LT1580/LT1580-2.5 7A, Very Low Dropout Regulator U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ The LT ®1580 is a 7A low dropout regulator designed to power the new generation of microprocessors. The dropout voltage of this device is 100mV at light loads rising to just 540mV at 7A. To achieve this dropout, a second low current input voltage 1V greater than the output voltage, is required. The device can also be used as a single supply device where dropout is comparable to an LT1584. Low Dropout, 540mV at 7A Output Current Fast Transient Response Remote Sense 1mV Load Regulation Fixed 2.5V Output and Adjustable Output No Supply Sequencing Problems in Dual Supply Mode U APPLICATIONS ■ ■ ■ ■ ■ ■ Several other new features have been added to the LT1580. A remote SENSE pin is brought out. This feature virtually eliminates output voltage variations due to load changes. Typical load regulation, measured at the SENSE pin, for a load current step of 100mA to 7A is less than 1mV. Microprocessor Supplies Post Regulators for Switching Supplies High Current Regulators 5V to 3.XXV for Pentium® Processors Operating at 90MHz to 166MHz and Beyond 3.3V to 2.9V for Portable Pentium Processor PowerPCTM Series Power Supplies The LT1580 has fast transient response, equal to the LT1584. On fixed voltage devices, the ADJ pin is brought out. A small capacitor on the ADJ pin further improves transient response. This device is ideal for generating processor supplies of 2V to 3V on motherboards where both 5V and 3.3V supplies are available. , LTC and LT are registered trademarks of Linear Technology Corporation. Pentium is a registered trademark of Intel Corporation. PowerPC is a trademark of IBM Corporation. U TYPICAL APPLICATION Dropout Voltage — Minimum Power Voltage 2.5V Microprocessor Supply 5V 0.2A 2.5V/7A VOUT VPOWER + + 330µF OS-CON LT1580-2.5 VCONTROL + 10µF TANT GND 100µF TANT AVX TPS ×7 SENSE ADJ 0.1µF MINIMUM POWER VOLTAGE (V) 3.3V 7A 1.0 INDICATES GUARANTEED TEST POINTS 0°C ≤ TJ ≤ 125°C DATA SHEET LIMIT 0.5 TJ = 125°C TJ = 25°C 1580 TA01 0 0 1 3 5 4 2 OUTPUT CURRENT (A) 6 7 1580 G03 1 LT1580/LT1580-2.5 U W W W ABSOLUTE MAXIMUM RATINGS Power Transistor LT1580C ............................................ 0°C to 150°C LT1580I ........................................ – 40°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C UU U VPOWER Input Voltage ................................................ 6V VCONTROL Input Voltage ........................................... 13V Storage Temperature ............................ – 65°C to 150°C Operating Junction Temperature Range Control Section LT1580C............................................ 0°C to 125°C LT1580I ........................................ – 40°C to 125°C PRECONDITIONING 100% Thermal Limit Functional Test U W U PACKAGE/ORDER INFORMATION FRONT VIEW TAB IS OUTPUT 5 VPOWER 4 VCONTROL 3 VOUT 2 ADJ 1 SENSE ORDER PART NUMBER LT1580CQ LT1580IQ FRONT VIEW TAB IS OUTPUT 5 VPOWER 4 VCONTROL 3 VOUT 2 ADJ 1 SENSE Q PACKAGE 5-LEAD PLASTIC DD T PACKAGE 5-LEAD PLASTIC TO-220 θJA = XX°C/ W θJA = 50°C/ W FRONT VIEW 7 6 5 4 3 2 1 TAB IS OUTPUT NC VPOWER ADJ VOUT VCONTROL GND SENSE ORDER PART NUMBER LT1580CR-2.5 LT1580IR-2.5 FRONT VIEW TAB IS OUTPUT NC VPOWER ADJ VOUT VCONTROL GND SENSE 7 6 5 4 3 2 1 R PACKAGE 7-LEAD PLASTIC DD T7 PACKAGE 7-LEAD PLASTIC TO-220 θJA = XX°C/ W θJA = 50°C/ W ORDER PART NUMBER LT1580CT LT1580IT ORDER PART NUMBER LT1580CT7-2.5 LT1580IT7-2.5 Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS PARAMETER Output Voltage: LT1580-2.5 Reference Voltage: LT1580 (VADJ = 0V) Line Regulation: LT1580-2.5 LT1580 2 (Note 1) CONDITIONS VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 0mA VCONTROL = 4V to 12V, VPOWER = 3V to 5.5V, ILOAD = 0mA to 4A VCONTROL = 4V to 12V, VPOWER = 3V to 5.5V, ILOAD = 0mA to 7A, 0°C ≤ TJ ≤ 125°C VCONTROL = 4V to 12V, VPOWER = 3V to 5.5V, ILOAD = 0mA to 6.5A, – 40°C ≤ TJ < 0°C VCONTROL = 2.75V, VPOWER = 2V, ILOAD = 10mA VCONTROL = 2.7V to 12V, VPOWER = 1.75V to 5.5V, ILOAD = 10mA to 4A VCONTROL = 2.7V to 12V, VPOWER = 2.05V to 5.5V, ILOAD = 10mA to 7A, 0°C ≤ TJ ≤ 125°C VCONTROL = 2.7V to 12V, VPOWER = 2.05V to 5.5V, ILOAD = 10mA to 6.5A, – 40°C ≤ TJ < 0°C VCONTROL = 3.65V to 12V, VPOWER = 3V to 5.5V, ILOAD = 10mA VCONTROL = 2.5V to 12V, VPOWER = 1.75V to 5.5V, ILOAD = 10mA ● ● ● ● MIN 2.485 2.475 2.475 TYP 2.500 2.500 2.500 MAX 2.515 2.525 2.525 UNITS V V V 2.460 2.500 2.525 V 1.243 1.237 