Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - DC/DC voltage regulator Holder WSON 8

RT/SD

VIN

RTN

BST

6V - 95V

Input

SM72485

SHUTDOWN

RCL

VCC

GND

FB2

FB1

GND

OUT

SM72485

www.ti.com

SNVS697D –JANUARY 2011–REVISED APRIL 2013

100V, 150 mA Constant On-Time Buck Switching Regulator

Check for Samples: SM72485

FEATURES

APPLICATIONS

• Renewable Energy Grade

• PV Panel Smart Junction Boxes

• Operating Input Voltage Range: 6V to 95V • Non-Isolated Telecommunication Buck

Regulator

• Integrated 100V, N-Channel Buck Switch

• Secondary High Voltage Post Regulator

• Internal Start-Up Regulator

• +42V Automotive Systems

• No Loop Compensation Required

• Ultra-Fast Transient Response

DESCRIPTION

• On Time Varies Inversely With Input Voltage

The SM72485 Step Down Switching Regulator

• Operating Frequency Remains Constant With

features all of the functions needed to implement a

Varying Line Voltage and Load Current

low cost, efficient, Buck bias regulator. This high

voltage regulator contains an 100 V N-Channel Buck

• Adjustable Output Voltage From 2.5V

Switch. The device is easy to implement and is

• Highly Efficient Operation

provided in the VSSOP and the thermally enhanced

• Precision Internal Reference

WSON package. The regulator is based on a control

scheme using an ON time inversely proportional to

• Low Bias Current

. This feature allows the operating frequency to

• Intelligent Current Limit

remain relatively constant. The control scheme

• Thermal Shutdown

requires no loop compensation. An intelligent current

• Package limit is implemented with forced OFF time, which is

inversely proportional to Vout. This scheme ensures

– VSSOP

short circuit control while providing minimum

– WSON (4mm x 4mm)

foldback. Other features include: Thermal Shutdown,

under-voltage lockout, Gate drive under-voltage

lockout, Max Duty Cycle limiter, and a pre-charge

switch.

Typical Application, Basic Step-Down Regulator

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 (22 pages)

