM=50kΩ 0.9 180 1 200 4 1.1 220 MHz KHz % PWM OUTPUT Maximum Duty Cycle DCMAX Minimum Pulse Width Dead Time tPWM(MIN) Ramp Amplitude VRAMP During Transient Correction Switching Transient Correction Not switching 3000pF Load 3000pF Load at 50% of VCCL VIN = 6V VIN = 12 VIN = 24 V 100 50 40 50 60 80 0.70 1.40 2.80 200 % Ns Ns V PHASE 2 INTEGRATING AMPLIFIER Input Offset Voltage DC Open Loop Gain Output Voltage Swing Unity Gain Bandwidth Copyright 2000 Rev. 0.3, 2002-12-30 VOS VEO2(MAX) VEO2(MIN) UGBW VCM=1.4V -6 IEA2 = 2mA IEA2 = -20uA Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 6 70 4.0 0.15 20 0.5 MV DB V MHz Page 5 ELECTRICALS ` 5 Units DIFFERENTIAL AMPLIFIER Input Offset Voltage Gain Common Mode Rejection Ratio Input Resistance Input Common Mode Range Source / Sink Current ` 1 Max IQ(VCC) VEO1(MAX) VEO1(MIN) UGBW Output Voltage Swing ` LX1676 Typ ERROR AMPLIFIER: PHASE 1 Input Offset Voltage Input Bias Current DC Open Loop Gain Input Common Mode Range ` Min REGULATOR IC Supply Current ` Test Conditions WWW . Microsemi .C OM Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 70°C except where otherwise noted and the following test conditions: VCC = 5V, VCCL = 5V, VIN = 12V, Switching Frequency = 500KHz. LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET Parameter ` VOS ADA CMRRDA RB UGBW Min LX1676 Typ Max Units LP1=LP2 -6 0.98 Common Mode Voltage = 0 to 2 V 1 60 180 4 6 1.02 mV V/V dB KΩ MHz TRANSIENT CONTROL LOOP Voltage Droop Sense Propagation Delay : FB+ and FB- to I-MAX Voltage Overshoot Sense Propagation Delay : FB+ and FB- to I-MIN Voltage Droop Sense Threshold Voltage Overshoot Sense Threshold ` Test Conditions PHASE 2 DIFFERENTIAL AMPLIFIER Input Offset Voltage Gain Common Mode Rejection Ratio Input Resistance Unity Gain Bandwidth ` Symbol WWW . Microsemi .C OM ELECTRICAL CHARACTERISTICS (CONT) Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 70°C except where otherwise noted and the following test conditions: VCC = 5V, VCCL = 5V, VIN = 12V, Switching Frequency = 500KHz. 50 ns 50 ns VDFOUT Rising 3000pF Load 40 mV VDFOUT Falling 3000pF Load 40 mV CL = 3000pF, VCx - VSx = 5V 50 50 ns OUTPUT DRIVERS Driver ` Rise Time Fall Time High Side Driver Voltage: [VHOx - VVSx] Drive High Drive Low Low Side Driver Voltage: [VLOx – VPGN] Drive High Drive Low tRISE tFALL High Side Driver Current IHOx Lower MOSFET Driver Current ILOx VLOx = 20mA, VCCL - VPGN = 5.0 V VLOx = -20mA, VCCL - VPGN = 5.0 V VCx - VSx = 5.0 V, Load = 3300pf at <500nSec VCCL - PGN = 5.0 V, Load = 3300pf at <500nSec 4.8 IILIM1 tCSD(ILIM1) 4.9 0.1 V 0.2 V 0.2 1 A 1.5 A 44 200 50 400 60 500 µA nS 40 200 50 400 60 500 µA nS ELECTRICALS IILIM3 tCSD(ILIM3) ENABLE INPUT / VOLTAGE IDENTIFICATION (VID) Logic Low Threshold Hysteresis Pullup Resistance ` 4.9 0.1 TRANSIENT CORRECTION LOOP OVER CURRENT PROTECTION Current Sense Bias Current Current Sense Delay ` 4.8 PHASE 1 OVER CURRENT PROTECTION Current Sense Bias Current Current Sense Delay ` VHOx = 20mA, VCx - VSx = 5.0 V VHOx = -20mA, VCx - VSx = 5.0 V 1.5 0.3 100 V V KΩ 0.5 V POWER GOOD Low Output Voltage Copyright 2000 Rev. 0.3, 2002-12-30 VPWGD IPWGD = -3mA Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET Parameter ` Symbol Test Conditions Min LX1676 Typ Max Units UVLO VCC Threshold Hysteresis VCC Rising Threshold Hysteresis VIN Rising 4.2 0.3 V VIN ` 5.5 0.3 WWW . Microsemi .C OM ELECTRICAL CHARACTERISTICS (CONT) Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 70°C except where otherwise noted and the following test conditions: VCC = 5V, VCCL = 5V, VIN = 12V, Switching Frequency = 500KHz. OVER VOLTAGE PROTECTION Over Voltage Threshold ` UNDER VOLTAGE PROTECTION Under Voltage Threshold ` DAC - 1 ≤ VDACOUT ≤1.4 0.925 ≤ VDACOUT < 1 Initial DACOUT Accuracy High Side Driver Current IHOx Lower MOSFET Driver Current ILOx 2.35 V 0.800 V 1 2 1.4 < VDACOUT ≤ 2 VCx - VSx = 5.0 V, Load = 3300pf at <500nSec VCCL - PGN = 5.0 V, Load = 3300pf at <500nSec VID Logic High Threshold VID Hysteresis 0.5 % 1 A 1.5 A 1.3 0.3 2 V V VOLTAGE IDENTIFICATION (VID) CODE Copyright 2000 Rev. 0.3, 2002-12-30 VOUT (V) 2.000 1.950 