1.237 1.250 1.250 1.250 1.257 1.263 1.263 V V V 1.232 1.250 1.263 V 1 1 3 3 mV mV LT1580/LT1580-2.5 ELECTRICAL CHARACTERISTICS PARAMETER Load Regulation: LT1580-2.5 LT1580 (VADJ = 0V) CONDITIONS VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 0mA to 7A VCONTROL = 2.75V, VPOWER = 2.1V, ILOAD = 10mA to 7A ● ● Minimum Load Current: LT1580 VCONTROL = 5V, VPOWER = 3.3V, VADJ = 0V (Note 3) ● Control Pin Current: LT1580-2.5 (Note 4) VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 4A, – 40°C ≤ TJ < 0°C VCONTROL = 5V, VPOWER = 3V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C VCONTROL = 5V, VPOWER = 3V, ILOAD = 4A, – 40°C ≤ TJ < 0°C VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C Control Pin Current: LT1580 (Note 4) MIN TYP 1 1 5 10 mA 10 12 60 70 70 80 120 130 mA mA mA mA mA mA mA mA 10 12 60 70 70 80 120 130 mA mA mA mA mA mA mA mA 6 10 mA 50 120 µA 33 60 6 30 33 60 Ground Pin Current: LT1580-2.5 VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 0mA ● ADJ Pin Current: LT1580 (VADJ = 0V) VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 10mA ● Current Limit: LT1580-2.5 VCONTROL = 5V, VPOWER = 3.3V, ∆VOUT = 100mV, 0°C ≤ TJ ≤ 125°C VCONTROL = 5V, VPOWER = 3.3V, ∆VOUT = 100mV, – 40°C ≤ TJ < 0°C VCONTROL = 2.75V, VPOWER = 2.05V, ∆VOUT = 100mV, 0°C ≤ TJ ≤ 125°C VCONTROL = 2.75V, VPOWER = 2.05V, ∆VOUT = 100mV, – 40°C ≤ TJ < 0°C 7.1 6.6 7.1 6.6 8 Ripple Rejection: LT1580-2.5 LT1580 VC = VP = 5V Avg, VRIPPLE = 1VP-P, IOUT = 4A, TJ = 25°C VC = VP = 3.75V Avg, VRIPPLE = 1VP-P, VADJ = 0V, IOUT = 4A, TJ = 25°C 60 60 80 80 Thermal Regulation 30ms Pulse 0.002 Thermal Resistance, Junction-to-Case T, T7 Packages, Control Circuitry/Power Transistor 0.65/2.70 LT1580 (VADJ = 0V) UNITS mV mV 6 30 VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 4A, – 40°C ≤ TJ < 0°C VCONTROL = 2.75V, VPOWER = 1.75V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C VCONTROL = 2.75V, VPOWER = 1.75V, ILOAD = 4A, – 40°C ≤ TJ < 0°C VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C MAX 5 5 A A A A 8 dB dB 0.020 %/W °C/W Dropout Voltage (Note 2) Minimum VCONTROL: LT1580-2.5 (VCONTROL – VOUT) Minimum VCONTROL: LT1580 (VCONTROL – VOUT) (VADJ = 0V) VPOWER = 3.3V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C VPOWER = 3.3V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C VPOWER = 3.3V, ILOAD = 1A, 0°C ≤ TJ ≤ 125°C VPOWER = 3.3V, ILOAD = 1A, – 40°C ≤ TJ < 0°C VPOWER = 3.3V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C VPOWER = 3.3V, ILOAD = 4A, – 40°C ≤ TJ < 0°C VPOWER = 3.3V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C VPOWER = 3.3V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C 1.00 VPOWER = 2.05V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C VPOWER = 2.05V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C VPOWER = 2.05V, ILOAD = 1A, 0°C ≤ TJ ≤ 125°C VPOWER = 2.05V, ILOAD = 1A, – 40°C ≤ TJ < 0°C VPOWER = 2.05V, ILOAD = 2.75A, 0°C ≤ TJ ≤ 125°C VPOWER = 2.05V, ILOAD = 2.75A, – 40°C ≤ TJ < 0°C VPOWER = 2.05V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C VPOWER = 2.05V, ILOAD = 4A, – 40°C ≤ TJ < 0°C VPOWER = 2.05V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C VPOWER = 2.05V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C 1.00 1.00 1.06 1.15 1.00 1.05 1.06 1.15 1.15 1.20 1.15 1.20 1.20 1.25 1.30 1.35 V V V V V V V V 1.15 1.20 1.15 1.20 1.18 1.23 1.20 1.25 1.30 1.35 V V V V V V V V V V 3 LT1580/LT1580-2.5 ELECTRICAL CHARACTERISTICS PARAMETER Minimum VPOWER: LT1580-2.5 (VPOWER – VOUT) CONDITIONS VCONTROL = 5V, ILOAD = 100mA VCONTROL = 5V, ILOAD = 1A VCONTROL = 5V, ILOAD = 4A, TJ = 25°C VCONTROL = 5V, ILOAD = 4A VCONTROL = 5V, ILOAD = 7A, TJ = 25°C VCONTROL = 5V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C VCONTROL = 5V, ILOAD = 6.5A, – 40°C ≤ TJ ≤ 0°C Minimum VPOWER: LT1580 (VPOWER – VOUT) (VADJ = 0V) MIN ● ● ● 0.54 0.70 0.70 VCONTROL = 2.75V, ILOAD = 100mA VCONTROL = 2.75V, ILOAD = 1A VCONTROL = 2.75V, ILOAD 2.75A VCONTROL = 2.75V, ILOAD = 4A, TJ = 25°C VCONTROL = 2.75V, ILOAD = 4A VCONTROL = 2.75V, ILOAD = 7A, TJ = 25°C VCONTROL = 2.75V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C VCONTROL = 2.75V, ILOAD = 6.5A, – 40°C ≤ TJ ≤ 0°C The ● denotes specifications which apply over the full operating temperature range. Note 1: Unless otherwise specified VOUT = VSENSE. For the LT1580 adjustable device VADJ = 0V. Note 2: For the LT1580, dropout is caused by either minimum control voltage (VCONTROL) or minimum power voltage (VPOWER). Both parameters are specified with respect to the output voltage. The specifications represent the minimum input/output voltage required to maintain 1% regulation. TYP 0.10 0.15 0.34 0.10 0.15 0.26 0.34 ● ● ● ● 0.54 0.70 0.70 MAX 0.17 0.22 0.40 0.50 0.62 0.80 0.80 UNITS V V V V V V V 0.17 0.22 0.38 0.40 0.50 0.62 0.80 0.80 V V V V V V V V Note 3: For the LT1580 adjustable device the minimum load current is the minimum current required to maintain regulation. Normally the current in the resistor divider used to set the output voltage is selected to meet the minimum load current requirement. Note 4: The control pin current is the drive current required for the output transistor. This current will track output current with roughly a 1:100 ratio. The minimum value is equal to the quiescent current of the device. U W TYPICAL PERFORMANCE CHARACTERISTICS Control Pin Current vs Output Current 140 2 100 DATA SHEET LIMIT 80 TYPICAL DEVICE 60 40 20 0 0 1 4 3 5 2 OUTPUT CURRENT (A) 6 7 1580 G01 INDICATES GUARANTEED TEST POINTS 0°C ≤ TJ ≤ 125°C MINIMUM POWER VOLTAGE (V) MINIMUM CONTROL VOLTAGE (VCONTROL – VOUT) (V) CONTROL PIN CURRENT (mA) 1.0 INDICATES GUARANTEED TEST POINTS 0°C ≤ TJ ≤ 125°C 120 4 Dropout Voltage — Minimum Power Voltage Minimum Control Voltage DATA SHEET LIMIT 1 TJ = 125°C TJ = 25°C 0 0 1 3 5 4 2 OUTPUT CURRENT (A) 6 7 1580 G02 INDICATES GUARANTEED TEST POINTS 0°C ≤ TJ ≤ 125°C DATA SHEET LIMIT 0.5 TJ = 125°C TJ = 25°C 0 0 1 3 5 4 2 OUTPUT CURRENT (A) 6 7 1580 G03 LT1580/LT1580-2.5 U W TYPICAL PERFORMANCE CHARACTERISTICS LT1580-2.5 Output Voltage vs Temperature 1.258 2.508 1.256 2.506 1.254 2.504 OUTPUT VOLTAGE (V) REFERENCE VOLTAGE (V) LT1580 Reference Voltage vs Temperature 1.252 1.250 1.248 LOAD 2.498 1.244 2.494 25 50 75 100 125 150 TEMPERATURE (°C) 7A 2.500 2.496 0 VOUT 50mV/DIV 2.502 1.246 1.242 –50 –25 2.492 –50 –25 400mA 50µs/DIV 0 1580 TA02 25 50 75 100 125 150 TEMPERATURE (°C) 1580 G04 U U U PIN FUNCTIONS Load Current Step Response 1580 G05 (5-Lead/7-Lead) SENSE (Pin 1): This pin is the positive side of the reference voltage for the device. With this pin it is possible to Kelvin sense the output voltage at the load. ADJ (Pin 2/5): This pin is the negative side of the reference voltage for the device. Transient response can be improved by adding a small bypass capacitor from the ADJ pin to ground. For fixed voltage devices the ADJ pin is also brought out to allow the user to add a bypass capacitor. GND (Pin 2, 7-Lead Only): For fixed voltage devices this is the bottom of the resistor divider that sets the output voltage. VPOWER (Pin 5/6): This is the collector to the power device of the LT1580. The output load current is supplied through this pin. For the device to regulate, the voltage at this pin must be between 0.1V and 0.8V greater than the output voltage (see Dropout specifications). VCONTROL (Pin 4/3): This pin is the supply pin for the control circuitry of the device. The current flow into this pin will be about 1% of the output current. For the device to regulate, the voltage at this pin must be between 1.0V and 1.3V greater than the output voltage (see Dropout specifications). VOUT (Pin 3/4): This is the power output of the device. 5 LT1580/LT1580-2.5 W BLOCK DIAGRA VCONTROL VPOWER + – SENSE VOUT FOR FIXED VOLTAGE DEVICE 1580 BD ADJ GND U W U U APPLICATIONS INFORMATION The LT1580 is a low dropout regulator designed to power the new generation of microprocessors. Low dropout regulators have become more common in desktop computer systems as microprocessor manufacturers have moved away from 5V only CPUs. A wide range of supply requirements exists today with new voltages just over the horizon. In many cases the input-output differential is very small, effectively disqualifying many of the low dropout regulators on the market today. The LT1580 is designed to make use of multiple power supplies, present in most systems, to reduce the dropout voltage. This two supply approach maximizes efficiency. The second supply, at least 1V greater than the output voltage, is used to provide power for the control circuitry and supply the drive current to the NPN output transistor. This allows the NPN to be driven into saturation, thereby 6 reducing the dropout voltage by a VBE compared to conventional designs. The current requirement for the control voltage is relatively small, equal to approximately 1% of the output current or