PAGE 1
SM72485 www.ti.
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SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com Connection Diagram SW BST 1 8 VIN 2 7 VCC RCL 3 6 RT/SD RTN 4 5 FB SW 1 8 VIN BST 2 7 VCC RCL 3 6 RT/SD RTN 4 5 FB Exposed Pad on Bottom Connect to Ground Figure 1. Top View 8-Lead WSON Figure 2. Top View 8-Lead VSSOP PIN DESCIPTIONS 2 Pin Name Description Application Information 1 SW Switching Node Power switching node. Connect to the output inductor, re-circulating diode, and bootstrap capacitor.
PAGE 3
SM72485 www.ti.com SNVS697D – JANUARY 2011 – REVISED APRIL 2013 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) VIN to GND -0.3V to 100V BST to GND -0.3V to 114V SW to GND (Steady State) ESD Rating -1V (3) Human Body Model 2kV BST to VCC 100V BST to SW 14V VCC to GND 14V All Other Inputs to GND -0.
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SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com Electrical Characteristics (continued) Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction Temperature range. VIN = 48V, unless otherwise stated(1). Symbol Parameter Pre-charge switch voltage Conditions Min At 1 mA Pre-charge switch on-time Typ Max Units 0.8 V 150 ns Current Limit Current Limit Threshold 0.24 Current Limit Response Time Iswitch Overdrive = 0.
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SM72485 www.ti.com SNVS697D – JANUARY 2011 – REVISED APRIL 2013 Typical Performance Characteristics Efficiency vs. Load Current and VIN (Circuit of Figure 12) VCC vs. VIN Figure 3. Figure 4. ON-Time vs Input Voltage and RT Current Limit Off-Time vs. VFB and RCL CURRENT LIMIT OFF TIME (Ps) 35 30 25 20 15 RCL = 500k 300k 10 100k 5 50k 0 0 0.5 1.0 1.5 2.0 2.5 VFB (V) Figure 5. Figure 6. Maximum Frequency vs. VOUT and VIN ICC Current vs. Applied VCC Voltage Figure 7. Figure 8.
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SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com BLOCK DIAGRAM 6V to 95V Input C5 C1 GND SM72485 7V BIAS REGULATOR VIN VIN SENSE VCC BYPASS UVLO SWITCH Q2 THERMAL SHUTDOWN VCC C3 RT ON TIMER START 0.7V RT FINISH RT/SD BST SHUTDOWN OVER-VOLTAGE COMPARATOR 2.875V START GD SD UVLO 300 ns MIN OFF TIMER FINISH FB FINISH START CURRENT LIMIT OFF TIMER VOUT D1 R CLR Q REGULATION COMPARATOR RTN L1 SW S SET Q FB RCL C4 DRIVER LEVEL SHIFT 2.5A R CL Vin R CL 0.
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SM72485 www.ti.com F= SNVS697D – JANUARY 2011 – REVISED APRIL 2013 VOUT2 x L x 1.04 x 1020 RL x (RT)2 where • RL = the load resistance (1) In continuous conduction mode, current flows continuously through the inductor and never ramps down to zero. In this mode the operating frequency is greater than the discontinuous mode frequency and remains relatively constant with load and line variations. The approximate continuous mode operating frequency can be calculated as follows: F= VOUT 1.
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SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com The turn-on sequence is shown in Figure 10. During the initial delay (t1) VCC ramps up at a rate determined by its current limit and C3 while internal circuitry stabilizes. When VCC reaches the upper threshold of its undervoltage lock-out (UVLO, typically 5.3V) the buckswitch is enabled. The inductor current increases to the current limit threshold (ILIM) and during t2 VOUT increases as the output capacitor charges up.
PAGE 9
SM72485 www.ti.com SNVS697D – JANUARY 2011 – REVISED APRIL 2013 On-Time Generator and Shutdown The on-time for the SM72485 is determined by the RT resistor, and is inversely proportional to the input voltage (Vin), resulting in a nearly constant frequency as Vin is varied over its range. The on-time equation for the SM72485 is: TON = 1.385 x 10-10 x RT / VIN (4) RT should be selected for a minimum on-time (at maximum VIN) greater than 400 ns, for proper current limit operation.
PAGE 10
SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com Thermal Protection The SM72485 should be operated so the junction temperature does not exceed 125°C during normal operation. An internal Thermal Shutdown circuit is provided to shutdown the SM72485 in the event of a higher than normal junction temperature. When activated, typically at 165°C, the controller is forced into a low power reset state by disabling the buck switch.
PAGE 11
SM72485 www.ti.com SNVS697D – JANUARY 2011 – REVISED APRIL 2013 ESR and R3: A low ESR for C2 is generally desirable so as to minimize power losses and heating within the capacitor. However, the regulator requires a minimum amount of ripple voltage at the feedback input for proper loop operation. For the SM72485 the minimum ripple required at pin 5 is 25 mV p-p, requiring a minimum ripple at VOUT of 100 mV.
PAGE 12
SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com If the internal dissipation of the SM72485 produces excessive junction temperatures during normal operation, good use of the PC board’s ground plane can help considerably to dissipate heat. The exposed pad on the bottom of the WSON package can be soldered to a ground plane on the PC board, and that plane should extend out from beneath the IC to help dissipate the heat.
PAGE 13
SM72485 www.ti.com SNVS697D – JANUARY 2011 – REVISED APRIL 2013 Figure 13. Efficiency vs. Load Current and VIN Figure 14. Efficiency vs. VIN LOW OUTPUT RIPPLE CONFIGURATIONS For applications where low output ripple is required, the following options can be used to reduce or nearly eliminate the ripple. a) Reduced ripple configuration: In Figure 15, Cff is added across RFB2 to AC-couple the ripple at VOUT directly to the FB pin.
PAGE 14
SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com Calculate VA = VOUT - (VSW x (1 - (VOUT/VIN(min)))) where • VSW is the absolute value of the voltage at the SW pin during the off-time (typically 1V) (10) VA is the DC voltage at the RA/CA junction, and is used in the next equation.
PAGE 15
SM72485 www.ti.com SNVS697D – JANUARY 2011 – REVISED APRIL 2013 REVISION HISTORY Changes from Revision C (April 2013) to Revision D • 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 11-Apr-2013 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.
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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 SM72485MM/NOPB VSSOP DGK 8 SM72485MME/NOPB VSSOP DGK SM72485MMX/NOPB VSSOP DGK SM72485SD/NOPB WSON SM72485SDE/NOPB SM72485SDX/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.
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PACKAGE MATERIALS INFORMATION www.ti.com 11-Oct-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) SM72485MM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 SM72485MME/NOPB VSSOP DGK 8 250 210.0 185.0 35.0 SM72485MMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0 SM72485SD/NOPB WSON NGU 8 1000 210.0 185.0 35.0 SM72485SDE/NOPB WSON NGU 8 250 210.0 185.0 35.0 SM72485SDX/NOPB WSON NGU 8 4500 367.0 367.0 35.
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MECHANICAL DATA NGU0008B SDC08B (Rev A) www.ti.
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