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LTC1702/LTC1703 Dual 550kHz Synchronous 5V-to-2.x/1.xV Switching Regulator Controllers with VID
December 1998
FEATURES
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DESCRIPTION
The LTC(R)1702/LTC1703 are dual switching regulator controllers optimized for high efficiency with low input voltages. Each includes two complete, independent switching regulator controllers on-chip, designed to drive a pair of external N-channel MOSFET devices in a voltage mode feedback, synchronous buck configuration. The LTC1703 includes digital output voltage adjustment at controller 1 that conforms to the Intel Mobile VID specification. The LTC1702/ LTC1703 use a constant-frequency, true PWM design switching at 550kHz, minimizing external component size and cost and maximizing load transient performance. The synchronous buck architecture automatically shifts to discontinous and then to Burst ModeTM operation as the output load decreases, ensuring 90% or greater efficiency over a wide range of load currents. The LTC1702/LTC1703 feature onboard references trimmed to 0.5% and can provide better than 1% regulation at the converter outputs. An optional latching FAULT mode protects the load if the output rises 15% above the intended voltage. Each channel can be enabled independently; with both channels disabled, the LTC1702/LTC1703 shut down and supply current drops below 100A.
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Two Independent Controllers in One Package LTC1703 Side 1 Output Is Compliant with the Intel Mobile VID Specification Two Sides Run Out-of-Phase to Minimize CIN All N-Channel External MOSFET Architecture No External Current Sense Resistor Excellent Output Regulation: 1% Initial Accuracy over Line and Load 550kHz Switching Frequency Minimizes External Component Size 1A to >20A Output Current per Channel 90% Efficiency over Wide Load Current Range Quiescent Current Drops Below 100A in Shutdown Small SSOP Packages
APPLICATIONS
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Microprocessor Core/IO Supplies Multiple Logic Supply Generator Distributed Power Applications High Efficiency Power Conversion
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
VOUT1 0.9V TO 2V 15A 1F L1 0.33H D05022HC M11 IRF7805 M21A IRF7805
Dual Output VID/1.8V Converter
DCP1 MBR0520LT1 1F DCP2 MBR0520LT1 M12 NDS8926
RIMAX2 20k M21B IRF7805 1 2 CCP1 1F 3 4 5 RIMAX1,18.7k 6 7 8 9 10 C21 C11 11 15pF 220pF 12 13 R31, 10k 14 VID0 VID1 VID2 VID3 VID4 28 PVCC IMAX2 27 BOOST1 BOOST2 26 BG1 BG2 25 TG1 TG2 24 SW1 SW2 23 IMAX1 PGND 22 FCB FAULT 21 RUN/SS1 RUN/SS2 20 COMP1 COMP2 19 SGND FB2 18 FB1 VCC 17 VID4 SENSE 16 VID3 VID0 15 VID2 VID1 LTC1703 CCP2 1F
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COUT1 180F 4V x6
MBRD835L
M22 NDS8926
GND
CSS1 0.22F
R21 100k C31 220pF
R22, 100k C22 15pF
1F
Specifications on this data sheet are preliminary only, and subject to change without notice. Contact the manufacturer before finalizing a design using this part.