about 70mA for a 7A load. The bulk of this current is drive current for the NPN output transistor. This drive current becomes part of the output current. The control voltage must be at least 1V greater than the output voltage to obtain optimum performance. The maximum voltage on the VCONTROL pin is 13V. The maximum voltage at the VPOWER pin is limited to 7V. GDN pin current for fixed voltage devices is 6mA (typ) and is constant as a function of load. ADJ pin current for adjustable devices is 60µA at 25°C and varies proportional to absolute temperature. LT1580/LT1580-2.5 U W U U APPLICATIONS INFORMATION The LT1580 has improved frequency compensation which permits the use of capacitors with very low ESR. This is critical in addressing the needs of modern, low voltage, high speed microprocessors. Current generation microprocessors cycle load current from several hundred milliamperes to several amperes in tens of nanoseconds. Output voltage tolerances are tighter and include transient response as part of the specification. The LT1580 is designed to meet the fast current load step requirements of these microprocessors and saves total cost by needing less output capacitance to maintain regulation. Careful design has eliminated any supply sequencing issues associated with a dual supply system. The output voltage will not turn on until both supplies are operating. If the control voltage comes up first, the output current will be limited to a few milliamperes until the power input voltage comes up. If the power input comes up first the output will not turn on at all until the control voltage comes up. The output can never come up unregulated. The LT1580 can also be operated as a single supply device by tying the control and power inputs together. Dropout in single supply operation will be determined by the minimum control voltage. The LT1580 includes several innovative features that require additional pins over the traditional 3-terminal regulator. Both the fixed and adjustable devices have remote SENSE pins, permitting very accurate regulation of output voltage at the load, where it counts, rather than at the regulator. As a result the typical load regulation over an output current range of 100mA to 7A with a 2.5V output is typically less than 1mV. For the fixed voltage devices the ADJ pin is also brought out. This allows the user to improve transient response by bypassing the internal resistor divider. In the past fixed output voltage devices did not provide this capability. Bypassing the ADJ pin with a capacitor in the range of 0.1µF to 1µF will provide optimum transient response. The value chosen will depend on the amount of output capacitance in the system. In addition to the enhancements mentioned above the reference accuracy has been improved by a factor of two with a guaranteed initial tolerance of ±0.6% at 25°C. Temperature drift is also very well controlled. When com- bined with ratiometrically accurate internal divider resistors the part can easily hold 1% output accuracy over the full temperature range and load current range, guaranteed, while operating with an input/output differential of well under 1V. Typical applications for the LT1580 include 3.3V to 2.5V conversion with a 5V control supply, 5V to 4.2V conversion with a 12V control supply or 5V to 3.6V conversion with a 12V control supply. It is easy to obtain dropout voltages of less than 0.5V at 4A along with excellent static and dynamic specifications. The LT1580 is capable of 7A of output current with a maximum dropout of 0.8V. The LT1580 has fast transient response that allows it to handle the large current changes associated with today’s microprocessors. The device is fully protected against overcurrent and overtemperature conditions. Both fixed voltage (2.5V) and adjustable output versions are available. The device is available in a multilead TO-220 package with five leads for the adjustable device and seven leads for the fixed voltage device. Grounding and Output Sensing The LT1580 allows true Kelvin sensing for both the high and low side of the load. This means that the voltage regulation at the load can be easily optimized. Voltage drops due to parasitic resistances between the regulator and the load which would normally degrade regulation can be placed inside the regulation loop of the LT1580. Figures 1 through 3 illustrate the advantages of remote sensing. Figure 1 shows the LT1580 connected as a