LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products November 1999 Positive High Voltage Hot Swap Controller-- LT1641 Product of the Month Low Noise, Micropower, Low Dropout Regulators Withstand Reverse Voltage--LT1762 and LT1763 The LT(R)1762 and LT1763 are very low noise, low dropout linear regulators. The LT1762 is rated for 150mA of output current, whereas the LT1763 is rated for 500mA. For supply flexibility and good efficiency, the input voltage of these regulators can be as low as 350mV (maximum dropout voltage) above the output at maximum rated current. The regulators are designed for use in battery-powered systems with 25A operating current for the LT1762 and 30A for the LT1763. Both regulators feature a 0.1A shutdown state. Quiescent current is well controlled for these devices; it does not rise in dropout--when the input to output voltage differential is below the dropout rating--as is the case with many other regulators. The LT1762 and LT1763 regulators feature low noise operation. With the addition of an external 0.01F bypass capacitor, output voltage noise over the 10Hz to 100kHz bandwidth is reduced to < 30VRMS (Figures 1 and 2). Both regulators can operate with output capacitors as low in value as 2.2F for the LT1762 and 4.7F for the LT1763. Small ceramic capacitors can be used with either device without the need for additional series resistance as is common VIN 3.7V TO 20V IN 1F with other regulators. Internal protection circuitry on both regulators includes reversebattery protection, current limiting, thermal limiting and reverse-current protection. No protection diodes are required. Both regulators are available in fixed output voltages of 2.5V, 3V, 3.3V and 5V or as an adjustable device with an output range of 1.22V to 20V. The LT1762 is packaged in an 8-lead MSOP and the LT1763 is available in an 8-lead SO package. These regulators can be paralleled for more output current if required. 160 COUT = 10F IL = 150mA f = 10Hz TO 100kHz 140 OUTPUT NOISE (VRMS) LT1762-5 120 LT1762-3.3 100 LT1762-3 80 60 LT1762 40 LT1762-2.5 20 0 10 100 1000 CBYP (pF) Vol. 8 No. 11 When a circuit board is inserted into a live backplane, the supply bypass capacitors on the board draw high peak currents from the backplane power bus as they charge. The transient currents can permanently damage the connector pins and cause glitches on the system supply, causing other boards in the system to reset. The LT1641 is designed to turn on a board's supply voltage in a controlled manner (Figure 1), allowing the board to be safely inserted into or removed from a live backplane. A high side switch driver controls an N-channel pass transistor in the power path (Q1 in Figure 2) for supply voltages ranging from 9V to 80V. The LT1641 is tested and guaranteed to be safe from damage with supply voltages up to 100V and may be connected directly to 24V and 48V supplies without floating grounds or level shifting of logic signals. The device provides undervoltage and overcurrent protection and a power good signal that indicates when the output supply voltage is ready. It comes in an 8-lead SO package. 10000 1762 G42 Figure 2. LT1762 RMS Output Noise vs Bypass Capacitor OUT + SENSE LT1762-3.3 3.3V AT 150mA 20VRMS NOISE 10F 0.01F SHDN BYP GND 1762 TA01 Figure 1. 3.3V Low Noise Regulator Inside This Issue: Micropower Current Sense Amp Operates from 2.5V to 60V with 40V Offset Error--LT1787 ............................................................................................. High Efficiency Linear and Switching Solutions for Splitting a Digital Supply--LT1118 and LTC1504 ................................................................................ High Efficiency PolyPhaseTM DC/DC Current Mode Controllers Provide 20A to 200A Using Surface Mount Components--LTC1629/LTC1929 ....................................................... A 10-Bit Voltage Output Micropower DAC in a Tiny SOT-23 Package--LTC1663 ................ Linear Technology Chronicle * November 1999 Figure 1. LT1641 Power-Up Waveforms 2 Continued on page 2 3 3 4 , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap, Over-The-Top, PolyPhase and OPTI-LOOP are trademarks of Linear Technology Corporation. I2C is a trademark of Philips Electronics N.V. 1 LT1641 from page 1 Short-Circuit Protection To prevent excessive power dissipation in the pass transistor and voltage spikes on the input supply during short-circuit and overcurrent conditions at the output, the LT1641 features a programmable foldback current limit with an electronic circuit breaker. The current limit is set by placing a Q1 IRF530 RS 0.01 VIN 24V D1 CMPZ 5248B R5 10 5% R1 49.9k 1% R3 59k 1% sense resistor between the VCC and SENSE pins. The current folds back as a function of the output voltage which is sensed at the FB (feedback) pin. If the chip remains in current limit beyond a programmable time limit, the pass transistor latches off. The device may be set to automatically restart after a time-out delay. A variable overcurrent response time provides additional protection under severe fault conditions. The larger the fault voltage across the sense resistor, the faster the gate will be VOUT pulled down, protecting the load. CL C1 R6, 10nF 1k, 5% 8 VCC 1 7 6 SENSE GATE Table 1. Hot Swap Controllers R4 3.57k 1% LT1641 R2 3.4k 1% GND 3 PWRGD GND 5 4 LTC(R)1421 2 FB TIMER Device R7 24k 5% ON Power Good Detection The LT1641 includes a comparator for monitoring the output voltage. The noninverting input (the FB pin) which includes 80mV of hysteresis is compared against an internal 1.233V precision reference. The comparator's output (the PWRGD pin) is an open collector capable of operating from a pull-up as high as 100V. PWRGD can be used to directly enable and disable a power converter module. Table 1 shows the entire line of Hot SwapTM controllers from Linear Technology. PWRGD C2 0.68F #Supplies Supplies Features 2 3V to 12V Controls 3rd Rail to - 12V LTC1422 1 3V to 12V LT1640 1 -10V to - 80V SO-8 LT1641 1 9V to 80V SO-8, Foldback ILIMIT LTC1642 1 3V to 16.5V Fault Protected to 33V LTC1643 4 3.3V, 5V, 12V - 48V in SO-8 Four Supplies, Tiny Package 1641 TA01 Figure 2. 24V Input Voltage Application Micropower Current Sense Amp Operates from 2.5V to 60V with 40V Offset Error--LT1787 The LT1787 is a high resolution current sense amplifier designed for applications such as precise monitoring of the current into or out of a battery (gas gauging) in cellular telephones, portable instruments, computers and wireless telecom devices. The LT1787 has an operating voltage range of 2.5V to 36V so that the device can operate from a single Li-Ion cell and from most other sources. The LT1787HV version can operate on supplies up to 60V, making it useful for high voltage telecommunication and industrial systems. TO LOAD I = 100A 1 2 3 4 FIL+ 8 VS+ 7 LT1787HV VS- VEE RSENSE VS- RSENSE 0.0016 FIL- DNC The LT1787 monitors bidirectional currents via the voltage across an external sense resistor (Figure 1). A current or voltage output from the device depicts the direction and magnitude of the sensed current. The LT1787 allows the use of a selectable sense resistor, the value of which depends on the current to be monitored. This allows the input voltage to be adjusted to a 128mV fullscale range, allowing a maximum dynamic range. The part is generally used at 128mV full scale, although it is specified for a 500mV minimum full scale. The 40V input offset voltage of the LT1787 translates into a 12-bit minimum dynamic range in resolving currents. The LT1787 has a fixed voltage gain of 8 from input to output, set by onboard precision resistors (Figure 2). It is self-powered from the supply that it is monitoring and requires only 60A supply current. Additional features include provisions for input noise filtering (both differential and common mode) and a PSRR of greater than 120dB. The device is available in both 8-lead SO and MSOP packages. - 60V RG1A 1.25k RG2A 1.25k RG1B 1.25k RG2B 1.25k VOUT = (8 * VSENSE) + VREF OUTPUT STEP = 13mV/Amp FIL+ R1 15k C1 1F 5V - + A1 VOUT 5 C2 0.1F VS+ FIL VBIAS 6 ROUT 20k ISENSE VREF VCC CS +IN LTC1286 CLK -IN D GND OUT LT1634-1.25 IOUT TO P Q1 Q2 VBIAS ROUT 20k VOUT 1787 TA01 VEE 1:1 MIRROR 1787 F 01 Figure 1. 