LM2717-ADJ

LM2717-ADJ_08 NSC | Alldatasheet

Document overview

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Technical content

Features

■ Adjustable buck converter with a 2.2A, 0.16Ω, internal switch (Buck 1) ■ Adjustable buck converter with a 3.2A, 0.16Ω, internal switch (Buck 2) ■ Operating input voltage range of 4V to 20V ■ Input undervoltage protection ■ 300kHz to 600kHz pin adjustable operating frequency ■ Over temperature protection ■ Small 24-Lead TSSOP package

Applications

■ TFT-LCD Displays ■ Handheld Devices ■ Portable Applications ■ Laptop Computers ■ Automotive Applications Typical Application Circuit 20167901 © 2008 National Semiconductor Corporation 201679 www.national.com LM2717-ADJ Dual Step-Down DC/DC Converter

Ordering Information

Order Number Spec Package Type NSC Package Drawing Supplied As LM2717MT-ADJ TSSOP-24 MTC24 61 Units, Rail LM2717MTX-ADJ TSSOP-24 MTC24 2500 Units, Tape and Reel LM2717MT-ADJ NOPB TSSOP-24 MTC24 61 Units, Rail LM2717MTX-ADJ NOPB TSSOP-24 MTC24 2500 Units, Tape and Reel www.national.com 2 LM2717-ADJ

1 PGND Power ground. PGND and AGND pins must be connected together directly at the part. 2 PGND Power ground. PGND and AGND pins must be connected together directly at the part. 3 AGND Analog ground. PGND and AGND pins must be connected together directly at the part. 4 FB1 Buck 1 output voltage feedback input. 5 VC1 Buck 1 compensation network connection. Connected to the output of the voltage error amplifier. 6 VBG Bandgap connection. 7 VC2 Buck 2 compensation network connection. Connected to the output of the voltage error amplifier. 8 FB2 Buck 2 output voltage feedback input. 9 AGND Analog ground. PGND and AGND pins must be connected together directly at the part. 10 AGND Analog ground. PGND and AGND pins must be connected together directly at the part. 11 PGND Power ground. PGND and AGND pins must be connected together directly at the part. 12 PGND Power ground. PGND and AGND pins must be connected together directly at the part. 13 SW2 Buck 2 power switch input. Switch connected between VIN pins and SW2 pin. 14 VIN Analog power input. All VIN pins are internally connected and should be connected together directly at the part. 15 VIN Analog power input. All VIN pins are internally connected and should be connected together directly at the part. 16 CB2 Buck 2 converter bootstrap capacitor connection. 17 SHDN2 Shutdown pin for Buck 2 converter. Active low. 18 SS2 Buck 2 soft start pin. 19 FSLCT Switching frequency select input. Use a resistor to set the frequency anywhere between 300kHz and 600kHz. 20 SS1 Buck 1 soft start pin. 21 SHDN1 Shutdown pin for Buck 1 converter. Active low. 22 CB1 Buck 1 converter bootstrap capacitor connection. 23 VIN Analog power input. All VIN pins are internally connected and should be connected together directly at the part. 24 SW1 Buck 1 power switch input. Switch connected between VIN pins and SW1 pin. 3 www.national.com LM2717-ADJ

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Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN −0.3V to 22V SW1 Voltage −0.3V to 22V SW2 Voltage −0.3V to 22V FB1, FB2 Voltages −0.3V to 7V CB1, CB2 Voltages −0.3V to VIN+7V (VIN=VSW) VC1 Voltage 1.75V ≤ VC1 ≤ 2.25V VC2 Voltage 0.965V ≤ VC2 ≤ 1.565V SHDN1 Voltage −0.3V to 7.5V SHDN2 Voltage −0.3V to 7.5V SS1 Voltage −0.3V to 2.1V SS2 Voltage −0.3V to 2.1V FSLCT Voltage AGND to 5V Maximum Junction Temperature 150°C Power Dissipation(Note 2) Internally Limited Lead Temperature 300°C Vapor Phase (60 sec.) 215°C Infrared (15 sec.) 220°C ESD Susceptibility (Note 3) Human Body Model 2kV Operating Conditions Operating Junction Temperature Range (Note 4) −40°C to +125°C Storage Temperature −65°C to +150°C Supply Voltage 4V to 20V SW1 Voltage 20V SW2 Voltage 20V Switching Frequency 300kHz to 600kHz