conventional 3-terminal regulator with the SENSE lead connected directly to the output of the device. RP represents the parasitic resistance of the connections between the LT1580 and the load. The load is typically a microprocessor and RP is made up of the PC traces and/or connector resistances, in the case of a modular regulator, between the regulator and the processor. The effect of RP can be seen in trace A of Figure 3. Very small resistances cause significant load regulation steps. For example, at 7A output current the output voltage will shift by 7mV for every 0.001Ω of resistance. In Figure 2 the LT1580 is connected to take advantage of the remote sense feature. The SENSE 7 LT1580/LT1580-2.5 U U W U APPLICATIONS INFORMATION pin and the top of the resistor divider are connected to the top of the load. The bottom of the resistor divider is connected to the bottom of the load. RP is now effectively connected inside the regulating loop of the LT1580 and the load regulation at the load will be negligible for reasonable 5V VCONTROL 3.3V SENSE VPOWER LT1580 values of RP. Trace B of Figure 3 illustrates the effect on output regulation. It is important to note that the voltage drops due to RP are not eliminated. They will add to the dropout voltage of the regulator regardless of whether they are inside the loop as in Figure 2 or outside the loop as in Figure 1. This means that the LT1580 can control the voltage at the load as long as the input-output voltage is greater than the total of the dropout voltage of the LT1580 plus the voltage drop across RP. Stability VOUT ADJ + RP LOAD R1 VOUT R2 RP – The LT1580 requires the use of an output capacitor as part of the device frequency compensation. The device requires a minimum of 22µF tantalum or 150µF of aluminum electrolytic to ensure stability. Larger capacitor values increase stability and improve transient performance. 1580 F01 Many different types of capacitors are available and have widely varying characteristics. These capacitors differ in capacitor tolerance (sometimes up to ±100%), equivalent series resistance, equivalent series inductance and capacitance temperature coefficient. The LT1580 frequency compensation optimizes frequency response with low ESR capacitors. In general, use capacitors with an ESR of less than 1Ω. Figure 1. Conventional Load Sensing 5V VCONTROL 3.3V SENSE VPOWER LT1580 VOUT ADJ + RP LOAD R1 VOUT R2 RP – 1580 F02 Figure 2. Remote Load Sensing (∆IOUT)(RP) VOUT FIGURE 1 Bypassing the adjust terminal on the LT1580 improves ripple rejection and transient response. The ADJ pin is brought out on the fixed voltage device specifically to allow this capability. VOUT FIGURE 2 IOUT TIME 1580 F03 Figure 3. Remote Sensing Improves Load Regulation 8 For microprocessor applications larger value capacitors will be needed to meet the transient requirements of the processor. Processor manufacturers require tight voltage tolerances on the power supply. High quality bypass capacitors must be used to limit the high frequency noise generated by the processor. Multiple small ceramic capacitors in addition to high quality bulk tantalum capacitors are typically required to limit parasitic inductance (ESL) and resistance (ESR) in the capacitors to acceptable levels. The LT1580 is stable with the type of capacitors recommended by processor manufacturers. Capacitor values on the order of several hundred microfarads are used to ensure good transient response with heavy LT1580/LT1580-2.5 U W U U APPLICATIONS INFORMATION load current changes. Output capacitance can increase without limit and larger values of output capacitance further improve the stability and transient response of the LT1580. Modern microprocessors generate large high frequency current transients. The load current step contains higher order frequency components that the output coupling network must handle until the regulator throttles to the load current level. Capacitors are not ideal elements and contain parasitic resistance and inductance. These parasitic elements dominate the change in output voltage at the beginning of a transient load step change. The ESR of the output capacitors produces an instantaneous step in output voltage (∆V = ∆I)(ESR). The ESL of the output capacitors produces a droop proportional to the rate of change of the output current (V = L)(∆I/∆t). The output capacitance produces a change in output voltage proportional to the time until