1.900 1.850 1.800 1.750 1.700 1.650 1.600 1.550 1.500 1.450 1.400 1.350 1.300 Shutdown VID[4:0] 10000 10001 10010 10011 10100 10101 10110 10111 11000 11001 11010 11011 11100 11101 11110 11111 VOUT (V) 1.275 1.250 1.225 1.200 1.175 1.150 1.125 1.100 1.075 1.050 1.025 1.000 0.975 0.950 0.925 Shutdown Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 ELECTRICALS VID[4:0] 00000 00001 00010 00011 00100 00101 00110 00111 01000 01001 01010 01011 01100 01101 01110 01111 Page 7 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET SIMPLIFIED BLOCK DIAGRAM VCCL EO1 EA1 4 WWW . Microsemi .C OM DFOUT 2 22 3 I-MAX 28 VC1 - 0° - 27 HO1 R - 26 VS1 + + FB - 1 + Phase 1 Error Amp Diff Amp Q S I-MIN FB + 38 25 LO1 I-MIN 5 PGOOD 50µA 24 PGN Q R + DACOUT 180° 18 VC2 S DAC VID_0 15 VID_1 14 POR DACOUT - 30mV ILIM 16 VS2 _ VID_3 12 VID_4 11 DACOUT UV S R S + 0.85 _ OV + 2.35 23 LO2 Fault S gm Bandgap S VDD VIN 6 S UVLO - 36 EA2 - PGOOD 100K 90K DACOUT IMAX + _ VIN 8 ROSC 9 VCC 19 VIN AMP FRQ OSC 0° 180° PGN 37 EO2 Phase 2 Integrating Amp 35mV offset 35mV offset + _ - 34 LP1 35 LP2 90K VCCL _IMIN 90K + VS3 90K Phase 2 Differential Amp + 13 + VID_2 PWGD 17 HO2 I-MAX Bandgap ENA 32 ILIM 33 ILIM3 ILIM1 Copyright 2000 Rev. 0.3, 2002-12-30 20 PGN3 21 I-Min 31 30 VS3 I-Max 29 VC3 ELECTRICALS GND 7 ILIM 10 ENA Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET APPLICATION CIRCUITS WWW . Microsemi .C OM Fig. 1 Typical VRM Application R2 61.9K C2 4700pF C1 4700pF UPS5817 C3 R7 Q3 IRF7811W 4700pF 2.00K R1 100K R6 4.02K 7 10uF 25V C7 8 R10 45.3K VBAT EN 9 10 11 12 PWRGD R13 100K 33 34 35 36 37 32 ILIM3 ILIM LP1 LP2 EA2- 38 FB+ VC3 EA1- VC1 DACOUT HO1 LX1676 CLQ PWRGD VS1 GND LO1 VIN PGN ROSC LO2 ENA VCCL VID4 I-MIN VID3 VCC 6 EO1 VC2 5 HO2 4 Q2 L3 70nh 0.22uF CR2 SK32 VS3 I-MAX VS2 4700pF NDS7002A DFOUT VID0 C4 3 VID1 2 Q1 VID2 R9 10K FB- EO2 U1 1 0.22uF CR1 SK32 R5 4.02K +5VP C5 C13 47uF 6.3V R4 4.02K C12 NDS7002A +5VP CR3 R3 61.9K PGN3 Q4 IRF7811W 31 30 29 28 27 CORE FB + +5VP CR4 26 CORE FB - 25 UPS5817 24 23 22 VBAT C11 C15 0.22uF 4.7uF6.3V 21 C10 20 4.7uF 6.3V Q5 IRF7811W C19 10uF 25V C20 10uF 25V C21 10uF 25V C105 10uF L1 VCORE 19 18 17 16 15 14 R14 100K 13 3.2uh R21 +5VP R15 100K R16 100K R17 100K 10.0 C8 4.7uF 6.3V Q7 IRF7822 Q6 IRF7822 C9 4.7uF 6.3V C25 VCORE RTN CR6 N/U +5VP CR5 VBAT 2.5V UPS5817 C17 0.22uF Q8 IRF7811W C22 10uF 25V C23 10uF 25V C24 10uF 25V C104 10uF L2 3.2uh VID(0) VID(1) VID(2) VID(3) VID(4) Q9 IRF7822 Q10 IRF7822 CR7 N/U Note: Q7,Q10 Optional C25 Several Capacitors Under Processor Socket +5VP VBAT C103 47uF 6.3V C18 10uF 25V APPLICATIONS Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 9 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET THEORY OF OPERATION POWER UP AND INITIALIZATION At power up, the LX1676 monitors the supply voltage to VCC and Vin, Before both supplies reach their undervoltage lock-out (UVLO) thresholds, a power on reset condition will prevent soft-start from beginning, the oscillator is disabled and all MOSFETs are kept off. SOFT-START Once the supplies are above the UVLO threshold and the Enable pin is brought high, the soft-start capacitor begins to be charged up by the reference DAC through the DACOUT pin. The capacitor voltage at the DACOUT pin rises as a linear ramp. The DACOUT pin is connected to the error amplifier’s non-inverting input which controls the output voltage. The output voltage will follow the DACOUT pin voltage. Phase 3 (hysteretic phase) is disabled during soft-start. Copyright 2000 Rev. 0.3, 2002-12-30 OVER-CURRENT PROTECTION (PHASE 1) The phase 1 current limit uses the RDS(ON) of the lower MOSFET, together with a resistor (RSET) to set the actual current limit point. The current limit comparator senses the current 400 nS after the lower MOSFET is switched on. A current source supplies a current (ISET), of 50µA which flows into RSET and determines the current limit trip point. The value of RSET is selected to set the current limit for the application. Phase 1 RSET is calculated by: RSET = ILimit • RDS(ON) 50µA The current limit comparator will trip when the drop across RSET equals the