LM25011/11Q/11A/11AQ 42V, 2A Constant On-Time Switching Reg w/Adj Current Limit (Rev. H)
Document overview
- Manufacturer or author: Texas Instruments, Incorporated [SNVS617,H]
- PDF pages: 29
Technical content
Sample & Buy T echnical Documents Tools & Software Support & Community LM25011,LM25011-Q1,LM25011A,LM25011A-Q1 SNVS617H –APRIL 2009–REVISED NOVEMBER 2014 LM25011,LM25011-Q1,LM25011A,LM25011A-Q142-V2-AConstantOn-TimeSwitching RegulatorWithAdjustableCurrentLimit
1 Features 3 Description
The LM25011 constant on-time step-down switching 1• LM25011-Q1 is an Automotive Grade Product that regulator features all the functions needed tois AEC-Q100 Grade 1 Qualified (–40°C to +125°C implement a low-cost, efficient, buck bias regulatorOperating Junction Temperature) capable of supplying up to 2 A of load current. This
- LM25011A Allows Low-Dropout Operation at High high-voltage regulator contains an N-Channel Buck Switching Frequency switch, a startup regulator, current limit detection, and internal ripple control. The constant on-time• Input Operating Voltage Range: 6 V to 42 V regulation principle requires no loop compensation,• Absolute Maximum Input Rating: 45 V results in fast load transient response, and simplifies• Integrated 2-A N-Channel Buck Switch circuit implementation. The operating frequency
- Adjustable Current Limit Allows for Smaller remains constant with line and load. The adjustable valley current limit detection results in a smoothInductor transition from constant voltage to constant current• Adjustable Output Voltage from 2.51 V mode when current limit is reached, without the use• Minimum Ripple Voltage at VOUT of current limit foldback. The PGD output indicates
- Power Good Output the output voltage has increased to within 5% of the expected regulation value. Additional features• Switching Frequency Adjustable to 2 MHz include: Low output ripple, VIN under-voltage lock-• COT Topology Features: out, adjustable soft-start timing, thermal shutdown, – Switching Frequency Remains Nearly gate drive pre-charge, gate drive under-voltage lock- Constant with Load Current and Input Voltage out, and maximum duty cycle limit. Variations The LM25011A has a shorter minimum off-time than – Ultra-Fast Transient Response the LM25011, which allows for higher frequency operation at low input voltages.– No Loop Compensation Required – Stable Operation with Ceramic Output Device Information(1) Capacitors PART NUMBER PACKAGE BODY SIZE (NOM) – Allows for Smaller Output Capacitor and LM25011 / -Q1Current Sense Resistor HVSSOP (10) 3.00 mm × 3.00 mm LM25011A / -Q1
- Adjustable Soft-Start Timing (1) For all available packages, see the orderable addendum at• Thermal Shutdown the end of the data sheet.
- Precision 2% Feedback Reference Typical Application• Package: 10-Pin, HVSSOP
2 Applications
- Automotive Safety
- Infotainment
- Telecommunication
- Front Camera An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM25011,LM25011-Q1,LM25011A,LM25011A-Q1 SNVS617H –APRIL 2009–REVISED NOVEMBER 2014 www.ti.com Table of Contents
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision G (February 2013) to Revision H Page
- Added Pin Configuration and Functions section, Handling Rating table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information Changes from Revision F (February 2013) to Revision G Page
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5 Pin Configurations and Functions
PIN I/O DESCRIPTION APPLICATION INFORMATION NUMBER NAME 1 VIN I Input supply voltage Operating input range is 6 V to 42 V. Transient capability is 45 V. A low ESR capacitor must be placed as close as possible to the VIN and SGND pins.
2 RT I On-time Control An external resistor from VIN to this pin sets the buck switch on-
time and the switching frequency.
3 PGD – Power Good Logic output indicates when the voltage at the FB pin has
increased to above 95% of the internal reference voltage. Hysteresis is provided. An external pull-up resistor to a voltage less than 7 V is required.
4 SS I Soft-Start An internal current source charges an external capacitor to
provide the soft-start function.
5 SGND Signal Ground Ground for all internal circuitry other than the current limit sense
circuit. 6 FB I Feedback Internally connected to the regulation comparator. The regulation level is 2.51 V. 7 CSG – Current Sense Ground Ground connection for the current limit sensing circuit. Connect to ground and to the current sense resistor.