Electrical Characteristics

Specifications in standard type face are for TJ = 25°C and those with boldface type apply over the full Operating Temperature Range (TJ = −40°C to +125°C). VIN = 5V, IL = 0A, and FSW = 300kHz unless otherwise specified. Symbol Parameter Conditions Min (Note 4) Typ (Note 5) Max (Note 4) Units IQ Total Quiescent Current (both switchers) Not Switching 2.7 6 mA Switching, switch open 6 12 mA VSHDN = 0V 9 27 µA VBG Bandgap Voltage 1.248 1.230 1.267 1.294 1.299 V %VBG/ΔVIN Bandgap Voltage Line Regulation -0.01 0.01 0.125 %/V VFB1 Buck 1 Feedback Voltage 1.236 1.214 1.258 1.286 1.288 V VFB2 Buck 2 Feedback Voltage 1.236 1.214 1.258 1.286 1.288 V ICL1(Note 6) Buck 1 Switch Current Limit VIN = 8V (Note 7) 2.2 AVIN = 12V, VOUT = 3.3V 1.4 1.65 2.0 ICL2(Note 6) Buck 2 Switch Current Limit VIN = 8V (Note 7) 3.2 AVIN = 12V, VOUT = 5V 2.6 3.05 3.5 IB1 Buck 1 FB Pin Bias Current (Note 8) VIN = 20V 70 400 nA IB2 Buck 2 FB Pin Bias Current (Note 8) VIN = 20V 65 400 nA VIN Input Voltage Range 4 20 V gm1 Buck 1 Error Amp Transconductance ΔI = 20µA 1340 µmho gm2 Buck 2 Error Amp Transconductance ΔI = 20µA 1360 µmho AV1 Buck 1 Error Amp Voltage Gain

134 V/V

AV2 Buck 2 Error Amp Voltage Gain

136 V/V

DMAX Maximum Duty Cycle 89 93 % FSW Switching Frequency RF = 46.4k 240 300 360 kHz RF = 22.6k 480 600 720 kHz 5 www.national.com LM2717-ADJ

Symbol Parameter Conditions Min (Note 4) Typ (Note 5) Max (Note 4) Units ISHDN1 Buck 1 Shutdown Pin Current 0V < VSHDN1 < 7.5V −5 5 µA ISHDN2 Buck 2 Shutdown Pin Current 0V < VSHDN2 < 7.5V −5 5 µA IL1 Buck 1 Switch Leakage Current VIN = 20V 0.01 5 µA IL2 Buck 2 Switch Leakage Current VIN = 20V 0.01 5 µA RDSON1 Buck 1 Switch RDSON (Note 9) ISW = 100mA 160 180 300 mΩ RDSON2 Buck 2 Switch RDSON (Note 9) ISW = 100mA 160 180 300 mΩ ThSHDN1 Buck 1 SHDN Threshold Output High 1.8 1.36 VOutput Low 1.33 0.7 ThSHDN2 Buck 2 SHDN Threshold Output High 1.8 1.36 VOutput Low 1.33 0.7 ISS1 Buck 1 Soft Start Pin Current 4 9 15 µA ISS2 Buck 2 Soft Start Pin Current 4 9 15 µA UVP On Threshold 4 3.8 VOff Threshold 3.6 3.3 θJA Thermal Resistance (Note 10) TSSOP, package only 115 °C/W Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. See the Electrical Characteristics table for the thermal resistance. The maximum allowable power dissipation at any ambient temperature is calculated using: PD (MAX) = (TJ(MAX) − TA)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin. Note 4: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100% tested or guaranteed through statistical analysis. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Note 5: Typical numbers are at 25°C and represent the most likely norm. Note 6: Duty cycle affects current limit due to ramp generator. Note 7: Current limit at 0% duty cycle. See TYPICAL PERFORMANCE section for Switch Current Limit vs. Input Voltage. Note 8: Bias current flows into FB pin. Note 9: Includes the bond wires and package leads, RDSON from VIN pin(s) to SW pin. Note 10: Refer to National's packaging website for more detailed thermal information and mounting techniques for the TSSOP package. www.national.com 6 LM2717-ADJ

Typical Performance Characteristics Shutdown IQ vs. Input Voltage 20167960 Switching IQ vs. Input Voltage (FSW = 300kHz) 20167961 Switching Frequency vs. Input Voltage (FSW = 300kHz) 20167962 Buck 1 RDS(ON) vs. Input Voltage 20167963 Buck 2 RDS(ON) vs. Input Voltage 20167964 Buck 1 Efficiency vs. Load Current (VOUT = 3.3V) 20167965 7 www.national.com LM2717-ADJ

