LM2787BPX

LM2787 www.ti.com SNVS080F – JULY 2001 – REVISED MAY 2013 LM2787 Low Noise Regulated Switched Capacitor Voltage Inverter in DSBGA Check for Samples: LM2787 FEATURES DESCRIPTION • The LM2787 CMOS Negative Regulated Switched Capacitor Voltage Inverter delivers a very low noise adjustable output for an input voltage in the range of +2.7V to +5.5V. Four low cost capacitors are used in this circuit to provide up to 10mA of output current. The regulated output for the LM2787 is adjustable between −1.5V and −5.2V. The LM2787 operates at 260 kHz (typical) switching frequency to reduce output resistance and voltage ripple. With an operating current of only 400 µA (charge pump power efficiency greater than 90% with most loads) and 0.05 µA typical shutdown current, the LM2787 provides ideal performance for cellular phone power amplifier bias and other low current, low noise negative voltage needs. The device comes in small 8-Bump DSBGA and thin DSBGA packages. 1 2 • • • • Inverts and Regulates the Input Supply Voltage Small 8-Bump DSBGA and Thin DSBGA Packages 91% Typical Charge Pump Power Efficiency at 10mA Low Output Ripple Shutdown Lowers Quiescent Current to 0.05 µA (Typical) APPLICATIONS • • • • • Wireless Communication Systems Cellular Phone Power Amplifier Biasing Interface Power Supplies Handheld Instrumentation Laptop Computers and PDA's Typical Application Circuit and Connection Diagram 8-Bump DSBGA (Top View) 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2001–2013, Texas Instruments Incorporated LM2787 SNVS080F – JULY 2001 – REVISED MAY 2013 www.ti.com PIN DESCRIPTIONS Pin No. Name Function A1 Cap+ B1 VIN C1 VOUT C2 VFB Feedback input. Connect VFB to an external resistor divider between VOUT and a positive adjust voltage VADJ (0≤VADJ≤VIN). DO NOT leave unconnected. C3 SD Active low, logic-level shutdown input. B3 VNEG Negative unregulated output voltage. A3 Cap− Negative terminal for C1. A2 GND Ground. Positive terminal for C1. Positive power supply input. Regulated negative output voltage. These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) Supply Voltage (VIN to GND or GND to OUT) + 5.8V (GND − 0.3V) to (VIN + 0.3V) SD VNEG and VOUT Continuous Output Current VOUT Short-Circuit Duration to GND 10mA (3) 1 sec. Continuous Power Dissipation (TA = 25°C) (4) 600mW TJMAX (4) 150°C θJA (4) 220°C/W Operating Input Voltage Range 2.7V to 5.5V Operating Output Current Range 0mA to 10mA −40°C to 85°C Operating Ambient Temp. Range Operating Junction Temp. Range −40°C to 110°C Storage Temperature −65°C to 150°C Lead Temp. (Soldering, 10 sec.) 300°C ESD Rating (5) (1) (2) (3) (4) (5) 2kV Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device beyond its rated operating conditions. If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications. OUT may be shorted to GND for one second without damage. However, shorting OUT to VIN may damage the device and must be avoided. Also, for temperatures above TA = 85°C, OUT must not be shorted to GND or VIN or device may be damaged. The maximum power dissipation must be de-rated at elevated temperatures and is limited by TJMAX (maximum junction temperature), TA (ambient temperature) and θJA (junction-to-ambient thermal resistance). The maximum power dissipation at any temperature is:PDissMAX = (TJMAX — TA)/θJA up to the value listed in the Absolute Maximum Ratings. Rating is for the human body model, a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin. Electrical Characteristics Limits with standard typeface apply for TJ = 25°C, and limits in boldface type apply over the full temperature range. Unless otherwise specified VIN = 3.6V, C1 = C2 = C3 = 1µF. Symbol (1) 2 Parameter Conditions IQ Supply Current ISD Shutdown Supply Current FSW Switching Frequency (1) VIN = 3.6V ηPOWER Power Efficiency at VNEG IL = 3.6mA IL = 10mA TSTART Start Up time Min Open Circuit, No Load 140 Typ Max Units µA 400 950 0.05 1 µA 260 450 kHz 94 91 120 % 600 µs The output switches operate at one half the oscillator frequency, fOSC = 2fSW. Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated Product Folder Links: LM2787 LM2787 www.ti.com SNVS080F – JULY 2001 – REVISED MAY 2013 Electrical Characteristics (continued) Limits with standard typeface apply for TJ = 25°C, and limits in boldface type apply over the full temperature range. Unless otherwise specified VIN = 3.6V, C1 = C2 = C3 = 1µF. Symbol RNEG VR VFB VOUT (2) (3) (4) Parameter Conditions Output Resistance to VNEG Output Voltage Ripple (3) Min Typ See (2) IL =2.5mA, VOUT = −2.7V IL = 10mA, VOUT = −3.8V (4) Feedback Pin Reference Voltage IL = 2.5mA Adjustable Output Voltage 5.5V ≥ VIN ≥ 2.7V, 2.5mA ≥ IL 5.5V ≥ VIN ≥ 3.0V, 10mA ≥ IL ≥ 0mA Load Regulation 0 to 10mA, VOUT = − 2.4V Line Regulation 5.5V ≥ VIN ≥ 2.7V, IL = 2.5mA VIH Shutdown Pin Input Voltage High 5.5V ≥ VIN ≥ 2.7V VIL Shutdown Pin Input Voltage Low 5.5V ≥ VIN ≥ 2.7V −1.25 Max Units 30 Ω 1 mV −1.20 −1.15 V − (VIN −0.3V) − (VIN −1.2V) V 5 mV/mA 1 mV/V 2.4 V 0.8 V Current drawn from VNEG pin decreases power efficiency and will increase output voltage ripple. In the test circuit, capacitors C1, C2, and C3 are 1µF, 0.30Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, increase output voltage ripple, and reduce efficiency. The feedback resistors R1 and R2 are 200kΩ resistors. Figure 1. Standard Application Circuit Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated Product Folder Links: LM2787 3 LM2787 SNVS080F – JULY 2001 – REVISED MAY 2013 www.ti.com Typical Performance Characteristics Unless otherwise specified, TA = 25°C, VOUT = −2.5V. 4 Output Voltage vs. Output Current Output Voltage vs. Input Voltage Figure 2. Figure 3. Maximum VNEG Current vs. Input Voltage No Load Supply Current vs. Input Voltage Figure 4. Figure 5. Switching Frequency vs. Input Voltage VFB vs. Temperature Figure 6. Figure 7. Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated Product Folder Links: LM2787 LM2787 www.ti.com SNVS080F – JULY 2001 – REVISED MAY 2013 Typical Performance Characteristics (continued) Unless otherwise specified, TA = 25°C, VOUT = −2.5V. Start-up Time vs. Input Voltage Start-up from Shutdown (no load) Figure 8. Figure 9. Output Ripple Output Noise Spectrum Figure 10. Figure 11. Line Transient Response Load Transient Response Figure 12. Figure 13. Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated Product Folder Links: LM2787 5 LM2787 SNVS080F – JULY 2001 – REVISED MAY 2013 www.ti.com FUNCTIONAL BLOCK DIAGRAM Figure 14. Functional Block Diagram Device Description The LM2787 is an inverting, regulated charge-pump power converter. It features low noise, small physical size, and is simple to use. It is an ideal solution for biasing GaAsFET devices such as power amplifier modules found in portable devices and cellular phones. A switched capacitor charge-pump circuit is used to invert the input voltage VIN to its corresponding negative value which is seen at VNEG. This voltage is regulated by a low dropout linear regulator at VOUT (Figure 14). The output voltage can be regulated anywhere from −1.5V to −5.2V and is determined by a pair of feedback resistors (see Setting the Output Voltage). The PSRR of the linear regulator reduces the output voltage ripple produced by the charge-pump inverter at the output VOUT. The regulator also attenuates noise from the incoming supply due to its high PSRR. Shutdown The LM2787 features a logic-level shutdown feature. The function is active-low and will reduce the supply current to 0.05µA (typical) when engaged. When shutdown is active VOUT and VNEG are switched to ground. APPLICATION INFORMATION Setting the Output Voltage The output voltage on the LM2787 is set by using a resistor divider between the output, the feedback pin, and an arbitrary voltage VADJ (Figure 14). VADJ can range from GND to any positive voltage up to VIN. VADJ is usually chosen to be GND and should not be connected to a different voltage unless it is well regulated so the output will stay constant. The feedback pin is held at a constant voltage VFB which equals −1.2V. The output voltage can be selected