the regulator can respond (∆V = ∆t)(∆I/ C). These transient effects are illustrated in Figure 4 . Output Voltage The adjustable version of the LT1580 develops a 1.25V reference voltage between the SENSE pin and the ADJ pin (see Figure 5). Placing a resistor R1 between these two terminals causes a constant current to flow through R1 and down through R2 to set the overall output voltage. Normally R1 is chosen so that this current is the specified minimum load current of 10mA. The current out of the ADJ pin adds to the current from R1. The ADJ pin current is small, typically 50µA. The output voltage contribution of the ADJ pin current is small and only needs to be considered when very precise output voltage setting is required. Note that the top of the resistor divider should be connected directly to the SENSE pin for best regulation. See the section on grounding and Kelvin sensing above. VCONTROL + VCONTROL VPOWER + VPOWER VOUT + VOUT LT1580 ESR EFFECTS SENSE ESL EFFECTS ADJ CAPACITANCE EFFECTS VREF R1 1580 F04 SLOPE, V ∆I = t C POINT AT WHICH REGULATOR TAKES CONTROL ( ) IADJ = 50µA R2 VOUT = VREF 1 + R2 + IADJ (R2) R1 1580 F05 Figure 4 Figure 5. Setting Output Voltage The use of capacitors with low ESR, low ESL and good high frequency characteristics is critical in meeting the output voltage tolerances of these high speed microprocessors. These requirements dictate a combination of high quality, surface mount, tantalum and ceramic capacitors. The location of the decoupling network is critical to transient performance. Place the decoupling network as close to the processor pins as possible because trace runs from the decoupling capacitors to the processor pins are inductive. The ideal location for the decoupling network is actually inside the microprocessor socket cavity. In addition, use large power and ground plane areas to minimize distribution drops. Protection Diodes In normal operation the LT1580 does not require protection diodes. Older 3-terminal regulators require protection diodes between the VOUT pin and the Input pin or between the ADJ pin and the VOUT pin to prevent die overstress. On the LT1580, internal resistors limit internal current paths on the ADJ pin. Therefore even with bypass capacitors on the ADJ pin, no protection diode is needed to ensure device safety under short-circuit conditions. The ADJ pin can be driven on a transient basis ±7V with respect to the output without any device degradation. 9 LT1580/LT1580-2.5 U W U U APPLICATIONS INFORMATION A protection diode between the VOUT pin and the VPOWER pin is usually not needed. An internal diode between the VOUT pin and the VPOWER pin on the LT1580 can handle microsecond surge currents of 50A to 100A. Even with large value output capacitors it is difficult to obtain those values of surge currents in normal operation. Only with large values of output capacitance, such as 1000µF to 5000µF, and with the VPOWER pin instantaneously shorted to ground can damage occur. A crowbar circuit at the power input can generate those levels of current, and a diode from output to power input is then recommended. This is shown in Figure 6. Normal power supply cycling or system “hot plugging and unplugging” will not do any damage. VCONTROL + D1* VCONTROL VPOWER + VOUT VPOWER D2* + VOUT LT1580 SENSE ADJ *OPTIONAL DIODES: 1N4002 R1 R2 1580 F06 Figure 6. Optional Clamp Diodes Protect Against Input Crowbar Circuits A protection diode between the VOUT pin and the VCONTROL pin is usually not needed. An internal diode between the VOUT pin and the VCONTROL pin on the LT1580 can handle microsecond surge currents of 1A to 10A. This can only occur if the VCONTROL pin is instantaneously shorted to ground with a crowbar circuit with large value output capacitors. Since the VCONTROL pin is usually a low current supply, this condition is unlikely. A protection diode from the VOUT pin to the VCONTROL pin is recommended if the VCONTROL pin can be instantaneously shorted to ground. This is shown in Figure 6. Normal power supply cycling or system “hot plugging and unplugging” will not do any damage. 