drop across the lower MOSFET RDS(ON)., at this time the comparator outputs a signal to set the I limit latch and removes the enable command. The Over-Current sensing is done on phase 1 only because phase 2 current is always being forced to equal the phase 1 current, therefore the current trip point is set at half of the desired current limit. For an output current limit setting of 30 amps, the current trip point for phase 1 is set at 15 amps. When the phase 1 over current latch is set all three phases are disabled, all MOSFETs are turned off. Vin 50 uA Q1 RSET + _ + _ Vout _ Iout RDS(ON) + Current Limit Comparator Q2 Q2 Current Flow 400nSec Delay Figure 3: Phase 1 Current Limit The delay before current limit is activated will result in current pulses exceeding the calculated values during the delay period if a short circuit is applied during that time. Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 APPLICATIONS OVER-CURRENT PROTECTION There are two separate current limit circuits in the LX1676. One looks at the phase 1 lower MOSFET drain current and the second looks at the phase 3 upper MOSFET drain current. Both circuits have a 400 nS delay before a current limit command is issued to the current limit latch, once set the current limit latch will hold all three phases off until it is reset. The Over-Current Protection is disabled during positive VID changes. To reset the current limit latch either the enable command (ENA) must be cycled low then back high or the input power must cycle off and then back on. WWW . Microsemi .C OM GENERAL DESCRIPTION The LX1676 is a voltage-mode pulse-width modulation controller integrated circuit. The PWM frequency is programmable from 200kHz to 1MHz. The device has external compensation, for more flexibility of the loop response. The LX1676 also makes use of a true differential input amplifier for remote voltage sensing at the actual processor core. This is a very important feature now that the core voltages are in the 1 to 2 volt range. The reference for the biphase PWM output is a 5 bit VID code DAC. The VID code DAC can generate a reference voltage of 0.925 to 2.000 volts. The output of the DAC is a bi-directional current source and is connected to the DACOUT pin. Connecting a capacitor from this pin to ground will generate a linear ramp, which will determine the rate of change of the output voltage. The rate of change can be set so that the current required to charge the total output capacitance is below the maximum current limit trip point. This will allow VID changes on the fly without tripping the over current sensor. LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET OVER-CURRENT PROTECTION (PHASE 3) The hysteretic phase has its own current limit protection because with it’s very fast response time with a 100 nH inductor the upper MOSFET cannot be allowed to stay on during an output short circuit condition. The phase 3 overcurrent sensing uses the RDS(ON) of the upper MOSFET with a resistor RSET to determine the over current limit point. A current source draws 50uA through RSET which determines the required drop across the MOSFET RDS(ON) to initiate a current limit condition. 50 uA ILIM3 +_ Vin _ RSET + Current Limit Comparator + RDS(ON) Q1 _ Vout VS3 400nS Delay Q2 FAULT LOGIC There are a number of possible states that will cause a fault condition that will disable the output MOSFET drivers. A fault condition will be caused by the following: Enable (ENA) pin being pulled low Over-current condition on either phase 1 or phase 3 Over Voltage output > 2.35V Under Voltage output < 0.85V WWW . Microsemi .C OM THEORY OF OPERATION (CONT) In all cases except Over Voltage all MOSFET drivers will be disabled. For an Over Voltage fault the lower MOSFETs for phase 1 and 2 will be held on to discharge the bulk capacitance on the output till a lower limit of .85 volts is reached then all MOSFETS will be turned off. To reset a fault it necessary to cycle the ENA pin low then back high or remove and reapply the input voltage VIN. The Under Voltage monitor is not enabled until the output voltage has ramped up