8 CS I Current sense Connect to the current sense resistor and the anode of the free-
wheeling diode. 9 SW O Switching Node Internally connected to the buck switch source. Connect to the external inductor, cathode of the free-wheeling diode, and bootstrap capacitor. 10 BST I Bootstrap capacitor connection of Connect a 0.1-µF capacitor from SW to this pin. The capacitor is the buck switch gate driver. charged during the buck switch off-time via an internal diode. - EP – Exposed Pad Exposed pad on the underside of the package. This pad should be soldered to the PC board ground plane to aid in heat dissipation. Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback 3 Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1
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6 Specifications
6.1 Absolute Maximum Ratings(1)
VIN to SGND (TJ = 25°C) 45 V BST to SGND 52 V SW to SGND (Steady State) –1.5 45 V BST to SW –0.3 7 V CS to CSG –0.3 0.3 V CSG to SGND –0.3 0.3 V PGD to SGND –0.3 7 V SS to SGND –0.3 3 V RT to SGND –0.3 1 V FB to SGND –0.3 7 V For soldering specs, see www.ti.com/packaging. Junction Temperature 150 °C (1) Absolute Maximum Ratings(1) are limits beyond which damage to the device may occur. Recommended Operating Conditions are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics .
6.2 Handling Ratings: LM25011
Tstg Storage temperature range –65 150 °C Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, 2000 all pins(1) V(ESD) Electrostatic discharge V Charged device model (CDM), per JEDEC specification 750 JESD22-C101, all pins(2) (1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. (2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Handling Ratings: LM25011-Q1
Tstg Storage temperature range –65 150 °C Human body model (HBM), per AEC Q100-002(1) 2000 Corner pins (1, 5, 6, 750V(ESD) Electrostatic discharge VCharged device model (CDM), per and 10) AEC Q100-011 Other pins 750 (1) AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
6.4 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)(1) MIN MAX UNIT VIN Voltage 6.0 42 V Junction Temperature –40 125 °C (1) Absolute Maximum Ratings(1) are limits beyond which damage to the device may occur. Recommended Operating Conditions are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics .
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6.5 Thermal Information
HVSSOP (DGQ) THERMAL METRIC(1) UNIT
10 PINS
RθJA Junction-to-ambient thermal resistance 48 RθJC(top) Junction-to-case (top) thermal resistance 54.3 RθJB Junction-to-board thermal resistance 34.2 °C/W ψJT Junction-to-top characterization parameter 4.0 ψJB Junction-to-board characterization parameter 33.9 RθJC(bot) Junction-to-case (bottom) thermal resistance 10 (1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback 5 Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1
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6.6 Electrical Characteristics
Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over –40°C to 125°C junction temperature range unless otherwise stated. Unless otherwise stated, the following conditions apply: VIN = 12 V, RT = 50 kΩ.(1) (2) (3) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT INPUT (VIN PIN) IIN Input operating current Non-switching, FB = 3 V 1200 1600 µA UVLOVIN VIN undervoltage lock-out threshold VIN increasing 4.6 5.3 5.9 V VIN undervoltage lock-out threshold hysteresis 200 mV SWITCH CHARACTERISTICS RDS(ON) Buck Switch RDS(ON) ITEST = 200 mA 0.3 0.6 Ω UVLOGD Gate Drive UVLO BST-SW 2.4 3.4 4.4 V UVLOGD Hysteresis 350 mV Pre-charge switch voltage ITEST = 10 mA into SW pin 1.4 V Pre-charge switch on-time 120 ns SOFT-START PIN VSS Pullup voltage 2.51 V ISS Internal current source 10 µA VSS-SH Shutdown threshold 70 140 mV CURRENT LIMIT VILIM Threshold voltage at CS –146 –130 –115 mV CS bias current FB = 3 V –120 µA CSG bias current FB = 3 V –35 µA ON TIMER, RT PIN tON - 1 On-time VIN = 12 V, RT = 50 kΩ 150 200 250 ns tON - 2 On-time VIN = 32 V, RT = 50 kΩ 75 ns tON - 3 On-time (current limit) LM25011 VIN = 12 V, RT = 50 kΩ 100 ns tON - 3 On-time (current limit) LM25011A VIN = 12 V, RT = 50 kΩ 200 ns tON - 4 On-time VIN = 12 V, RT = 301 kΩ 1020 ns tON - 5 On-time VIN = 9 V, RT = 30.9 kΩ 130 171 215 ns tON - 6 On-time VIN = 12 V, RT = 30.9 kΩ 105 137 170 ns tON - 7 On-time VIN = 16 V, RT = 30.9 kΩ 79 109 142 ns OFF TIMER tOFF