Buck 2 Efficiency vs. Load Current (VOUT = 15V) 20167966 Buck 2 Efficiency vs. Load Current (VOUT = 5V) 20167967 Buck 1 Switch Current Limit vs. Input Voltage 20167968 Buck 2 Switch Current Limit vs. Input Voltage 20167969 Buck 1 Switch Current Limit vs. Temperature (VIN = 12V) 20167912 Buck 2 Switch Current Limit vs. Temperature (VIN = 12V) 20167913 www.national.com 8 LM2717-ADJ

Buck 1 Switch ON Resistance vs. Temperature 20167910 Buck 2 Switch ON Resistance vs. Temperature 20167911 Switching Frequency vs. RF Resistance 20167914 Buck Operation PROTECTION (BOTH REGULATORS) The LM2717-ADJ has dedicated protection circuitry running during normal operation to protect the IC. The Thermal Shut- down circuitry turns off the power devices when the die tem- perature reaches excessive levels. The UVP comparator protects the power devices during supply power startup and shutdown to prevent operation at voltages less than the min- imum input voltage. The OVP comparator is used to prevent the output voltage from rising at no loads allowing full PWM operation over all load conditions. The LM2717-ADJ also fea- tures a shutdown mode for each converter decreasing the supply current to approximately 10µA (both in shutdown mode). CONTINUOUS CONDUCTION MODE The LM2717-ADJ contains current-mode, PWM buck regula- tors. A buck regulator steps the input voltage down to a lower output voltage. In continuous conduction mode (when the in- ductor current never reaches zero at steady state), the buck regulator operates in two cycles. The power switch is con- nected between VIN and SW1 and SW2. In the first cycle of operation the transistor is closed and the diode is reverse biased. Energy is collected in the inductor and the load current is supplied by COUT and the rising current through the inductor. During the second cycle the transistor is open and the diode is forward biased due to the fact that the inductor current can- not instantaneously change direction. The energy stored in the inductor is transferred to the load and output capacitor. The ratio of these two cycles determines the output voltage. The output voltage is defined approximately as: where D is the duty cycle of the switch, D and D ′ will be re- quired for design calculations. The LM2717-ADJ has a minimum switch ON time which cor- responds to a minimum duty cycle of approximately 10% at 600kHz operation and approximately 5% at 300kHz opera- tion. In the case of some high voltage differential applications (low duty cycle operation) this minimum duty cycle may be exceeded causing the feedback pin over-voltage protection to trip as the output voltage rises. This will put the device into a PFM type operation which can cause an unpredictable fre- quency spectrum and may cause the average output voltage to rise slightly. If this is a concern the switching frequency may 9 www.national.com LM2717-ADJ