12-Bit Dynamic Resolution Bidirectional Output to an ADC Figure 2. LT1787 Functional Diagram Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. 2 Linear Technology Chronicle * November 1999 Application of the Month High Efficiency Linear and Switching Solutions for Splitting a Digital Supply--LT1118 and LTC1504 At low current levels the LT1118 is the optimum solution. The LTC1504 is a synchronous switching regulator that provides as much as 90% efficiency (Figure 2) while sourcing or sinking up to 500mA. It will draw only 56mA from the 5V supply while sourcing 100mA from its 2.5V output. The switching architecture of the LTC1504 requires more external components than the LT1118 (Figure 3) and generates a small amount of output noise D 90 80 VCC 5V IN 0.1F OUT LT1118-2.5 1F NC C F 5V 50 A B 20 10 1 COUT 12.1k 7.5k 220pF 0.01F COUT: AVX TAJC476M016R LEXT: SUMIDA CDRH73-470 (47H: LOW RIPPLE, HIGH EFFICIENCY) SUMIDA CDRH73-220 (22H: FAST TRANSIENT RESPONSE) DN172 F05 10 100 1000 LOAD CURRENT (SINK/SOURCE)(mA) DN172 F02 COMP NC 0 GND + FB SS A: LT1118 SOURCE B: LT1118 SINK C: LTC1504/47H SOURCE D: LTC1504/47H SINK E: LTC1504/22H SOURCE F: LTC1504/22H SINK SPLIT SUPPLY 2.5V 500mA 11.8k LTC1504 GND 40 LEXT SW VCC 4.7F CERAMIC 60 2.5V VIRTUAL GROUND ZOUT < 0.1 SHDN IMAX SHDN E 70 30 0.6mA (ripple) at its 200kHz switching frequency. With a 47H inductor, switching noise is minimal and the circuit recovers from a 400mA output load step in 30s. A shutdown function drops quiescent current below 10A when the split supply is not required. The LTC1504 is the best solution where efficiency, especially at high current levels, is the overriding concern. (See Design Note 172) 100 EFFICIENCY (%) This note presents two methods of creating a split supply with good transient response and minimal supply current in a 5V-only system. The LT1118 is a linear regulator designed to source or sink current to keep its output in regulation. It draws 600A of quiescent current typically and can source 800mA or sink 400mA, enough to satisfy most analog subsystems. The LT1118 requires only two external components (Figure 1) and has a DC output impedance below 0.1. The LT1118 provides nearly 50% power efficiency over a wide range of load currents (Figure 2). Load transient response is excellent with less than 5s recovery time from a 400mA load step. DN172 F03 Figure 1. LT1118-2.5 Supply Splitter Figure 2. Efficiency Comparison Figure 3. LTC1504 Supply Splitter High Efficiency PolyPhase DC/DC Current Mode Controllers Provide 20A to 200A Using Surface Mount Components--LTC1629/LTC1929 cancellation occurs in both the input and output circuits due to properly phased current pulses. Their multiple phase technique effectively multiplies the fundamental frequency by the number of channels used, Continued on page 4 10 S VIN LTC1629 TG1 ITH S SGND M3 TG2 S BOOST2 SW2 VDIFFOUT S BG2 EAIN INTVCC - + VOS + SENSE2 VOUT 1.6V/40A 0.47F S VOS 0.002 D1 SENSE1 - 16k 16k L1 1H SENSE1 + S 100pF S M2 x2 S BG1 PGND 1000pF S 0.47F SW1 RUN/SS 10k M1 S BOOST1 0.1F VIN 5V TO 28V 10F x4 35V CERAMIC 0.1F S + The LTC1629 and LTC1929 are high power true current mode DC/DC controllers. These dramatically simplify the design of DC/DC converters for powering today's high end microprocessors, large memory arrays and other high power loads. Using a unique PolyPhase switching technique, the LTC1629 can be configured to supply load currents up to 200A with inherent current sharing using readily available surface mount components. This PolyPhase technique allows a significant reduction of input and output ripple currents, resulting in high efficiency, low EMI DC/DC converter designs that require very little PC board space. Unlike traditional switching regulators, the LTC1629 and LTC1929 interleave the clock signals of their two paralleled power stages 180 out of phase. Ripple current M4 x2 D2 L2 1H 0.002 10F + SENSE2 - COUT: T510E108K004AS L1, L2: CEPH149-IROMC COUT 1000F x2 4V 1629 TA01 Figure 1. High Current Dual Phase Step-Down