Minimum off-time (LM25011) 90 150 208 ns Minimum off-time (LM25011A) 52 75 93 REGULATION COMPARATOR (FB PIN) VREF FB regulation threshold SS pin = steady state 2.46 2.51 2.56 V FB bias current FB = 3 V 100 nA POWER GOOD (PGD PIN) Threshold at FB, with respect to VREF FB increasing 91% 95% Threshold hysteresis 3.3% PGDVOL Low state voltage IPGD = 1 mA, FB = 0 V 125 180 mV PGDLKG Off state leakage VPGD = 7 V, FB = 3 V 0.1 µA THERMAL SHUTDOWN TSD Thermal shutdown Junction temperature increasing 155 °C Thermal shutdown hysteresis 20 °C (1) Current flow out of a pin is indicated as a negative number. (2) All hot and cold limits are specified by correlating the electrical characteristics to process and temperature variations and applying statistical process control. (3) The junction temperature (TJ in °C) is calculated from the ambient temperature (TA in °C) and power dissipation (PD in watts) as follows: TJ = TA + (PD × RθJA ) where RθJA (in °C/W) is the package thermal impedance provided in the Thermal Information section.
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6.7 Typical Characteristics
Figure 1. Efficiency (Circuit of Figure 19) Figure 2. Efficiency at 2 MHz Figure 3. On-Time vs VIN and RT Figure 4. Voltage at the RT Pin Figure 5. Shutdown Current into VIN Figure 6. Operating Current into VIN
Figure 7. PGD Low Voltage vs Sink Current Figure 8. Reference Voltage vs Temperature Figure 9. Current Limit Threshold vs Temperature Figure 10. Operating Current vs Temperature Figure 11. VIN UVLO vs Temperature Figure 12. SS Pin Shutdown Threshold vs Temperature
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Figure 13. On-Time vs Temperature Figure 14. Minimum Off-Time vs Temperature
2.5V REGULATION COMPARATOR LM25011(A) /c50A CURRENT LIMIT COMPARATOR FINISHSTART OFF TIMER THERMAL SHUTDOWN FCIC CONTROL PGD 2.375V 0.8V R PGD CSG Power Good 125 mV UVLO SGND RS -CURRENT LIMIT THRESHOLD 6V to 42V C BYPC IN R T C SS C OUT VOUT R FB2 R FB2 Pre -Chg LM25011,LM25011-Q1,LM25011A,LM25011A-Q1 SNVS617H –APRIL 2009–REVISED NOVEMBER 2014 www.ti.com
7 Detailed Description
7.1 Overview
The LM25011 constant on-time step-down switching regulator features all the functions needed to implement a low-cost, efficient buck bias power converter capable of supplying up to 2.0 A to the load. This high-voltage regulator contains an N-Channel buck switch, is easy to implement, and is available in a 10-pin VSSOP, PowerPAD power enhanced package. The operation of the regulator is based on a constant on-time control principle with the on-time inversely proportional to the input voltage. This feature results in the operating frequency remaining relatively constant with load and input voltage variations. The constant on-time feedback control principle requires no loop compensation resulting in very fast load transient response. The adjustable valley current limit detection results in a smooth transition from constant voltage to constant current when current limit is reached. To aid in controlling excessive switch current due to a possible saturating inductor, the on-time is reduced by approximately 40% when the current limit is detected. The Power Good output (PGD pin) indicates when the output voltage is within 5% of the expected regulation voltage. The LM25011 can be implemented to efficiently step-down higher voltages in non-isolated applications. Additional features include: low output ripple, VIN under-voltage lock-out, adjustable soft-start timing, thermal shutdown, gate drive pre-charge, gate drive under-voltage lock-out, and maximum duty-cycle limit.
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Control Circuit Overview
The LM25011 buck regulator employs a control principle based on a comparator and a one-shot on-timer, with the output voltage feedback (FB) compared to an internal reference (2.51 V). If the FB voltage is below the reference, the internal buck switch is switched on for the one-shot timer period which is a function of the input voltage and the programming resistor (RT). Following the on-time, the switch remains off until the FB voltage falls below the reference, but never less than the minimum off-time forced by the off-time one-shot timer. When the FB pin voltage falls below the reference and the off-time one-shot period expires, the buck switch is then turned on for another on-time one-shot period.