10 If the LT1580 is connected as a single supply device with the VCONTROL and VPOWER input pins shorted together the internal diode between the VOUT and the VPOWER input pin will protect the VCONTROL input pin. Like any other regulator exceeding the maximum input to output differential can cause the internal transistors to break down and none of the internal protection circuitry is then functional. Thermal Considerations The LT1580 has internal current and thermal limiting designed to protect the device under overload conditions. For continuous normal load conditions maximum junction temperature ratings must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. This includes junction-to-case, case-to-heat sink interface and heat sink resistance itself. Thermal resistance specifications are given in the electrical characteristics for both the Control section and the Power section of the device. The thermal resistance of the Control section is given as 0.65°C/W and junction temperature of the Control section is allowed to run at up to 125°C. The thermal resistance of the Power section is given as 2.7°C/W and the junction temperature of the Power section is allowed to run at up to 150°C. The difference in thermal resistances between Control and Power sections is due to thermal gradients between the power transistor and the control circuitry. Virtually all of the power dissipated by the device is dissipated in the power transistor. The temperature rise in the power transistor will be greater than the temperature rise in the Control section so the effective thermal resistance, temperature rise per watt dissipated, will be lower in the Control section. At power levels below 12W the temperature gradient will be less than 25°C and the maximum ambient temperature will be determined by the junction temperature of the Control section. This is due to the lower maximum junction temperature in the Control section. At power levels greater than 12W the temperature gradient will be greater than 25°C and the maximum ambient temperature will be determined by the Power section. For both cases the junction temperature is determined by the total power dissipated in the device. For most LT1580/LT1580-2.5 U W U U APPLICATIONS INFORMATION low dropout applications the power dissipation will be less than 12W. The power in the device is made up of two main components: the power in the output transistor and the power in the drive circuit. The additional power in the control circuit is negligible. The power in the drive circuit will be equal to: PDRIVE = (VCONTROL – VOUT)(ICONTROL) where ICONTROL is equal to between IOUT/100 (typ) and IOUT/58 (max). ICONTROL is a function of output current. A curve of ICONTROL vs IOUT can be found in the Typical Performance Characteristics curves. The power in the output transistor is equal to: POUTPUT = (VPOWER – VOUT)(IOUT) The total power is equal to: PTOTAL = PDRIVE + POUTPUT Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly below the die. This is the lowest resistance path for heat flow. Proper mounting is required to ensure the best possible thermal flow from this area of the package to the heat sink. Thermal compound at the case-to-heat sink interface is strongly recommended. If the case of the device must be electronically isolated, a thermally conductive spacer can be used as long as the added contribution to thermal resistance is considered. Please consult Linear Technology’s “ Mounting Considerations for Power Semiconductors,” 1990 Linear Applications Handbook, Volume 1, Pages RR3-1 to RR3-20. Note that the case of the LT1580 is electrically connected to the output. The following example illustrates how to calculate maximum junction temperature. Using an LT1580 and assuming: VCONTROL (max continuous) = 5.25V (5V + 5%), VPOWER (max continuous) = 3.465V (3.3V + 5%), VOUT = 2.5V, Iout = 4A, TA = 70°C, θHEATSINK = 4°C/W, θCASE-HEATSINK = 1°C/W (with thermal compound) Power dissipation under these conditions is equal to: Total Power Dissipation = PDRIVE + POUTPUT PDRIVE = (VCONTROL – VOUT) (ICONTROL) ICONTROL = IOUT/58 = 4A/58 = 69mA PDRIVE = (5.25V – 2.5V)(69mA) = 190mW POUTPUT = (VPOWER – VOUT)(IOUT) = ( 3.465V – 2.5V)(4A) = 3.9W Total Power Dissipation = 4.05W Junction temperature will be equal to: TJ = TA + PTOTAL (θHEATSINK + θCASE-HEATSINK + θJC) For the Control section: TJ = 70°C + 4.05W(4°C/W +1°C/W + 0.65°C/W) = 93°C 93°C < 125°C = TJMAX for Control Section For the Power section: TJ = 70°C + 4.05W (4°C/W + 1°C/W + 2.7°C/W) = 101°C 101°C < 150°C = TJMAX for Power Section In both cases the junction temperature is below the maximum rating for the respective sections, ensuring reliable operation. 