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VIN 5V
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1F L2 2.2H D03316P-222
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CIN 150F 6V x2 VOUT2 1.8V 3A
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COUT2 180F 4V RB2 8.06k R12 10.2k
C32 2200pF R32 1k 10
1F
GND GND
FAULT OUTPUT C12 220pF
1703 TA01
CSS2 0.22F
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LTC1702/LTC1703
ABSOLUTE MAXIMUM RATINGS
Supply Voltage VCC ........................................................................ 7V BOOSTn ............................................................... 15V BOOSTn - SWn .................................................... 7V Input Voltage SWn ........................................................ - 1V to 15V All Other Inputs ......................... - 0.3V to VCC + 0.3V
PACKAGE/ORDER INFORMATION
TOP VIEW PVCC BOOST1 BG1 TG1 SW1 IMAX1 PWRGD1 FCB RUN/SS1 1 2 3 4 5 6 7 8 9 24 IMAX2 23 BOOST2 22 BG2 21 TG2 20 SW2 19 PGND 18 PWRGD2 17 FAULT 16 RUN/SS2 15 COMP2 14 FB2 13 VCC
ORDER PART NUMBER LTC1702CGN
COMP1 10 SGND 11 FB1 12
GN PACKAGE 24-LEAD NARROW PLASTIC SSOP (150mil)
TJMAX = 125C, JA = 100C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VCC PVCC BVCC ICC IPVCC IBOOST VFB VFB PARAMETER VCC Supply Voltage PVCC Supply Voltage BOOST Pin Voltage VCC Supply Current PVCC Supply Current BOOST Pin Current Feedback Voltage Feedback Voltage Line Regulation Main Control Loop
VCC = 5V, TA = 25C unless otherwise specified. (Note 2)
MIN TYP MAX 7 UNITS V V V mA A mA A mA A 0.804 0.5 V %
CONDITIONS
(Note 3) VBOOST - VSW (Note 3) RUN/SS1 = RUN/SS2 = VCC RUN/SS1 = RUN/SS2 = 0V (Note 5) RUN/SS1 = RUN/SS2 = VCC (Note 4) RUN/SS1 = RUN/SS2 = 0V (Note 5) RUN/SS1 = RUN/SS2 = VCC (Note 4) RUN/SS1 = RUN/SS2 = 0V (Note 5) RUN/SS1 = RUN/SS2 = VCC VCC = 2.7V to 7V 0.796 6 20 5 20 3 0.1 0.8
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(Note 1)
Peak Output Current TGn, BGn .............................................................. 1A Operating Temperature Range .................... 0C to 70C Junction Temperature........................................... 150C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
TOP VIEW PVCC BOOST1 BG1 TG1 SW1 IMAX1 FCB RUN/SS1 COMP1 1 2 3 4 5 6 7 8 9 28 IMAX2 27 BOOST2 26 BG2 25 TG2 24 SW2 23 PGND 22 FAULT 21 RUN/SS2 20 COMP2 19 FB2 18 VCC 17 VID4 16 VID3 15 VID2
ORDER PART NUMBER LTC1703CG
SGND 10 FB1 11 SENSE 12 VID0 13 VID1 14
G PACKAGE 28-LEAD PLASTIC SSOP (209mil)
TJMAX = 125C, JA = 85C/ W
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LTC1702/LTC1703
ELECTRICAL CHARACTERISTICS
SYMBOL IFB VOUT VFCB VFCB IFCB VRUN ISS fOSC OSC2 DCMIN1 DCMIN2 DCMAX tNOV t r, tf AVFB GBW IFB VMIN VMAX AVL IIMAX Status Outputs VPWRGD VOLPG IPG tPG VFAULT VOLF IFAULT tFAULT RFB-SENSE RPULLUP VIDT IVID-LEAK VPULLUP PWRGD Trip Point PWRGD Output Low Voltage PWRGD Output Leakage PWRGD Delay Time FAULT Trip Point FAULT Output Low Voltage FAULT Output Current FAULT Delay Time Resistance Between SENSE and FB PARAMETER Feedback Current Output Voltage Load Regulation FCB Threshold FCB Feedback Hysteresis FCB Pin Current RUN Pin Threshold Soft Start Source Current Oscillator Frequency Converter 2 Oscillator Phase Minimum Duty Cycle Minimum Duty Cycle Maximum Duty Cycle Driver Nonoverlap Driver Rise/Fall Time FB DC Gain FB Gain Bandwidth FB Sink/Source Current MIN Comparator Threshold MAX Comparator Threshold ILIM Gain IMAX Source Current
VCC = 5V, TA = 25C unless otherwise specified. (Note 2)
MIN TYP 0.1 0.79 0.8 10 1 0.5 MAX 1 0.3 0.81 UNITS A % V mV A V A kHz DEG % % 90 25 15 CL = 10pF, RL = 10k 65 25 10 775 825 35 100 % ns ns dB MHz mA mV mV dB A % 0.4 1 V A s % 0.4 V A s k 0.25 40 0.4 1.6 0.01 2.8 4.5 1 % k V V A V V
CONDITIONS (Note 6)
RUN/SSn = 0.5V 475 Relative to Converter 1 VFB < VMAX VFB > VMAX 0
-3 550 180 10
Switching Characteristics
Feedback Amplifier CL = 10pF, RL = 10k
Current Limit Loop IMAX = 0V -10 -3 IPWRGD = 1mA 0.2 0.1 100 + 15 IFAULT = 1mA VFAULT = 0V 0.2 - 10 10 10 Programmed from 0.9V to 2V VDIODE = 0.6V (Note 7) VIL (2.7V VCC 5.5V) VIH (2.7V VCC 5.5V) VCC < VID < 7V (Note 7) VCC = 3.3V VCC = 5V - 0.25