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R T = VOUT - (VIN x FS x 15 ns) FS x 4.1 x 10-11 - 500/c3a tON = (VIN) 4.1 x 10-11 x (RT + 500/c3a) + 15 ns FS =VOUT 2 x L1 x 1.19 x 1021 R L x RT DC = tON tON + tOFF == tON x FS VOUT VIN FS = VOUT (4.1 x 10-11 x (RT + 0.5k)) + (VIN x 15 ns) LM25011,LM25011-Q1,LM25011A,LM25011A-Q1 www.ti.com SNVS617H –APRIL 2009–REVISED NOVEMBER 2014 Feature Description (continued) When in regulation, the LM25011 operates in continuous conduction mode at heavy load currents and discontinuous conduction mode at light load currents. In continuous conduction mode, the inductor current is always greater than zero and the operating frequency remains relatively constant with load and line variations. The minimum load current for continuous conduction mode is one-half of the ripple current amplitude of the inductor. The approximate operating frequency is calculated as follows: (1) The buck switch duty cycle is approximately equal to: (2) When the load current is less than one-half of the ripple current amplitude of the inductor, the circuit operates in discontinuous conduction mode. The off-time is longer than in continuous conduction mode while the inductor current is zero, causing the switching frequency to reduce as the load current is reduced. Conversion efficiency is maintained at light loads because the switching losses are reduced with the reduction in load and frequency. The approximate discontinuous operating frequency can be calculated as follows: (3) where RL = the load resistance, and L1 is the inductor in the circuit. The output voltage is set by the two feedback resistors (RFB1, RFB2 in the Functional Block Diagram ). The regulated output voltage is calculated as follows: VOUT = 2.51 V × (RFB1 + RFB2) / RFB1 (4) Ripple voltage, which is required at the input of the regulation comparator for proper output regulation, is generated internally in the LM25011, and externally when the LM25011A is used. In the LM25011 the ERM (emulated ripple mode) control circuit generates the required internal ripple voltage from the ripple waveform at the CS pin. The LM25011A, which is designed for higher frequency operation, requires additional ripple voltage which must be generated externally and provided to the FB pin. This is described in the Application and Implementation section.
7.3.2 On-Time Timer
The on-time for the LM25011/LM25011A is determined by the RT resistor and the input voltage (VIN), calculated from: (5) The inverse relationship with VIN results in a nearly constant frequency as VIN is varied. To set a specific continuous conduction mode switching frequency (FS), the RT resistor is determined from the following: (6) The on-time must be chosen greater than 90 ns for proper operation. Equation 1, Equation 5, and Equation 6 are valid only during normal operation; that is, the circuit is not in current limit. When the LM25011 operates in current limit, the on-time is reduced by approximately 40% (this feature is not present in LM25011A). This feature reduces the peak inductor current which may be excessively high if the load current and the input voltage are simultaneously high. This feature operates on a cycle-by-cycle basis until the load current is reduced and the Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1
7.3.3 Current Limit
RS reduces to its threshold (VOUT is low due to current limiting). reduced, the inductor current increases until the lower peak of the inductor ripple current exceeds the threshold. Figure 15. Normal and Current Limit Operation
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7.3.4 Ripple Requirements
through RS during the off-time. See Figure 16. Figure 16. CS Pin Waveform where ΔI is the inductor current ripple amplitude, and RS is the current-sense resistor at the CS pin. More ripple can be achieved by decreasing the inductor value. are explained in the External Components section.
7.3.5 N-Channel Buck Switch and Driver
driver circuit works in conjunction with an external bootstrap capacitor (CBST) and an internal high-voltage diode. bootstrap capacitor voltage.
7.3.6 Soft-Start
controlled manner. For proper operation, the soft-start capacitor should be no smaller than 1000 pF.
Figure 17. Startup Sequence
7.3.7 Power Good Output (PGD)
falling threshold for the PGD output to switch low is approximately 3.3% below the rising threshold. PGD Low Voltage vs Sink Current.
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7.3.8 Thermal Shutdown
below 135°C (typical hysteresis = 20°C), normal operation resumes.