Converter Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. Linear Technology Chronicle * November 1999 3 LTC1629/LTC1929 from page 3 improving transient response while operating each channel at an optimum frequency for efficiency. This allows a dramatic reduction in input and output capacitance requirements and EMI generation while improving overall efficiency. The LTC1929 operates in a 2-phase configuration and can support load currents up to 40A. The LTC1629 adds additional internal clock management circuitry that allows multiple devices to be connected in parallel to support higher currents. Using this technique, the LTC1629 can be used in DC/DC converter circuits incorporating up to twelve phases to provide load currents up to 200A. A wide 4V to 36V input range allows the LTC1629 and LTC1929 to operate from a variety of input sources and OPTI-LOOPTM compensation allows the transient response to be optimized for the specific output capacitors used in each application. The LTC1629 and LTC1929 provide output voltages from 0.8V to 6V. An internal differential amplifier provides true remote sensing of the regulated supply's positive and negative output terminals as required in high current applications. Internal current foldback with a shutdown timer and a soft-latch overvoltage protection feature helps protect the load against harmful voltage spikes and overcurrent conditions. The LTC1629 and LTC1929 are both offered in a 28-lead SSOP package, in commercial and industrial temperature grades. Where previous high power applications required the use of an expensive and bulky DC/DC converter module, the LTC1629 and LTC1929 offer a smaller and more efficient alternative that can be easily integrated into even the most space-constrained system. A 10-Bit Voltage Output Micropower DAC in a Tiny SOT-23 Package-- LTC1663 SMBus and I2CTM, allowing multiple devices to drive and monitor the bus without contention. In the MS8 package, eight userselectable addresses allow up to eight LTC1663s to be placed on the same bus. Its ultralow power consumption and small size make the LTC1663 ideal for portable, battery-powered applications where supply current directly affects the operation time and board space is at a premium. The LTC1663 allows the user to select either an internal 1.25V bandgap reference or the positive supply as the DAC's reference voltage. Selecting the internal reference will set the full-scale output voltage to 0V-2.5V. Selecting VCC as the reference extends the full-scale output to the positive supply voltage, adding extra flexibility for ratiometric applications and maximizing the output voltage range. The LTC1663 includes a rail-to-rail output buffer, eliminating the need for external op amps. A DNL of 0.75LSB (max) guarantees true 10-bit monotonic performance over the full temperature range, critical in control loop applications. A power-on reset function ensures that the DAC output is at 0V when power is initially applied and all internal registers are cleared. The LTC1663 is available in MS8 and 5-lead SOT-23 packages. The LTC1663 is a single, 10-bit, voltage output DAC with true buffered rail-torail output voltage capability, all in a tiny SOT-23 package. Operating from supply voltages between 2.7V and 5.5V, the LTC1663 consumes only 60A of supply current and a mere 10A in shutdown mode. The part also features a simple 2-wire serial interface compatible with 5 VCC 1.25V BANDGAP REFERENCE REFERENCE SELECT 10-BIT DAC LATCH + VOUT 8 - COMMAND LATCH R INPUT LATCH Linear Technology Products Are Distributed By: R 6 AD0 2 AD1 3 AD2 2-WIRE INTERFACE SDA SCL GND 1 4 7 Figure 1. LTC1663 Block Diagram 1663 BD Arrow Electronics Arrow/Zeus Components Digi-Key Gerber Electronics Marshall Industries Wyle Electronics (c) 1999 Linear Technology Corporation/Printed in USA Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. Linear * www.linear-tech.com * For Literature 1-800-4-LINEAR 4 Technology Corporation * 1630 McCarthy Blvd. * Milpitas, CA 95035-7417 * (408) 432-1900 * FAX: (408) 434-0507 Linear Technology Chronicle * Only: November 1999