VID Inputs (LTC1703 Controller 1 Only) VOUT Error % Output Voltage Accuracy VID Input Pull-Up Resistance VID Input Voltage Threshold VID Input Leakage Current VID Pull-Up Voltage
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LTC1702/LTC1703
ELECTRICAL CHARACTERISTICS
VCC = 5V, TA = 25C unless otherwise specified. (Note 2)
Note 5: Supply current in shutdown is dominated by external MOSFET leakage and may be significantly higher than the quiescent current drawn by the LTC1702/LTC1703, especially at elevated temperature. If any of the VIDn pins are grounded in shutdown, the VCC supply current will rise and be approximately equal to the number of grounded VIDn pins times (VCC - 0.6V)/40k. Note 6: This parameter is guaranteed by correlation and is not tested directly. Note 7: Each built-in pull-up resistor attached to the VID inputs also has a senses diode connected to VCC to allow input voltages higher than the VCC supply without damage or clamping. (See Applications Information section for further detail.) Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to ground unless otherwise specified. Note 3: PVCC and BVCC (VBOOST - VSW) must be greater than VGS(ON) of the external MOSFETs used to ensure proper operation. Note 4: Supply current in normal operation is dominated by the current needed to charge and discharge the external MOSFET gates and will be higher than the quiescent current drawn by the LTC1702/LTC1703. This current will vary with supply voltage and the external MOSFETs used.
PIN FUNCTIONS
Note: Pin numbers are listed as (LTC1702 pin/LTC1703 pin)
PVCC (Pin 1/1): Driver Power Supply Input. PVCC provides power to the two BGn output drivers. PVCC must be connected to a voltage high enough to fully turn on the external MOSFETs M21 and M22. PVCC should generally be connected directly to VIN. PVCC requires at least a 1F bypass capacitor directly to PGND. BOOST1 (Pin 2/2): Controller 1 Top Gate Driver Supply. The BOOST1 pin supplies power to the floating TG1 driver. BOOST1 should be bypassed to SW1 with a 1F capacitor. An additional Schottky diode from VIN to BOOST1 pin will create a complete floating charge-pumped supply at BOOST1. No other external supplies are required. BG1 (Pin 3/3): Controller 1 Bottom Gate Drive. The BG1 pin drives the gate of the bottom N-channel synchronous switch MOSFET, M21. BG1 is designed to drive up to 10,000pF of gate capacitance directly. If RUN/SS1 goes low, BG1 will go low, turning off M21. If FAULT mode is tripped, BG1 will go high and stay high, keeping M21 on until the power is cycled. TG1 (Pin 4/4): Controller 1 Top Gate Drive. The TG1 pin drives the gate of the top N-channel MOSFET, M11. The TG1 driver draws power from the BOOST1 pin and returns to the SW1 pin, providing true floating drive to M11. TG1 is designed to drive up to 10,000pF of gate capacitance directly. In shutdown or fault modes, TG1 will go low. SW1 (Pin 5/5): Controller 1 Switching Node. SW1 should be connected to the switching node of converter 1. The TG1 driver ground returns to SW1, providing floating gate
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drive to the top N-channel MOSFET switch, M11. The voltage at SW1 is compared to IMAX1 by the current limit comparator while the bottom MOSFET, M21, is on. IMAX1 (Pin 6/6): Controller 1 Current Limit Set. The IMAX1 pin sets the current limit comparator threshold for controller 1. If the voltage drop across the bottom MOSFET, M21, exceeds the magnitude of the voltage at IMAX1, controller 1 will go into current limit. The IMAX1 pin has an internal 10A current source pull-up, allowing the current threshold to be set with a single external resistor to PGND. PWRGD1 (Pin 7/NA): Controller 1 Power Good. PWRGD1 is an open-drain logic output. PWRGD1 will pull low whenever VOUT1 falls 3% below its programmed value. When RUN/SS1 is low (side 1 shut down), PWRGD1 will go high. The LTC1703 does not have PWRGD pins. FCB (Pin 8/7): Force Continuous Bar. The FCB pin forces both converters to maintain continuous synchronous operation regardless of load when the voltage at FCB drops below 0.8V. FCB is normally tied to VCC. To force continuous operation, tie FCB to SGND, FCB can also be connected to a feedback resistor divider from a secondary winding on one converter's inductor to generate a third regulated output voltage. RUN/SS1 (Pin 9/8): Controller 1 Run/Soft Start. Pulling RUN/SS1 to SGND will disable controller 1 and turn off both of its external MOSFET switches. Pulling both RUN/SS pins down will shut down the entire LTC1702, dropping the quiescent supply current to below 100A. A capacitor from RUN/SS1 to SGND will control the turn-on