7.4 Device Functional Modes
7.4.1 Shutdown Function
the pin allows normal operation to resume. Figure 18. Shutdown Implementation
8 Application and Implementation
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.2 Typical Application
8.2.1 LM25011 Example Circuit
measures approximately 1.62 A at VIN = 8 V, and 1.69 A at VIN = 36 V. Figure 19. Example Circuit
8.2.1.1 Design Requirements
Table 1 shows the design parameters. Table 1. Design Parameters
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L1(min) = tON(min) x (VIN(max) - VOUT ) IOR(max) = 7.85 /c50H R T =5 - (8V x 1MHz x 15 ns) 1MHz x 4.1 x 10-11 - 500/c3a/c03= 118.5 k/c3a tOFF(min) = VIN(min) - VOUT VIN(min) x FS = 375 ns8V - 5V 8V x 1 MHz= tON(min) = VOUT VIN(max) x FS = 139 ns5V 36V x 1 MHz= LM25011,LM25011-Q1,LM25011A,LM25011A-Q1 www.ti.com SNVS617H –APRIL 2009–REVISED NOVEMBER 2014
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 External Components
The procedure for calculating the external components is illustrated with a design example using the LM25011. Referring to the Functional Block Diagram , the circuit is to be configured for the following specifications:
- VOUT = 5 V
- VIN = 8 V to 36 V
- Minimum load current for continuous conduction mode IOUT(min) = 300 mA
- Maximum load current IOUT(max) = 1.5 A
- Switching frequency (FSW) = 1.0 MHz
- Soft-start time = 5 ms RFB2 and RFB1: These resistors set the output voltage, and their ratio is calculated from: RFB2/RFB1 = (VOUT / 2.51 V) – 1 (8) For this example, RFB2/RFB1 = 0.992. RFB1 and RFB2 should be chosen from standard value resistors in the range of 1.0 kΩ to 10 kΩ which satisfy the above ratio. For this example, 4.99 kΩ is chosen for both resistors, providing a 5.02-V output. RT: This resistor sets the on-time and (by default) the switching frequency. First check that the desired frequency does not require an on-time or off-time shorter than the minimum allowed values (90 ns and 150, respectively). The minimum on-time occurs at the maximum input voltage. For this example: (9) The minimum off-time occurs at the minimum input voltage. For this example: (10) Both the on-time and off-time are acceptable because they are significantly greater than the minimum value for each. The RT resistor is calculated from Equation 6 using the minimum input voltage: (11) A standard value 118-kΩ resistor is selected. The minimum on-time calculates to 152 ns at VIN = 36 V, and the maximum on-time calculates to 672 ns at VIN = 8 V. L1: The parameters controlled by the inductor are the inductor current ripple amplitude (IOR), and the ripple voltage amplitude across the current sense resistor RS. The minimum load current is used to determine the maximum allowable ripple to maintain continuous conduction mode (the lower peak does not reach 0 mA). This is not a requirement of the LM25011, but serves as a guideline for selecting L1. For this example, the maximum ripple current should be less than: IOR(max) = 2 × IOUT(min) = 600 mAP-P (12) For applications where the minimum load current is zero, a good starting point for allowable ripple is 20% of the maximum load current. In this case substitute 20% of IOUT(max) for IOUT(min) in Equation 12. The ripple amplitude calculated in Equation 12 is then used in Equation 13: (13) A standard value 10-µH inductor is chosen. Using this inductor value, the maximum ripple current amplitude, which occurs at maximum VIN, calculates to 472 mAP-P, and the peak current is 1736 mA at maximum load current. Ensure the selected inductor is rated for this peak current. The minimum ripple current, which occurs at minimum VIN, calculates to 200 mAP-P. Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback 17 Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1
C IN = IOUT(max) x tON(max) /c27V = 2.02 /c50F1.5A x 672 ns 0.5V= Duty Cycle = D = = = 13.9%VOUT VIN 36V LM25011,LM25011-Q1,LM25011A,LM25011A-Q1 SNVS617H –APRIL 2009–REVISED NOVEMBER 2014 www.ti.com RS: The minimum current limit threshold is calculated at maximum load current using the minimum ripple current calculated above. The current limit threshold is the lower peak of the inductor current waveform when in current limit (see Figure 15). Current limit detection occurs when the voltage across the sense resistor (RS) reaches the current limit threshold. To allow for tolerances, the sense resistor value is calculated using the minimum threshold specification: RS = 115 mV / 1.4 A = 82 mΩ (15) The next smaller standard value, 80 mΩ, is selected. The next step is to ensure that sufficient ripple voltage occurs across RS with this value sense resistor. As mentioned in the Ripple Requirements section, a minimum of 15-mVP-P voltage ripple is required across the RS sense resistor during the off-time