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LM25085

PGATE

ISEN

GND

VCC

ADJ

4.5V to 42V

Input

GND

SHUTDOWN

VCC

ADJ

Cff

OUT

FB2

FB1

OUT

GND

VIN

LM25085, LM25085-Q1

www.ti.com

SNVS593H –OCTOBER 2008–REVISED MARCH 2013

LM25085, LM25085-Q1 42V Constant On-Time PFET Buck Switching Controller

Check for Samples: LM25085, LM25085-Q1

FEATURES

PACKAGE

• LM25085-Q1 is an Automotive Grade product

• HVSSOP-8

that is AEC-Q100 Grade 1 Qualified (-40°C to

• VSSOP-8

125°C Operating Junction Temperature)

• WSON-8 (3mm x 3mm)

• Wide 4.5V to 42V Input Voltage Range

• Adjustable Current Limit Using R

DS(ON)

or a DESCRIPTION

Current Sense Resistor

The LM25085 is a high efficiency PFET switching

regulator controller that can be used to quickly and

• Programmable Switching Frequency to 1MHz

easily develop a small, efficient buck regulator for a

• No Loop Compensation Required

wide range of applications. This high voltage

• Ultra-Fast Transient Response

controller contains a PFET gate driver and a high

voltage bias regulator which operates over a wide

• Nearly Constant Operating Frequency with

4.5V to 42V input range. The constant on-time

Line and Load Variations

regulation principle requires no loop compensation,

• Adjustable Output Voltage from 1.25V

simplifies circuit implementation, and results in ultra-

• Precision ±2% Feedback Reference

fast load transient response. The operating frequency

remains nearly constant with line and load variations

• Capable of 100% Duty Cycle Operation

due to the inverse relationship between the input

• Internal Soft-Start Timer

voltage and the on-time. The PFET architecture

• Integrated High Voltage Bias Regulator

allows 100% duty cycle operation for a low dropout

voltage. Either the R

DS(ON)

of the PFET or an external

• Thermal Shutdown

sense resistor can be used to sense current for over-

current detection.

Typical Application, Basic Step Down Controller

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.

2All 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.

Summary of content (30 pages)