LTC1702/LTC1703
PIN FUNCTIONS
and rate of rise of the controller 1 output voltage at powerup. An internal 10A current source pull-up at the RUN/SS1 pin sets the turn-on time at approximately 150ms/F. COMP1 (Pin 10/9): Controller 1 Loop Compensation. The COMP1 pin is connected directly to the output of the first controller's error amplifier and the input to the PWM comparator. An RC network is used at the COMP1 pin to compensate the feedback loop for optimum transient response. SGND (Pin 11/10): Signal Ground. All internal low power circuitry returns to the SGND pin. Connect to a low impedance ground, separated from the PGND node. All feedback, compensation and soft start connections should return to SGND. SGND and PGND should connect only at a single point, near the PGND pin and the negative plate of the VIN bypass capacitor. FB1 (Pin 12/11): Controller 1 Feedback Input. On the LTC1702, FB1 should be connected through a resistor divider to VOUT1 to set the output voltage. The loop compensation network for controller 1 also connects to FB1. In the LTC1703, FB1 is connected to the internal VID network, and should only be connected to the compensation network. SENSE (NA/Pin 12): Output Sense. Connect to VOUT1. The LTC1702 does not include a SENSE pin. VID0 to VID4 (NA/Pins 13 to 17): VID Programming Inputs. These are logic inputs that set the output voltage at side 1 to a preprogrammed value (see Table 1). VID4 is the MSB, VID0 is the LSB. The codes selected by the VIDn inputs correspond to the Intel Mobile VID specification. Each VIDn pin includes an on-chip 40k pull-up resistor in series with a diode (see Block Diagram). The LTC1702 does not include VID pins. VCC (Pin 13/18): Power Supply Input. All internal circuits except the output drivers are powered from this pin. VCC should be connected to a low noise power supply voltage between 2.7V and 7V, and should be bypassed to SGND with at least an 0.1F capacitor in close proximity to the LTC1702/LTC1703. FB2 (Pin 14/19): Controller 2 Feedback Input. FB2 should be connected through a resistor divider to VOUT2 to set the output voltage. The loop compensation network for controller 2 also connects to FB2. The FB2 pin on the LTC1703 is completely independent from the VID programming circuitry and works in the same manner as FB1 and FB2 on the LTC1702. COMP2 (Pin 15/20): Controller 2 Loop Compensation. See COMP1. RUN/SS2 (Pin 16): Controller 2 Run/Soft Start. See RUN/SS1. FAULT (Pin 17/22): Output Overvoltage Fault (Latched). The FAULT pin is an open-drain output with an internal 10A pull-up. If either regulated output voltage rises more than 15% above its programmed value, for more than 10s, the FAULT output will go high, the entire LTC1702/ LTC1703 will be disabled, and both BG pins will go high, turning on the bottom MOSFET switches and pulling down the high output voltage. The LTC1702/LTC1703 will remain latched in this state until the power is cycled. When FAULT mode is active, the FAULT pin will be pulled up with an internal 10A current source. Tying FAULT directly to PGND will disable FAULT mode and will cause the LTC1702/ LTC1703 to ignore overvoltage faults. PWRGD2 (Pin 18/NA): Controller 2 Power Good. See PWRGD1. The LTC1703 does not have PWRGD pins. PGND (Pin 19/23): Power Ground. The BGn drivers return to this pin. Connect PGND to a high current ground node in close proximity to the sources of external MOSFETs, M21 and M22, and the VIN and VOUT bypass capacitors. SW2 (Pin 20/24): Controller 2 Switching Node. See SW1. TG2 (Pin 21/25): Controller 2 Top Gate Drive. See TG1. BG2 (Pin 22/26): Controller 2 Bottom Gate Drive. See BG1. BOOST2 (Pin 23/27): Controller 2 Top Gate Driver Supply. See BOOST1. IMAX2 (Pin 24/28): Controller 2 Current Limit Set. See IMAX1.