to ensure the regulation circuit operates properly. The ripple voltage is the product of the inductor ripple current amplitude and the sense resistor value. In this case, the minimum ripple voltage calculates to: VRIPPLE = ΔI × RS = 200 mA × 0.080 Ω = 16 mV (16) If the ripple voltage had calculated to less than 15 mVP-P, the inductor value would have to be reduced to increase the ripple current amplitude. This would have required a recalculation of ILIM and RS in the above equations. Because the minimum requirement is satisfied in this case, no change is necessary. The nominal current limit threshold calculates to 1.63 A. The minimum and maximum thresholds calculate to 1.44 A and 1.83 A, respectively, using the minimum and maximum limits for the current limit threshold specification. The load current is equal to the threshold current plus one-half of the ripple current. Under normal load conditions, the maximum power dissipation in RS occurs at maximum load current, and at maximum input voltage where the on-time duty cycle is minimum. In this design example, the minimum on-time duty cycle is: (17) At maximum load current, the power dissipation in RS is equal to: When in current limit the maximum power dissipation in RS calculates to Duty cycle is not included in this power calculation because the on-time duty cycle is typically <5% when in current limit. COUT: The output capacitor should typically be no smaller than 3.3 µF, although that is dependent on the frequency and the desired output characteristics. COUT should be a low ESR good-quality ceramic capacitor. Experimentation is usually necessary to determine the minimum value for COUT, as the nature of the load may require a larger value. A load which creates significant transients requires a larger value for COUT than a non- varying load. CIN and CBYP: The purpose of CIN is to supply most of the switch current during the on-time, and limit the voltage ripple at VIN, because it is assumed the voltage source feeding VIN has some amount of source impedance. When the buck switch turns on, the current into VIN suddenly increases to the lower peak of the inductor ripple current, then ramps up to the upper peak, and finally drops to zero at turn-off. The average current during the on- time is the average load current. For a worst case calculation, CIN must supply this average load current during the maximum on-time, without letting the voltage at the VIN pin drop below a minimum operating level of 5.5 V. For this exercise 0.5 V is chosen as the maximum allowed input ripple voltage. Using the maximum load current, the minimum value for CIN is calculated from: (20) where tON is the maximum on-time, and ΔV is the allowable ripple voltage at VIN. The purpose of CBYP is to minimize transients and ringing due to long lead inductance leading to the VIN pin. A low ESR 0.1-µF ceramic chip capacitor is recommended, and CBYP must be located close to the VIN and SGND pins. CBST: The recommended value for CBST is 0.1 µF. A high-quality ceramic capacitor with low ESR is recommended as CBST supplies a surge current to charge the buck switch gate at each turn-on. A low ESR also helps ensure a complete recharge during each off-time.
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transitions at the SW pin may affect the regulator operation due to the reverse recovery transients of the diode. where VF is the forward voltage drop of the diode, and D is the on-time duty cycle.
8.2.1.3 Application Curves
Figure 20. Efficiency (Circuit of Figure 19) Figure 21. Frequency vs VIN (Circuit of Figure 19)
8.2.2 Output Ripple Control
additional components to provide ripple at the FB pin with lower output ripple at VOUT. much ripple as needed to stabilize the switching frequency over the required input voltage.
8.2.2.1 Option A: Lowest Cost Configuration
ripple voltage injected at the FB pin.
Figure 22. Option A – Lowest Cost Ripple Configuration
8.2.2.2 Option B: Intermediate VOUT Ripple Configuration
Figure 23. Option B – Intermediate Ripple Configuration
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8.2.2.3 Option C: Minimum VOUT Ripple Configuration
- The time constant Rr × Cr should be more than 8 to 10 times the switching period to generate a triangular
waveform at the junction of Rr, Cr and Cac.
- The minimum ripple at FB (at minimum VIN) is equal to: VRIPPLE = (VIN(min) – VOUT) × TON(max) / (Rr x Cr).
- The ripple capacitor Cr should much smaller than the ac coupling capacitor Cac. Typically Cac = 100 nF, Cr
= 1 nF, and Rr is chosen to satisfy conditions 1 and 2 above. Figure 24. Option C: Minimum Output Ripple Configuration
9 Power Supply Recommendations
small compared to the module input impedance to maintain the stability of the converter.