to the level commanded by the DACOUT pin and the PWGD output in high. PWM FREQUENCY An external resistor sets the PWM frequency from the ROSC pin to ground. Figure 4 Phase 3 Current Limit Phase 3 RSET is calculated by: The equation for ROSC is: ILimit • RDSon Rset = 50uA ROSC = Copyright 2000 Rev. 0.3, 2002-12-30 1 K•f ) + 100e − 9 where ROSC is in KΩ, f is in Hz, K=105e-12 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 APPLICATIONS OVER VOLTAGE PROTECTION An over voltage protection circuit monitors the output voltage and will latch all three phases off if an over voltage condition (greater than 2.35 V) is detected. Both MOSFETs for phase 3 will be held off and the lower MOSFETs for phase 1 and 2 will be held on to discharge the output capacitor till the output voltage drops below .85 volt, at .85 volts all MOSFETs will be turned off. ( Page 11 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET The second feedback loop will use the output of the phase 1 LPF as a reference signal for an error amplifier that will compare this reference to the output of the phase 2 LPF. This error signal will be amplified and used to control the PWM circuit of phase 2. Therefore, the duty cycle of phase 2 will be set so that the equivalent voltage potential will be forced across the phase 2 inductor as compared to the phase 1 inductor. This will force the current in the phase 2 inductor to follow and equal the phase 1 inductor current. With the LoadSHARETM topology it is possible to imbalance the phases so that one phase will supply more current than the other under unique situations. The LX1676 will normally be used with the same supply voltages on phase 1 and 2 PWM inputs and will have equal currents in both phases. THEORY OF OPERATION FOR A BI-PHASE, LOADSHARETM CONFIGURATION The basic principle used in LoadSHARETM in a multiple phase buck converter topology is that if multiple, identical, inductors have the same identical voltage impressed across their leads, they must then have the same identical current passing through them. The current that we would like to balance between inductors is mainly the DC component along with as much as possible the transient current. All inductors in a multiphase buck converter topology have their output side tied together at the output filter capacitors. Therefore this side of all the inductors has the same identical voltage. If the input side of the inductors can be forced to have the same equivalent DC potential on this lead, then they will have the same DC current flowing. To achieve this requirement, phase 1 will be the control phase that sets the output operating voltage, under normal PWM operation. To force the current of phase 2 to be equal to the current of phase 1; a second feedback loop is used. Phase 2 has a low pass filter connected from the input side of each inductor. This side of the inductors has a square wave signal that is proportional to its duty cycle. The output of each LPF is a DC (+ some AC) signal that is proportional to the magnitude and duty cycle of its respective inductor signal. Fig. 5 WWW . Microsemi .C OM THEORY OF OPERATION (CONT) LoadSHARE Control Loop Phase 1 Low Pass Filter Phase 1 Diff Amp + - Differential Amp EA - LP2 180° Phase 2 Integrating Amp Ramp .75 V to 4 V Both PWMs + Phase 2 Comparator HO2 Vout APPLICATIONS - _ gm HO1 LO1 PWM + DC Bias Phase 1 Comparator + DC Bias + + _ PWM DACOUT DC Bias 0° - Differential Feedbach From Vout LP1 Phase 1 Error Amp LO2 EO2 Phase 2 Low Pass Filter Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 12 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET DACOUT +5 VB3 + Differential Feedback From Output FB - 35mV I-Max I-Max Comparator Vout VCCL VS3 70nH + Phase 3 is a Transient Correction Loop that can sum a large amount of current into the output node when required by an out of range condition. The differential feedback summing amplifier is connected directly to the output terminals and has sufficient bandwidth to follow any fast changes in output voltage. The feedback error voltage is compared to the commanded reference voltage (DACOUT) by two high speed comparators, I-Max and I-Min. The other inputs of these comparators are offset from the DACOUT as shown in Fig 6. If the error in output voltage exceeds the offset in either direction the appropriate MOSFET will be turned on to force current into or out of the output node to correct the voltage error. The very low value inductor (100nH) allows large amounts of current to be forced into or out of the output node very quickly. When the Transient Correction Loop is switching it forces the appropriate upper or lower MOSFETs in phases 1 and 2 to stay on (100% or 0% duty cycle) until the error is corrected. - TRANSIENT CORRECTION LOOP - The ramp shown in figure 5 is automatically adjusted to keep its amplitude fixed ratio to Vin over the range of 6 to 32 V input. This maintains a constant loop gain that is set by the feedback networks around the error amplifiers independent of PWM input voltage. The two drivers for the Transient Correction Loop have outputs (I-Max) and (I-Min) that may be used to drive a half bridge to correct for both low and high output voltage conditions. This permits pulling the output low if an overshoot occurs due to a rapid reduction in load current. With a conventional Buck regulator rapid changes in the negative direction are not possible due to the low voltage available as a forcing function. The two outputs (I-MAX and I-MIN) are completely independent. A single MOSFET and diode can be used to correct for voltage droop only or voltage overshoot only when driven by the appropriate output. If the I-MAX driver is not used the VB3 and VS3 pins must be connected to +5 volts. Under normal operation the Transient Correction phase is only active for a very brief time during high di/dt loads on the output. - LOOP GAIN AUTOMATIC COMPENSATION WWW . Microsemi .C OM THEORY OF OPERATION (CONT) FB + + 35mV I-Min I-Min Comparator PGN3 Figure 6: Phase 3 Transient Correction Loop APPLICATIONS Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 13 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET APPLICATION NOTE The allowed ESR can be found by: ( VRIPPLE = ESR × I RIPPLE VIN − VOUT L × D fs ∆I is the inductor ripple current, L is the output inductor value and ESR is the Effective Series Resistance of the output capacitor. ∆I should typically be in the range of 20% to 40% of the maximum output current. Higher inductance results in lower output voltage ripple, allowing slightly higher ESR to satisfy the transient specification. Higher inductance also slows the inductor current slew rate in response to the loadcurrent step change, ∆I, resulting in more output-capacitor voltage droop. When using electrolytic capacitors, the capacitor voltage droop is usually negligible, due to the large capacitance The inductor-current rise and fall times are: TRISE = L× (V ∆I IN − VOUT ) and TFALL = L× ∆I ∆I × D fs I RMS = I L d(0.5 − d) for d < 0.5 OUTPUT CAPACITOR The output capacitor is sized to meet ripple and transient performance specifications. Effective Series Resistance (ESR) is a critical parameter. When a step load current occurs, the output voltage will have a step that equals the product of the ESR and the current step, ∆I. In an advanced Copyright 2000 Rev. 0.3, 2002-12-30 Where IL is the inductor current and d is the duty cycle. The maximum RMS value of 0.25IL will occur when d = 25% or 75%. Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 14 APPLICATIONS VIN − VOUT Where IRIPPLE is the inductor ripple current, ∆I is the maximum load current step change, and VEX is the allowed output voltage excursion in the transient. Electrolytic capacitors can be used for the output capacitor, but are less stable with age than tantalum capacitors. As they age, their ESR degrades, reducing the system performance and increasing the risk of failure. It is recommended that multiple parallel capacitors be used, so that, as ESR increase with age, overall performance will still meet the processor’s requirements. There is frequently strong pressure to use the least expensive components possible, however, this could lead to degraded