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LTC1702/LTC1703
BLOCK DIAGRAM
VCC BURST LOGIC DRIVE LOGIC
90% DUTY CYCLE OSC 550kHz DIS
RUN/SS1,2 COMP1,2
SOFT START
ILIM + IMAX1,2
800mV
SHUTDOWN TO THIS CONTROLLER 40k 500mV SHUTDOWN TO ENTIRE CHIP VCC VID0 40k VCC FROM OTHER CONTROLLER VID1 40k VCC VID2 40k VCC VID3 40k VCC VID4 SWITCH CONTROL LOGIC RB1 R11 10k TO FB1 SENSE LTC1703 ONLY
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FCB PVCC BOOST1,2 TG1,2 SW1,2 BG1,2 PGND SGND 100s DELAY 10s DELAY FB - MIN MAX FLT FROM OTHER CONTROLLER PWRGD1,2 FAULT 775mV 825mV 920mV FB1,2
1702/03 BD
LTC1702/LTC1703
VID PROGRA
00000 00001 00010 00011 00100 00101 00110 00111 01000 01001 01010 01011 01100 01101 01110 01111 GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND Float Float Float Float Float Float Float Float
Table 1. VID Inputs and Corresponding Output Voltage CODE VID4 VID3 VID2 VID1 VID0
GND GND GND GND Float Float Float Float GND GND GND GND Float Float Float Float GND GND Float Float GND GND Float Float GND GND Float Float GND GND Float Float GND Float GND Float GND Float GND Float GND Float GND Float GND Float GND Float
APPLICATIONS INFORMATION
The LTC1702/LTC1703 are dual, step-down (buck), voltage mode feedback synchronous switching regulator controllers. The LTC1702 has two adjustable outputs, while the LTC1703 adds digital output voltage control to side 1. Both parts are designed to operate from a low voltage input supply (7V maximum) and provide high power, high efficiency, precisely regulated output voltages. Several features make the LTC1702/LTC1703 particularly suited for microprocessor supply regulation. Output regulation is extremely tight, with DC line and load regulation and initial accuracy better than 1%, and total regulation including transient response inside of 3% with a properly designed circuit. The 550kHz switching frequency allows the use of physically small, low value external components without compromising performance. The 800mV internal reference allow regulated output voltages as low as 800mV. The LTC1702/LTC1703 synchronous switching logic can transition automatically into discontinuous and Burst Mode operation, maximizing efficiency with light loads. An onboard overvoltage (OV) fault flag indicates when an OV fault has occurred. The OV flag can be set to latch the device off when an OV fault has occurred, or to automatically resume operation when the fault is removed. The LTC1702 also includes a Power Good output for each channel to indicate when the output voltage is in regulation. The LTC1702/LTC1703 run from low input voltages and generate two lower output voltages at very high current. Their strengths are small size, peerless regulation and transient response and high efficiency. This combination makes it ideal for providing multiple low voltage logic supplies to microprocessors or high density ASICs in systems using a "2-step" regulation architecture, often used in portable and advanced desktop computers. 2-Step Conversion "2-step" architectures use a primary regulator to convert the input power source (batteries or AC line voltage) to an intermediate supply voltage, often 5V. This intermediate voltage is then converted to the low voltage, high current supplies required by the system using a secondary regulator-- the LTC1702/LTC1703. 2-step conversion eliminates the need for a single converter that converts a high input voltage to a very low output voltage--often an
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I G CODES
VOUT1
2.00V 1.95V 1.90V 1.85V 1.80V 1.75V 1.70V 1.65V 1.60V 1.55V 1.50V 1.45V 1.40V 1.35V 1.30V 1.25V
CODE
10000 10001 10010 10011 10100 10101 10110 10111 11000 11001 11010 11011 11100 11101 11110 11111
VID4
Float Float Float Float Float Float Float Float Float Float Float Float Float Float Float Float
VID3
GND GND GND GND GND GND GND GND Float Float Float Float Float Float Float Float
VID2
GND GND GND GND Float Float Float Float GND GND GND GND Float Float Float Float
VID1
GND GND Float Float GND GND Float Float GND GND Float Float GND GND Float Float
VID0
GND Float GND Float GND Float GND Float GND Float GND Float GND Float GND Float
VOUT1
1.275V 1.250V 1.225V 1.200V 1.175V 1.150V 1.125V 1.100V 1.075V 1.050V 1.025V 1.000V 0.975V 0.950V 0.925V 0.900V
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LTC1702/LTC1703
APPLICATIONS INFORMATION