using the equation: (1) The current into the feedback pin IFB is in the range of 10nA to 100nA. Therefore using a value of 500kΩ or smaller for R1 should make this current of little concern when setting the output voltage. For best accuracy, use resistors with 1% or better tolerance. Capacitor Selection Selecting the right capacitors for your circuit is important. The capacitors affect the output resistance of the charge-pump, the output voltage ripple, and the overall dropout voltage (VIN-|VOUT|) of the circuit. The output resistance of the charge-pump inverter is: 6 Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated Product Folder Links: LM2787 LM2787 www.ti.com SNVS080F – JULY 2001 – REVISED MAY 2013 (2) The switching frequency is fixed at 260kHz and RSW (the combined resistance of the internal switches) is typically 10Ω. It is clear from this equation that low ESR capacitors are desirable and that larger values of C1 will further reduce the output resistance. The output resistance of the entire circuit (in dropout) is: ROUT = RNEG + Rregulator (3) Rregulator (the output impedance of the linear regulator) is approximately 10Ω. When the circuit is in regulation, the overall output resistance is equal to the linear regulator load regulation (5mV/mA). The dropout voltage is therefore affected by the capacitors used since it is simply defined as IOUT*ROUT. A larger value of capacitor and lower ESR for C2 will lower the output voltage ripple of the charge-pump. This ripple will then be subject to the PSRR of the linear regulator and reduced at VOUT. In summation, larger value capacitors with lower ESR will give the lowest output noise and ripple. C1, C2, and C3 should be 1.0µF minimum with less than 0.3Ω ESR. Larger values may be used for any or all capacitors. All capacitors should be either ceramic, surface-mount chip tantalum, or polymer electrolytic. Output Noise and Ripple Low output noise and output voltage ripple are two of the attractive features of the LM2787. Because they are small, the noise and ripple can be hard to measure accurately. Ground loop error between the circuit and the oscilloscope caused by the switching of the charge-pump produces ground currents in the probe wires. This causes sharp voltage spikes on the oscilloscope waveform. To reduce this error, measure the output directly at the output capacitor (C3) and use the shortest wires possible. Also, do not use the ground lead on the probe. Take the tip cover off of the probe and touch the grounding ring of the probe directly to the output ground. This should give the most accurate reading of the actual output waveform. DSBGA Mounting The DSBGA package requires specific mounting techniques which are detailed in Application Note AN1112. Referring to the section Surface Mount Technology (SMT) Assembly Considerations, it should be noted that the pad style which must be used with the 8-pin package is the NSMD (non-solder mask defined) type. For best results during assembly, alignment ordinals on the PC board may be used to facilitate placement of the DSBGA device. DSBGA Light Sensitivity Exposing the DSBGA device to direct sunlight may cause misoperation of the device. Light sources such as Halogen lamps can also affect electrical performance if brought near the device. The wavelengths which have the most detrimental effect are reds and infra-reds. The fluorescent lighting used inside of most buildings has very little effect on performance. Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated Product Folder Links: LM2787 7 LM2787 SNVS080F – JULY 2001 – REVISED MAY 2013 www.ti.com REVISION HISTORY Changes from Revision E (May 2013) to Revision F • 8 Page Changed layout of National Data Sheet to TI format ............................................................................................................ 7 Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated Product Folder Links: LM2787 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. 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