be lowered and/or a pre-load added to the output to keep the device full PWM operation. Note that the OVP function mon- itors the FB pin so it will not function if the feedback resistor is disconnected from the output. Due to slight differences be- tween the two converters it is recommended that Buck 1 be used for the lower of the two output voltages for best opera- tion. DESIGN PROCEDURE This section presents guidelines for selecting external com- ponents. SETTING THE OUTPUT VOLTAGE The output voltage is set using the feedback pin and a resistor divider connected to the output as shown in Figure 4. The feedback pin voltage (VFB) is 1.258V, so the ratio of the feed- back resistors sets the output voltage according to the follow- ing equation: INPUT CAPACITOR A low ESR aluminum, tantalum, or ceramic capacitor is need- ed between the input pin and power ground. This capacitor prevents large voltage transients from appearing at the input. The capacitor is selected based on the RMS current and volt- age requirements. The RMS current is given by: The RMS current reaches its maximum (I OUT/2) when VIN equals 2V OUT. This value should be calculated for both regulators and added to give a total RMS current rating. For an aluminum or ceramic capacitor, the voltage rating should be at least 25% higher than the maximum input voltage. If a tantalum capacitor is used, the voltage rating required is about twice the maximum input voltage. The tantalum capac- itor should be surge current tested by the manufacturer to prevent being shorted by the inrush current. The minimum capacitor value should be 47µF for lower output load current applications and less dynamic (quickly changing) load condi- tions. For higher output current applications or dynamic load conditions a 68µF to 100µF low ESR capacitor is recom- mended. It is also recommended to put a small ceramic capacitor (0.1µF to 4.7µF) between the input pins and ground to reduce high frequency spikes. INDUCTOR SELECTION The most critical parameter for the inductor in a current mode switcher is the minimum value required for stable operation. To prevent subharmonic oscillations and achieve good phase margin a target minimum value for the inductor is: Where VIN is the minimum input voltage and R DSON is the maximum switch ON resistance. For best stability the inductor should be in the range of 0.5L MIN (absolute minimum) and 2LMIN. Using an inductor with a value less than 0.5L MIN can cause subharmonic oscillations. The inductor should meet this minimum requirement at the peak inductor current ex- pected for the application regardless of what the inductor ripple current and output ripple voltage requirements are. A value larger than 2L MIN is acceptable if the ripple require- ments of the application require it but it may reduce the phase margin and increase the difficulty in compensating the circuit. The most important parameters for the inductor from an ap- plications standpoint are the inductance, peak current and the DC resistance. The inductance is related to the peak-to-peak inductor ripple current, the input and the output voltages (for 300kHz operation): A higher value of ripple current reduces inductance, but in- creases the conductance loss, core loss, and current stress for the inductor and switch devices. It also requires a bigger output capacitor for the same output voltage ripple require- ment. A reasonable value is setting the ripple current to be 30% of the DC output current. Since the ripple current in- creases with the input voltage, the maximum input voltage is always used to determine the inductance. The DC resistance of the inductor is a key parameter for the efficiency. Lower DC resistance is available with a bigger winding area. A good tradeoff between the efficiency and the core size is letting the inductor copper loss equal 2% of the output power. OUTPUT CAPACITOR The selection of C OUT is driven by the maximum allowable output voltage ripple. The output ripple in the constant fre- quency, PWM mode is approximated by: The ESR term usually plays the dominant role in determining the voltage ripple. Low ESR ceramic, aluminum electrolytic, or tantalum capacitors (such as MuRata MLCC, Taiyo Yuden MLCC, Nichicon PL series, Sanyo OS-CON, Sprague 593D, 594D, AVX TPS, and CDE polymer aluminum) is recom- mended. An aluminum electrolytic capacitor is not recom- mended for temperatures below −25°C since its ESR rises dramatically at cold temperatures. Ceramic or tantalum ca- pacitors have much better ESR specifications at cold tem- perature and is preferred for low temperature applications. BOOTSTRAP CAPACITOR A 4.7nF ceramic capacitor or larger is recommended for the bootstrap capacitor. For applications where the input voltage is less than twice the output voltage a larger capacitor is rec- ommended, generally 0.1µF to 1µF to ensure plenty of gate drive for the internal switches and a consistently low RDSON. SOFT-START CAPACITOR (BOTH REGULATORS) The LM2717-ADJ contains circuitry that can be used to limit the inrush current on start-up of the DC/DC switching regula- tors. This inrush current limiting circuitry serves as a soft-start. The external SS pins are used to tailor the soft-start for a specific application. A current (ISS) charges the external soft- start capacitor, CSS. The soft-start time can be estimated as: TSS = CSS*0.6V/ISS When programming the soft-start time use the equation given in the Soft-Start Capacitor section above. The soft-start func- tion is used simply to limit inrush current to the device that www.national.com 10 LM2717-ADJ

Application Information

Some Recommended Inductors (Others May Be Used) Manufacturer Inductor Contact Information Coilcraft DO3316 and DT3316 series www.coilcraft.com 800-3222645 TDK SLF10145 series www.component.tdk.com 847-803-6100 Pulse P0751 and P0762 series www.pulseeng.com Sumida CDRH8D28 and CDRH8D43 series www.sumida.com Some Recommended Input And Output Capacitors (Others May Be Used) Manufacturer Capacitor Contact Information Vishay Sprague 293D, 592D, and 595D series tantalum www.vishay.com Taiyo Yuden High capacitance MLCC ceramic www.t-yuden.com Cornell Dubilier ESRD seriec Polymer Aluminum Electrolytic SPV and AFK series V-chip series www.cde.com MuRata High capacitance MLCC ceramic www.murata.com 20167958 FIGURE 4. 15V, 3.3V Output Application

Physical Dimensions inches (millimeters) unless otherwise noted TSSOP-24 Pin Package (MTC) For Ordering, Refer to Ordering Information Table 15 www.national.com LM2717-ADJ

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