awkward design challenge. It also fits naturally into systems that continue to use the 5V supply to power portions of their circuitry, or have excess 5V capacity available as newer circuit designs shift the current load to lower voltage supplies. Each regulator in a typical 2-step system maintains a relatively low step-down ratio (5:1 or less), running at high efficiency while maintaining a reasonable duty cycle. In contrast, a regulator taking a single step from a high input voltage to a 1.xV or 2.xV output must run at a very narrow duty cycle, mandating trade-offs in external component values and compromising efficiency and transient response. The efficiency loss can exceed that of using a 2-step solution. Further complicating the calculation is the fact that many systems draw a significant fraction of their total power off the 5V supply, not the low voltage supply. 2-step solutions using the LTC1702/LTC1703 usually match or exceed the total system efficiency of 1-step solutions, and provide the additional benefits of improved transient response, reduced PCB area and simplified power trace routing. 2-step regulation can buy advantages in thermal management as well. Power dissipation in the LTC1702/LTC1703 portion of a 2-step circuit is lower than it would be in a typical 1-step converter, even in cases where the 1-step converter has higher total efficiency than the 2-step system. In a typical microprocessor core supply regulator, for example, the regulator is usually located right next to the CPU. In a 1-step design, all of the power dissipated by the core regulator is right there next to the hot CPU, aggravating thermal management. In a 2-step LTC1702/LTC1703 design, a significant percentage of the power lost in the core regulation system happens in the 5V supply, which is usually away from the CPU. The power lost to heat in the LTC1702/LTC1703 section of the system is relatively low, minimizing the heat near the CPU. Fast Transient Response The LTC1702/LTC1703 use an internal 25MHz GBW op amp as an error amplifier. This allows the compensation network to be designed with several poles and zeros in a more flexible configuration than a typical gm feedback amplifier. The high bandwidth of the amplifier, coupled with the high 550kHz switching frequency and the low values of the external inductor and output capacitor, allow very high loop crossover frequencies. The low inductor value is the other half of the equation--with a typical value under 1H, the inductor allows very fast di/dt slew rates. The result is superior transient response compared with conventional solutions. High Efficiency The LTC1702/LTC1703 use a synchronous step-down (buck) architecture, with two external N-channel MOSFETs per output. A floating topside driver and a simple external charge pump provide full gate drive to the upper MOSFET. The voltage mode feedback loop and MOSFET VDS current limit sensing remove the need for an external current sense resistor, eliminating an external component and a source of power loss in the high current path. Properly designed circuits using low gate charge MOSFETs are capable of efficiencies exceeding 90% over a wide range of output voltages and currents. LTC1703 VID Programming The LTC1703 includes an onboard feedback network that programs the output voltage at side 1 in accordance with the Intel Mobile VID specification (Table 1). The network includes a 10k resistor (R11) connected from SENSE to FB1, and a variable value resistor (RB1) from FB1 to SGND, with the value set by the digital code present at the VID4 ~ VID0 pins. SENSE should be connected to VOUT1 to allow the network to monitor the output voltage. No additional feedback components are required to set the output voltage at controller 1, although loop compensation components are still required. Each VIDn pin includes an internal 40k pull-up resistor, allowing it to float high if left unconnected. The pull-up resistors are connected to VCC through diodes (see Block Diagram), allowing the VIDn pins to be pulled above VCC without damage. Note that codes 01111 and 11111, defined by Intel to indicate "no CPU present," do generate output voltages at VOUT1 (1.25V and 0.9V, respectively). Note also that controller 2 on the LTC1703 is not connected to the VID circuitry, and works in exactly the same manner as the LTC1702.
17023p LT/TP 1298 500 * PRINTED IN USA
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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(c) LINEAR TECHNOLOGY CORPORATION 1998

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