PAGE 1
LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 LM25085, LM25085-Q1 42V Constant On-Time PFET Buck Switching Controller Check for Samples: LM25085, LM25085-Q1 FEATURES PACKAGE • • • • 1 2 • • • • • • • • • • • • LM25085-Q1 is an Automotive Grade product that is AEC-Q100 Grade 1 Qualified (-40°C to 125°C Operating Junction Temperature) Wide 4.
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com Connection Diagram Exposed Pad on Bottom Connect to Ground 8 VIN 2 7 VCC FB 3 6 PGATE GND 4 5 ISEN 1 ADJ RT ADJ 1 8 VIN RT 2 7 VCC FB 3 6 PGATE GND 4 5 ISEN Exposed Pad on Bottom Connect to Ground Figure 1. Top View 8-Lead HVSSOP-PowerPAD See Package Number DGN0008A Figure 3.
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LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 Absolute Maximum Ratings (1) (2) VIN to GND -0.3V to 45V ISEN to GND -0.3V to VIN + 0.3V ADJ to GND -0.3V to VIN + 0.3V RT, FB to GND -0.3V to 7V VIN to VCC, VIN to PGATE -0.3V to 10V ESD Rating (3) Human Body Model 2kV Storage Temperature Range (1) (2) (3) -65°C to +150°C Absolute Maximum Ratings are limits beyond which damage to the device may occur.
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com Electrical Characteristics (continued) Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only.
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LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 Typical Performance Characteristics Unless otherwise specified the following conditions apply: TJ = 25°C, VIN = 24V. Efficiency (Circuit of Figure 28) Input Operating Current vs. VIN Figure 4. Figure 5. Shutdown Current vs. VIN VCC vs. VIN Figure 6. Figure 7. VCC vs. ICC On-Time vs. RT and VIN Figure 8. Figure 9.
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified the following conditions apply: TJ = 25°C, VIN = 24V. 6 Off-Time vs. VIN and VFB Voltage at the RT Pin Figure 10. Figure 11. ADJ Pin Current vs. VIN Input Operating Current vs. Temperature Figure 12. Figure 13. Shutdown Current vs. Temperature VCC vs. Temperature Figure 14. Figure 15.
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LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified the following conditions apply: TJ = 25°C, VIN = 24V. On-Time vs. Temperature Minimum On-Time vs. Temperature Figure 16. Figure 17. Off-Time vs. Temperature Current Limit Comparator Offset vs. Temperature Figure 18. Figure 19. ADJ Pin Current vs. Temperature PGATE Driver Output Resistance vs. Temperature Figure 20. Figure 21.
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified the following conditions apply: TJ = 25°C, VIN = 24V. Feedback Reference Voltage vs. Temperature Soft-Start Time vs. Temperature Figure 22. Figure 23. RT Pin Shutdown Threshold vs. Temperature Figure 24.
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LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 Block Diagram 4.5V to 42V Input VIN Negative Bias Regulator VIN CIN GND 7.7V CBYP LM25085 + - 0.73V RT + CVCC CADJ Thermal Shutdown RT + VCC VIN RADJ VCC UVLO ON Time One-Shot Gate Driver RSEN PGATE Q1 SHUTDOWN VCC 1.25V Soft-Start Gate Driver Control Logic L1 ADJ COUT 40 PA + QS - R REGULATION COMPARATOR 1.
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com The LM25085 is available in both an 8 pin HVSSOP-PowerPAD package and an 8 pin WSON package with an exposed pad to aid in heat dissipation. An 8 pin VSSOP package without an exposed pad is also available. REGULATION CONTROL CIRCUIT The LM25085 buck DC-DC controller employs a control scheme based on a comparator and a one-shot ontimer, with the output voltage feedback compared to an internal reference voltage (1.25V).
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LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 To set a specific continuous conduction mode switching frequency (FS), the RT resistor is determined from the following: where • RT is in kΩ (5) A simplified version of Equation 5 at VIN = 12V, and tD = 100ns, is: RT = VOUT x 6 x 106 - 8.6 FS For VIN = 42V and tD = 100ns, the simplified equation is: SHUTDOWN The LM25085 can be shutdown by grounding the RT pin (see Figure 25).
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com ICL = 40µA x RADJ/RSEN (7) When using Equation 6 or Equation 7, the tolerances for the ADJ pin current sink and the offset of the current limit comparator should be included to ensure the resulting minimum current limit is not less than the required maximum switch current.
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LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 LM25085 ADJ VIN LM25085 RADJ ADJ 40 PA 40 PA CURRENT LIMIT COMPARATOR + - VIN RADJ CURRENT LIMIT COMPARATOR CADJ + - ISEN VIN GATE DRIVER Q1 PGATE VCC RSEN CADJ ISEN VIN L1 GATE DRIVER Q1 PGATE L1 VCC D1 USING Q1 RDS(ON) D1 USING SENSE RESISTOR RSEN Figure 26.
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com If the PFET RDS(ON) is used for current limit detection, note that it typically has a positive temperature coefficient. At 100°C the RDS(ON) may be as much as 50% higher than the value at 25°C which could result in incorrect current limiting if not accounted for when determining the value of the RADJ resistor.
PAGE 15
LM25085, LM25085-Q1 www.ti.com • RT, PFET: Before selecting the RT resistor, the PFET must be selected as its turn-on and turn-off delays affect the calculated value of RT. For the Vishay Si7465 PFET, the difference of its typical turn-off and turn-on delays is 57ns. Using Equation 5 at nominal input voltage, RT calculates to be: RT = • SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 5 x (12 - 1.56V) -7 1.45 x 10 x 12 x 300 kHz - (50 ns + 57 ns) x (12 - 1.56V) 1.45 x 10 -7 - 1.4 = 90.
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LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com Using the tolerances for the ADJ pin current and the current limit comparator offset, the maximum current limit threshold calculates to: (2.1 k: x 48 PA) + 9 mV ICL(max) = 0.01: = 11A The minimum current limit thresholds calculate to: ICL(min) = • (2.1 k: x 32 PA) - 9 mV 0.01: = 5.82A The load current in each case is equal to the current limit threshold minus half the current ripple amplitude.
PAGE 17
LM25085, LM25085-Q1 www.ti.com • • • SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 A 33µF electrolytic capacitor is selected for CIN, and a 1µF ceramic capacitor is selected for CBYP. Due to the ESR of CIN, the ripple at VIN will likely be higher than the calculation indicates, and therefore it may be desirable to increase CIN to 47µF or 68µF. CBYP must be located as close as possible to the VIN and GND pins of the LM25085. The voltage rating for both capacitors must be at least 42V.
PAGE 18
LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com Final Design Example Circuit The final circuit is shown in Figure 28, and its performance is presented in Figure 29 through Figure 32. CVCC 7V to 42V Input LM25085 VIN VIN CIN 33 PF GND 0.47 PF VCC CBYP 1 PF CADJ 1000 pF ADJ RT 90.9 k: RADJ RSEN 2.1 k: 0.01: ISEN RT SHUTDOWN L1 15 PH PGATE VOUT Q1 D1 GND R3 66.5 k: C2 0.1 PF C1 3300 pF RFB2 10 k: 5V COUT 100 PF GND RFB1 FB 3.4 k: Figure 28.
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LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 Figure 31. Current Limit vs. VIN (Circuit of Figure 28) Figure 32. LM25085 Power Dissipation (Circuit of Figure 28) Alternate Output Ripple Configurations The minimum ripple configuration, using C1, C2 and R3, used in the example circuit, Figure 28, results in a low ripple amplitude at VOUT determined mainly by the characteristics of the output capacitor and the ripple current in L1.
PAGE 20
LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com LM25085 L1 PGATE VOUT Q1 D1 Cff RFB2 R4 FB COUT GND RFB1 GND Figure 33. Reduced Ripple Configuration Lowest cost configuration: This configuration, shown in Figure 34, is the same as Figure 33 except Cff is removed.
PAGE 21
LM25085, LM25085-Q1 www.ti.com SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 The voltage regulation, over-voltage, and current limit comparators are very fast and can respond to short duration noise pulses. Layout considerations are therefore critical for optimum performance. The layout must be as neat and compact as possible with all the components as close as possible to their associated pins.
PAGE 22
LM25085, LM25085-Q1 SNVS593H – OCTOBER 2008 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision G (March 2013) to Revision H • 22 Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.com 19-Jul-2013 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.
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PACKAGE MATERIALS INFORMATION www.ti.com 11-Oct-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing LM25085MM/NOPB VSSOP DGK 8 LM25085MME/NOPB VSSOP DGK LM25085MMX/NOPB VSSOP DGK LM25085MY/NOPB MSOPPower PAD LM25085MYE/NOPB SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 8 250 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 8 3500 330.0 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 11-Oct-2013 Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LM25085SDE/NOPB WSON NGQ 8 250 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 LM25085SDX/NOPB WSON NGQ 8 4500 330.0 12.4 3.3 3.3 1.0 8.0 12.
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MECHANICAL DATA DGN0008A MUY08A (Rev A) BOTTOM VIEW www.ti.
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MECHANICAL DATA NGQ0008A SDA08A (Rev A) www.ti.
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