10 Layout
10.1 Layout Guidelines
The LM25011 regulation and current limit comparators are very fast, and respond to short-duration noise pulses. connection from CSG to the ground end of CIN should be as short and direct as possible.
10.2 Layout Example
Figure 25. Typical Layout
10.3 Power Dissipation
reduce the junction temperature.
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11 Device and Documentation Support
11.1 Related Links
resources, tools and software, and quick access to sample or buy. Table 2. Related Links
11.2 Trademarks
WEBENCH is a registered trademark of Texas Instruments. All other trademarks are the property of their respective owners.
11.3 Electrostatic Discharge Caution
during storage or handling to prevent electrostatic damage to the MOS gates.
11.4 Glossary
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
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www.ti.com 3-Sep-2014 Addendum-Page 1 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Qty Eco Plan (2) Lead/Ball Finish (6) MSL Peak Temp (3) Op Temp (°C) Device Marking (4/5) Samples LM25011AMY ACTIVE MSOP- PowerPAD DGQ 10 1000 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SN9B LM25011AMYE ACTIVE MSOP- PowerPAD DGQ 10 250 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SN9B LM25011AMYX ACTIVE MSOP- PowerPAD DGQ 10 3500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SN9B LM25011AQ1MY/NOPB ACTIVE MSOP- PowerPAD DGQ 10 1000 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SZZA LM25011AQ1MYX/NOPB ACTIVE MSOP- PowerPAD DGQ 10 3500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SZZA LM25011MY/NOPB ACTIVE MSOP- PowerPAD DGQ 10 1000 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SVUB LM25011MYX/NOPB ACTIVE MSOP- PowerPAD DGQ 10 3500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SVUB LM25011Q1MY/NOPB ACTIVE MSOP- PowerPAD DGQ 10 1000 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SZFB LM25011Q1MYX/NOPB ACTIVE MSOP- PowerPAD DGQ 10 3500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 SZFB (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
www.ti.com 3-Sep-2014 Addendum-Page 2 (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. OTHER QUALIFIED VERSIONS OF LM25011, LM25011-Q1 :
- Catalog: LM25011
- Automotive: LM25011-Q1 NOTE: Qualified Version Definitions:
- Catalog - TI's standard catalog product
- Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects
*All dimensions are nominal Device Package Type Package Drawing Pins SPQ Reel Diameter (mm) Reel Width W1 (mm) (mm) (mm) (mm) (mm) W (mm) Pin1 Quadrant LM25011AMY MSOP- Power PAD LM25011AMYE MSOP- Power PAD LM25011AMYX MSOP- Power PAD LM25011AQ1MY/NOPB MSOP- Power PAD LM25011AQ1MYX/NOPB MSOP- Power PAD LM25011MY/NOPB MSOP- Power PAD LM25011MYX/NOPB MSOP- Power PAD PACKAGE MATERIALS INFORMATION www.ti.com 3-Sep-2014 Pack Materials-Page 1
(mm) Reel Width W1 (mm) (mm) (mm) (mm) (mm) W (mm) Pin1 Quadrant Power PAD LM25011Q1MYX/NOPB MSOP- Power PAD *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM25011AMY MSOP-PowerPAD DGQ 10 1000 213.0 191.0 55.0 LM25011AMYE MSOP-PowerPAD DGQ 10 250 213.0 191.0 55.0 LM25011AMYX MSOP-PowerPAD DGQ 10 3500 367.0 367.0 35.0 LM25011AQ1MY/NOPB MSOP-PowerPAD DGQ 10 1000 213.0 191.0 55.0 LM25011AQ1MYX/NOPB MSOP-PowerPAD DGQ 10 3500 367.0 367.0 35.0 LM25011MY/NOPB MSOP-PowerPAD DGQ 10 1000 213.0 191.0 55.0 LM25011MYX/NOPB MSOP-PowerPAD DGQ 10 3500 367.0 367.0 35.0 LM25011Q1MY/NOPB MSOP-PowerPAD DGQ 10 1000 213.0 191.0 55.0 LM25011Q1MYX/NOPB MSOP-PowerPAD DGQ 10 3500 367.0 367.0 35.0 PACKAGE MATERIALS INFORMATION www.ti.com 3-Sep-2014 Pack Materials-Page 2
www.ti.com MUC10A (Rev A) BOTTOM VIEW
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