long-term reliability, especially in the case of filter capacitors. Microsemi’s demonstration boards use the CDE Polymer AL-EL (ESRE) filter capacitors, which are aluminum electrolytic, and have demonstrated reliability. The OS-CON series from Sanyo generally provides the very best performance in terms of long term ESR stability and general reliability, but at a substantial cost penalty. The CDE Polymer AL-EL (ESRE) filter series provides excellent ESR performance at a reasonable cost. Beware of off-brand, very low-cost filter capacitors, which have been shown to degrade in both ESR and general electrolytic characteristics over time. INPUT CAPACITOR The input capacitor and the input inductor, if used, are to filter the pulsating current generated by the buck converter to reduce interference to other circuits connected to the same 5V rail. In addition, the input capacitor provides local de-coupling for the buck converter. The capacitor should be rated to handle the RMS input current requirement. The RMS input current is: VOUT . The inductance value can be calculated by: L= ) ESR × I RIPPLE + ∆I < VEX where ∆I = microprocessor power supply, the output capacitor is usually selected from ESR instead of capacitance or RMS current capability. A capacitor that satisfies the ESR requirements usually has a larger capacitance and current capability than strictly needed WWW . Microsemi .C OM OUTPUT INDUCTOR The output inductor should be selected to meet the requirements of the output voltage ripple in steady-state operation and the inductor current slew-rate during transient. The peak-to-peak output voltage ripple is: LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET APPLICATION NOTE PROGRAMMING THE OUTPUT VOLTAGE Output voltage is determined by the internal 5 bit DAC. The DAC inputs are the Voltage Identification (VID) 0-4 lines, the VID table lists the available output voltages for the corresponding VID codes. There are no external resistor dividers to program output voltage and only the steps listed are available. WWW . Microsemi .C OM SOFT-START CAPACITOR An external soft-start capacitor is connected to the DACOUT pin and will be charged at a linear rate by the internal 50uA bi-directional current source after the UVLO circuit has been satisfied. Whenever the VID code is changed during normal operation the soft-start capacitor will determine the rate of change at the output. APPLICATIONS Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 15 LX1676 I N T E G R A T E D Mobile AMD Athlon VRM Controller P R O D U C T S P RELIMINARY D ATA S HEET PACKAGE DIMENSIONS WWW . Microsemi .C OM LQ 38-Pin Micro Leadframe Package (MLPQ) D C C 1 2 3 Dim A B C D E F G H I E P F G MILLIMETERS MIN MAX 0.20 REF .18 .30 .18 .18 5.00 BSC 3.00 3.25 5.00 5.25 0.50 BSC 0 0.05 0.70 0.80 INCHES MIN MAX 0.0078 REF 0.007 0.011 0.007 .007 .196 BSC 0.118 0.127 .196 .206 0.019 BSC 0 0.019 0.027 0.031 MILLIMETERS MIN MAX 0.85 0.95 0.19 0.25 0.09 0.20 9.60 9.80 4.30 4.50 0.50 BSC 0.05 0.15 – 1.10 0.50 0.75 0° 8° 6.25 6.50 – 0.10 INCHES MIN MAX 0.033 0.037 0.19 0.009 0.003 0.008 0.378 0.390 0.169 0.176 0.0196 BSC 0.002 0.005 – 0.043 0.020 0.030 0° 8° 0.246 0.256 – 0.004 I B H PW A 38-Pin Thin Small Shrink Outline (TSSOP) 1 19 P 20 38 F M A H G B L C Note: 1. Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006”) on any side. Lead dimension shall not include solder coverage. Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 16 MECHANICALS E D Dim A B C D E F G H L M P *LC LX1676 I N T E G R A T E D P R O D U C T S Mobile AMD Athlon VRM Controller P RELIMINARY D ATA S HEET WWW . Microsemi .C OM NOTES NOTES PRODUCT PRELIMINARY DATA – Information contained in this document is pre-production data, and is proprietary to Microsemi. It may not be modified in any way without the express written consent of Microsemi. Product referred to herein is not guaranteed to achieve preliminary or production status and product specifications, configurations, and availability may change at any time. Copyright 2000 Rev. 0.3, 2002-12-30 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 17