LX1734 MICROSEMI | Alldatasheet
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Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ®
DESCRIPTION
The LX1734 is an inverting DC/DC current-mode controller. With a 750mA integrated switch, the LX1734 can generate large output currents in a small footprint. The LX1734 minimizes external com- ponent size and cost by implementing a high switching frequency of 1.0MHz, while generating -5V at 250mA. When configured in the dual inductor inverting topology very low output voltage ripple approaching 1mV P-P can be achieved when used in conjunction with ceramic output capacitors. The dual inductor can be implemented as a coupled or separate cores. Fixed frequency operation ensures a clean output free from low frequency noise typically present with charge pump solutions. The low impedance outpu t remains within 1% of nominal during large load steps. The 18V switch allows high voltage outputs to be generated. The LX1734 is available in the space saving 6-lead 3x3 Jedec MO-229 package, which has the same footprin t and lead spacing as the SOT-23A. A complete inverter function utilizes less than 0.32 inches of PCB space. IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com KEY FEATURES Fixed Frequency 1.0MHz Operation Very Low Noise: 1mV P-P Output Ripple Possible With Cuk Topology Stable Operation With Ceramic or Tantalum Capacitors -5V at 250mA from 5V Input Uses Small Surface Mount L/C Components Wide Input Range: 4.2V to 8V Low VCESAT Switch: 600mV at 600mA 6-Lead 3x3mm JEDEC MLPM Package Functionally Compatible with LT1611 or LT1931 APPLICATIONS/BENEFITS Disk Drive MR Head Bias Digital Camera CCD Bias LCD Bias GaAs FET Bias Local -5V or -12V Supplies PRODUCT HIGHLIGHT 10µF VIN = 5V LX1734 VIN SW L1A 22µH GND NFB 1µF 10k 29.4k L1B 22µH 22µF VOUT = -5V @ 150mA 1000pF Note: L1A and L1B are shown as coupled. Individual inductors can also be used. C1, C2, C3 are ceramic capacitors SD Figure 1 PACKAGE ORDER INFO LM Plastic MLPL 6-Pin TA (°C) RoHS Compliant / Pb-free Transition DC: 0452 0 to 85 LX1734CLM Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1734CLM-TR) LLXX11773344
Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ® ABSOLUTE MAXIMUM RATINGS Peak Package Solder Reflow Temperature 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. THERMAL DATA LM Plastic LM 6-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJC 8°C/W Junction Temperature Calculation: TJ = TA + (PD x θJC). The θJC numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. PACKAGE PIN OUT SW GND NFB SD VIN N/C* LM PACKAGE (Top View) * Not Internally Connected. ** Package heatsink should be connected to ground or left floating. RoHS / Pb-free 100% Matte Tin Lead Finish FUNCTIONAL PIN DESCRIPTION NAME D ESCRIPTION SW Power Switch Pin GND Common ground reference NFB Feedback Pin - Connect to a resistive divider in order to set the output voltage. Feedback threshold is -1.235V. Given the typical NFB bias current (INFB) of 4µA flows out of the pin, the suggested value for R2 is 10K. Given R2, set R1 according to: ()NFBIR VOUT R 235.1 235.1 VIN Input Supply – Input pin must be locally bypassed. SD Shutdown, Connected to >2V, device is active. PPAACCKKAAGGEE DDAATTAA
Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ®
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 85°C and the following test conditions: VIN = 5V LX1734 Parameter Symbol Test Conditions Min Typ Max Units Minimum Operating Voltage VIN 4.25 V V IN Under Voltage Lockout UVLO V IN rising, regulator remains off 3.2 4.25 V Reference Voltage VNFB -1.205 -1.235 -1.255 V Reference Voltage Line Regulation 4.5V < VIN < 5.5V, TAMB > 25°C 18 mV NFB Pin Bias Current INFB -4 -8 µA Quiescent Current IQ (Regulator Not Switching, VNFB = -2V) 9 12 mA Quiescent Current ISHDN SDV < 0.28V 300 µA Switching Frequency I OUT = 5mA to 250mA 0.8 1.4 MHz Maximum Duty Cycle 82 % Switch VCESAT I SW = 600mA 650 800 mV Switch Leakage Current V SW = 10V 0.02 1 µA Switch Circuit Current Limit Duty Cycle < 50% 700 mA High VSDH Device Active 2 V Low VSDL Device Disabled 0.8 V SDV = 0.28V -5 0.4 1.0 µA Shutdown Input Voltage Bias Current ISD SDV = 5V 30 50 µA BLOCK DIAGRAM VIN NFB 100k 40pF Q Q SET CLRS R 0.1Ω Σ SW GND Ramp Generator 1.1MHz Oscillator R1 (External) R2 (External) CPL VOUT UVLO SD BIAS Figure 2 – Simplified Block Diagram EELLEECCTTRRIICCAALLSS
Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ® CONDITIONS: VIN @ 5V, VOUT @ -5V, CIN=COUT=10uF Ceramic, L1=L2=10uH STEP LOAD RESPONSE 0 – 100mA STEP LOAD RESPONSE 0 – 250mA POWER ON RESPONSE, IOUT @ 200mA OUTPUT VOLTAGE RIPPLE, IOUT @ 10mA and 150 mA LX1734 TEMPERATURE STABILITY IL = 132mA -5.2 -5.16 -5.12 -5.08 -5.04 -4.96 -4.92 -4.88 -4.84 -15 0 15 30 45 60 75 90 105 120 800 830 860 890 920 950 980 1010 1040 1070 Vout, Volts FREQ, Khz TEMP, °C WWAAVVEEFFOORRMMSS VOUT VIN Inductor, 2A/div VOUT ISTEP LOAD VOUT ISTEP LOAD IOUT = 10Ma IOUT = 150mA
Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ® THEORY OF OPERATION The LX1734 is a fixed frequency current mode controller designed to develop a negative output voltage from a positive input voltage. The switching transi stor and current sense resistor are integrated into the part. The PWM functions in a peak current regulation mode using the amplif ied error signal to determine the peak switch current each cycle. Slope compensation is added to provide stable operation at high duty cycles. A current limit detector overrides the regulation loop and prevents the switch current from exceeding the over current threshold level. The bandgap control circuit keeps Q1 biased on and produces a reference current (I REF) that produces a voltage drop across the internal resistance that has a positive temperature coefficient. When this resistor voltage drop is added to the negative temperature coefficient of the base-emitter voltage drop of Q1, the result is a temperature compensated reference voltage (V REF) at the NFB pin. The summing node from the external feedback network is connected directly to NFB pin, which is relatively high impedance (typically 150k). The feedback loop minimizes the error current, (IERROR) which effectively regulates the voltage at the NFB pin. As with a conventional error amplifie r, the error signal is proportional to the difference between the temperature compensated reference voltage (V REF) and the summing node voltage. A slight correction factor is necessary to account for the added summing node voltage due to the reference current (I REF, typically 4µADC) flowing through the Thevenin equivalent summing node external resistance. APPLICATION NOTE The LX1734 can be used in severa l topologies that generate a negative output voltage from a positive input voltage. The LX1734 can be used in a dual induc tor converter with coupled or uncoupled inductors (see Figure 1); this topology is required if the absolute value of the output voltage is less than or equal to the input voltage but can also be us ed for higher voltage outputs. The following components or their equivalents can be used to implement the converter in Figure 1, which produces a –5V output at 150mA from a +5V input. The reference design has an efficiency of greater than 72% a nd an input ripple voltage of less than 6mVP-P and an output ripple voltage of less than 300µVP-P. Ref Description Part Number Manufacturer C1 Ceramic, 4.7uF, 6.3V (0805) JMK212BJ475MG Taiyo Yuden C2 Ceramic, 1uF, 16V (0805) GRM40X7R105M16 Murata C3 Ceramic, 22uF, 6.3V (1210) JMK325BJ226MM Taiyo Yuden C4 Ceramic, 470pF, 50V (0402) GRM36X7R471K050 Murata D1 Diode, 0.5A, 30V UPS530 Microsemi L1 Inductor, Coupled, 22uH CLS62-220NC Sumida Table 1 - Part List for Figure 1 (All Parts Are Surface Mount). Separate inductors (not on a common core) can be used in place of the coupled inductor (L1) of Figure 1. In this case the only component that changes in the parts list is L1, which now would be two separate inductors (L1, formerly L1A, and L2, formerly L1B). With the separate indu ctors the peak-to-peak voltage ripple on the input the output were less the 2mV P-P and less than 500µVP-P, respectively. Table 2 - Part List For Alternative Inductors Ref. Designator Description Part Number Manufacturer L1, L2 Inductor, 47uH, (1812) LQH4C470K04M00 Murata Inductor Selection When the LX1734 is used in a du al inductor converter with coupled inductors, a parallel winding inductor value of 22µH works well for a 5V input and a -5V output at 150mA. The inductor value can be scaled to the particular set of operating conditions based on the input voltage, output voltage, and output current. The new value of coupled inductor parallel inductance can be calculated using the following equation: ⎛×⎟ ⎛×= OUTOUT IN NEW V I mA150 VµH22L The inductor value should be rounded to the nearest available value. The parallel saturation current rating of a coupled inductor should be sized to carry the summation of the peak input and peak output inductor currents. When the LX1734 is used in a dual inductor converter with two separate (uncoupled) inductors or when using the boost converter with an inverting charge pump output configuration, the inductance value for each inductor should be about twice the value recommended for a coupled inductor. The peak current in the inductor is the DC current plus ½ of the peak-to-peak ripple current. The saturation current rating of the inductors should be sized to carry the peak inductor current. The peak-to-peak ripple current can be calculated based on the inductor value, the terminal voltage (input or output), and the duty cycle. The DC inductor current is the same as the DC output current on the output inductor. The DC input current includes the power for the LX1734, but is still a good approximation for the DC inductor current for higher power applications. For simplicity, the calculations below ignore the voltage drops of the switch and diode. The duty cycle, D, for the dual inductor topology (assuming continuous inductor current mode operation) is approximately: AAPPPPLLIICCAATTIIOONN
Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ® APPLICATION NOTE (CONTINUED) () 0 V where OUT <−= INOUT OUT VV VD For example, the duty cycle for +5V = VIN and –3.3V = VOUT is 40%. The duty cycle for the Inverting Charge Pump Output topology (assuming continuous inductor c urrent mode operation) is approximately:
0 V where OUT <⎟⎟
⎛+= OUT IN V V1D For example, the duty cycle for +5V = VIN and –12V = VOUT is 58%. The peak-to-peak ripple current in the input inductor is approximately: frequency) switching (the 1.0MHz Fsw where FswL DVI IN IN RIPPLEpp For example, with a +5V input and a-12V output in an Inverting Charge Pump Output topology with a 47µH inductor, the peak-to- peak input ripple is 52mA. In the dual inductor topology with separate inductors, the peak- to-peak ripple current in the output inductor is approximately: ( )[ ] () FswL D1VI OUT OUT ppRIPPLE −×−= For example, with a +5V input and a -3.3V output in a dual inductor topology with a 47µH output inductor, the peak-to-peak output ripple is 35mA. There are many inductor models from many different manufacturers that work well with the LX1734. Some sources are listed in Table 5. Ferrite core inductors are recommended to reduce core losses due to the high operating frequency of the LX7134. Using inductors with low DC resistance will further reduce efficiency losses. Vendor Phone URL Part Comments CLS62-22022 22µH Coupled Sumida (847) 956-0666 www.sumida.com CD43-470 47µH Murata (404) 436-1300 www.murata.com LQH3C-220 22µH, 2mm Height Coiltronics (407) 241-7876 www.coiltronics.com CTX20-1 20µH, Coupled, Low DCR Table 5 – List of Inductor Vendors Capacitor Selection To minimize ripple voltage, only capacitors with low series resistance (ESR) are recommended. Mutli-layer ceramic capacitors with X5R or X7R dielectric are an excellent choice featuring small size, very low ESR, and a temperature stable dielectric. The level shifting capacitor, C2 (of Figure 1), should have a value of 1µF and a voltage difference between the input and output voltages. The input and output capacitors (C1 an d C2, respectively) should have values in the range of 1µF or larger. If the inductor ripple current is known, the ripple voltage can be estimated by the following equation: ( ) () VC2 LIV PPRIPPLE PP(RIPPLE) Since ripple voltage is inversely proportional to the capacitor value, larger value ceramic capacitors will result in lower ripple voltages. When using a ceramic capacitor for the output capacitor, it is recommended that a phase lead netw ork be inserted in the feedback loop to improve the transient resp onse. This can be accomplished by placing a capacitor in parallel w ith resistor R1 (see Figure 1). The corner frequency for the phase lead zero is between 20KHz and 60KHz. C4 can be calculated using the following equation: () 4C1Rπ2 ××=zf Electrolytic capacitors such as solid tantalum or OS-CON types can also be used with consideration for the ESR. Since ESR adds to the capacitor reactive impedance, ESR will increase the ripple voltage. The electrolytic output capacitor impedance has a built in zero, so adding C4 is usually not requir ed when using an electrolytic capacitor. Diode Selection A Schottky diode is recommended for use with the LX1734. The Microsemi UPS530 (30V @ 0.5A) or Microsemi UPS5817 (20V @ 1A) are good choices. Layout Considerations In operation, current is transferre d between the LX1734 and D1 so to minimize ground noise it is recommended that the D1 cathode be connected directly to the ground pin pad for the LX1734 (refer to figure 1). When laying out the converter, to minimize EMI, it is important to minimize the area enclosed within the main current loops. It is also important to minimize the length of etch connecting to pin 3 (NFB) and to minimize the total trace area on both sides of C2. A ceramic bypass capacitor shou ld be connected between pin 5 (VIN) and pin 2 (GND) and located in close proximity to the LX1734. AAPPPPLLIICCAATTIIOONN
Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ® PACKAGE DIMENSIONS LM 6-Pin Plastic Exposed Pad JEDEC MO-229 Reference e AA2 TOP VIEW SIDE VIEW BOTTOM VIEW L b θ E D .08 A1A3 MILLIMETERS INCHES Dim MIN MAX MIN MAX A 0.80 1.05 0.031 0.041 A1 * 0.05 0.002 A2 0.65 0.75 0.025 0.295 A3 0.15 0.25 0.006 0.010 b 0.33 0.45 0.012 0.017 D 2.90 3.10 0.114 0.122 E 2.90 3.10 0.114 0.122 e 0.95 BSC 0.037 BSC D2 1.78 2.34 0.070 0.092 E2 1.01 1.57 0.039 0.061 L 0.20 0.45 0.007 0.017 K 0.20 * 0.007 * θ 0° 12° 0° 12° 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. MMEECCHHAANNIICCAALL
Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8Copyright © 2002 Rev. 3.0a, 2005-03-14 WWW.Microsemi .COM LX1734 1.0MHz Inverting DC/DC Converter TM ® NOTES PRODUCTION DATA – Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time. NNOOTTEESS