11 LT1580/LT1580-2.5 U TYPICAL APPLICATION 2.5V/6A Regulator 5V 5 3.3V VCONT VPOWER SENSE LT1580 ADJ C3 22µF 25V + + C2 220µF 10V C4 0.33µF RTN 2 VOUT 4 1 VOUT = 2.5V 3 VCC R1 110Ω 1% C1 R2 110Ω 100µF 10V 1% + 100µF 10V ×2 + 1µF 25V × 10 MICROPROCESSOR SOCKET VSS 1580 TA03 12 LT1580/LT1580-2.5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. Q Package 5-Lead Plastic DD Pak (LTC DWG # 05-08-1461) 0.256 (6.502) 0.060 (1.524) 0.060 (1.524) TYP 0.390 – 0.415 (9.906 – 10.541) 0.165 – 0.180 (4.191 – 4.572) 0.045 – 0.055 (1.143 – 1.397) 15° TYP 0.060 (1.524) 0.183 (4.648) 0.059 (1.499) TYP 0.330 – 0.370 (8.382 – 9.398) ( +0.008 0.004 –0.004 +0.203 0.102 –0.102 ) 0.095 – 0.115 (2.413 – 2.921) 0.075 (1.905) 0.300 (7.620) ( +0.012 0.143 –0.020 +0.305 3.632 –0.508 BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK ) 0.057 – 0.077 (1.447 – 1.955) 0.028 – 0.038 (0.711 – 0.965) 0.050 ± 0.012 (1.270 ± 0.305) 0.013 – 0.023 (0.330 – 0.584) Q(DD5) 0396 R Package 7-Lead Plastic DD Pak (LTC DWG # 05-08-1462) 0.256 (6.502) 0.060 (1.524) 0.060 (1.524) TYP 0.390 – 0.415 (9.906 – 10.541) 0.165 – 0.180 (4.191 – 4.572) 15° TYP 0.060 (1.524) 0.183 (4.648) 0.059 (1.499) TYP 0.330 – 0.370 (8.382 – 9.398) BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK ( +0.008 0.004 –0.004 +0.203 0.102 –0.102 ) 0.095 – 0.115 (2.413 – 2.921) 0.075 (1.905) 0.300 (7.620) 0.045 – 0.055 (1.143 – 1.397) ( +0.012 0.143 –0.020 +0.305 3.632 –0.508 ) 0.040 – 0.060 (1.016 – 1.524) 0.026 – 0.036 (0.660 – 0.914) 0.013 – 0.023 (0.330 – 0.584) 0.050 ± 0.012 (1.270 ± 0.305) R (DD7) 0396 13 LT1580/LT1580-2.5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. T Package 5-Lead Plastic TO-220 (Standard) (LTC DWG # 05-08-1421) 0.390 – 0.415 (9.906 – 10.541) 0.165 – 0.180 (4.191 – 4.572) 0.147 – 0.155 (3.734 – 3.937) DIA 0.045 – 0.055 (1.143 – 1.397) 0.230 – 0.270 (5.842 – 6.858) 0.460 – 0.500 (11.684 – 12.700) 0.570 – 0.620 (14.478 – 15.748) 0.330 – 0.370 (8.382 – 9.398) 0.620 (15.75) TYP 0.700 – 0.728 (17.78 – 18.491) 0.152 – 0.202 0.260 – 0.320 (3.861 – 5.131) (6.60 – 8.13) 0.095 – 0.115 (2.413 – 2.921) 0.013 – 0.023 (0.330 – 0.584) 0.057 – 0.077 (1.448 – 1.956) 0.028 – 0.038 (0.711 – 0.965) 0.135 – 0.165 (3.429 – 4.191) 0.155 – 0.195 (3.937 – 4.953) T5 (TO-220) 0398 14 LT1580/LT1580-2.5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. T7 Package 7-Lead Plastic TO-220 (Standard) (LTC DWG # 05-08-1422) 0.390 – 0.415 (9.906 – 10.541) 0.165 – 0.180 (4.191 – 4.572) 0.147 – 0.155 (3.734 – 3.937) DIA 0.045 – 0.055 (1.143 – 1.397) 0.230 – 0.270 (5.842 – 6.858) 0.460 – 0.500 (11.684 – 12.700) 0.570 – 0.620 (14.478 – 15.748) 0.330 – 0.370 (8.382 – 9.398) 0.620 (15.75) TYP 0.700 – 0.728 (17.780 – 18.491) 0.152 – 0.202 0.260 – 0.320 (3.860 – 5.130) (6.604 – 8.128) 0.040 – 0.060 (1.016 – 1.524) 0.095 – 0.115 (2.413 – 2.921) 0.013 – 0.023 (0.330 – 0.584) 0.026 – 0.036 (0.660 – 0.914) 0.135 – 0.165 (3.429 – 4.191) 0.155 – 0.195 (3.937 – 4.953) T7 (TO-220) (FORMED) 1197 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LT1580/LT1580-2.5 U TYPICAL APPLICATION Dual Regulators Power Pentium Processor or Upgrade CPU R12 0.0075Ω* 5V + 12V R1 10k C8 0.1µF VOUT VIN C1 220µF 10V D1 1N4148 R2 470Ω LT1006 R10 10k + C9 220µF 10V + C4 0.33µF 5V D2 1N4148 12V R13 0.005Ω* R4 178Ω 1% C6 0.01µF C11 22µF 35V C2 220µF 10V 4 + VCONTROL SENSE R11 10k R14, 2Ω 1 C10 1µF LT1580 5 VPOWER VOUT ADJ + 3 R7 107Ω 0.25% R6 89.8Ω 0.5% R8 107Ω 0.35% Q3 2N7002 5V Q1 ZVN4206 Q3 2N7002 R5 10k R9 10k E3 TO CPU VOLTAGE SELECT PIN Q2 2N3904 *RESISTORS ARE IMPLEMENTED AS COPPER TRACES ON PCB IF 1 OZ COPPER, TRACE WIDTHS ARE 0.05 INCH IF 2 OZ COPPER, TRACE WIDTHS ARE 0.025 INCH R13 IS 0.83 INCHES LONG, R12 IS 1.24 INCHES LONG CORE SUPPLY 3.5V/2.5V C7 330µF 6.3V 2 C5 0.33µF C3 220µF 10V R3 110Ω 1% ADJ + – + LT1587 I/O SUPPLY 3.5V/3.3V E3 CPU TYPE 0 P55C 1 P54C 1580 TA04 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC 1266 Synchronous Switching Controller >90% Efficient High Current Microprocessor Supply LTC1267 Dual High Efficiency Synchronous Switching Regulator >90% Efficiency with Fixed 5V, 3.3V or Adjustable Outputs LTC1430 High Power Synchronous Step-Down Switching Regulator >90% Efficient High Current Microprocessor Supply LT1584 7A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors LT1585 4.6A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors LT1587 3A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors ® 16 Linear Technology Corporation 158025fa LT/GP 0598 2K REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1995