Datasheet

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

RT/SD

VIN

RTN

BST

6V - 95V

Input

LM5008A

SHUTDOWN

RCL

VCC

GND

FB2

FB1

GND

OUT

LM5008A

www.ti.com

SNVS583F –MARCH 2009–REVISED MARCH 2013

100-V 350-mA Constant On-Time Buck Switching Regulator

Check for Samples: LM5008A

FEATURES

DESCRIPTION

The LM5008A is a functional variant of the LM5008

• Operating input voltage range: 6V to 95V

COT Buck Switching Regulator. The functional

• Integrated 100V N-Channel buck switch

differences of the LM5008A are: the minimum input

• Internal start-up regulator

operating voltage is 6 V, the on-time equation is

slightly different, and the requirement for a minimum

• No loop compensation required

load current is removed.

• Ultra-fast transient response

The LM5008A Step Down Switching Regulator

• On time varies inversely with input voltage

features all of the functions needed to implement a

• Operating frequency remains constant with

low cost, efficient, Buck bias regulator. This high

varying line voltage and load current

voltage regulator contains an 100 V N-Channel Buck

• Adjustable output voltage from 2.5V

Switch. The device is easy to implement and is

provided in the VSSOP-8 and the thermally enhanced

• Highly efficient operation

WSON-8 packages. The regulator is based on a

• Precision internal reference

control scheme using an ON time inversely

• Low bias current

proportional to V

. This feature allows the operating

frequency to remain relatively constant. The control

• Intelligent current limit

scheme requires no loop compensation. An intelligent

• Thermal shutdown

current limit is implemented with forced OFF time,

• VSSOP-8 and WSON-8 (4mm x 4mm) packages

which is inversely proportional to Vout. This scheme

ensures short circuit control while providing minimum

APPLICATIONS foldback. Other features include: Thermal Shutdown,

under-voltage lockout, Gate drive under-voltage

• Non-Isolated Telecommunication Buck

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

Regulator

switch.

• Secondary High Voltage Post Regulator

• +42V Automotive Systems

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 (23 pages)

PAGE 1
LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 2013 100-V 350-mA Constant On-Time Buck Switching Regulator Check for Samples: LM5008A FEATURES DESCRIPTION • • • • • • • The LM5008A is a functional variant of the LM5008 COT Buck Switching Regulator. The functional differences of the LM5008A are: the minimum input operating voltage is 6 V, the on-time equation is slightly different, and the requirement for a minimum load current is removed.
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LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 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 Functions Table 1. Pin Descriptions Pin Name 1 SW Switching Node Power switching node. Connect to the output inductor, re-circulating diode, and bootstrap capacitor.
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LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 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) VIN to GND -0.3V to 100V BST to GND -0.3V to 114V SW to GND (Steady State) -1V ESD Rating, Human Body Model (2) 2kV BST to VCC 100V BST to SW 14V VCC to GND 14V All Other Inputs to GND -0.
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LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 2013 www.ti.com Electrical Characteristics 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 Conditions Min Typ Max 7 7.4 Unit VCC Supply Vcc Reg Vcc Regulator Output Vin = 48V Vin – Vcc 6V < Vin < 8.5V Vcc Bypass Threshold Vin Increasing 6.6 100 V mV 8.
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LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 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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LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 2013 www.ti.com BLOCK DIAGRAM 6V to 95V Input C5 C1 GND 7V BIAS REGULATOR VIN VIN SENSE LM5008A 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 C4 DRIVER L1 LEVEL SHIFT 2.5V SW S SET Q FB FB FINISH START CURRENT LIMIT OFF TIMER R CL R CL RTN VOUT D1 R CLR Q REGULATION COMPARATOR RCL Vin 0.
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LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 2013 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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LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 2013 VIN www.ti.com t1 7V UVLO VCC Vin SW Pin 0V I LIM Inductor Current IO t2 t3 VOUT Figure 10. Startup Sequence Regulation Comparator The feedback voltage at FB is compared to an internal 2.5V reference. In normal operation (the output voltage is regulated), an on-time period is initiated when the voltage at FB falls below 2.5V. The buck switch will stay on for the on-time, causing the FB voltage to rise above 2.5V.
PAGE 9
LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 2013 RT should be selected for a minimum on-time (at maximum VIN) greater than 400 ns, for proper current limit operation. This requirement limits the maximum frequency for each application, depending on VIN and VOUT. The LM5008A can be remotely disabled by taking the RT/SD pin to ground. See Figure 11. The voltage at the RT/SD pin is between 1.5 and 3.0 volts, depending on Vin and the value of the RT resistor.
PAGE 10
LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 2013 www.ti.com Thermal Protection The LM5008A 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 LM5008A 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
LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 2013 APPLICATIONS INFORMATION SELECTION OF EXTERNAL COMPONENTS A guide for determining the component values will be illustrated with a design example. Refer to the Block Diagram. The following steps will configure the LM5008A for: • Input voltage range (Vin): 12V to 95V • Output voltage (VOUT1): 10V • Load current (for continuous conduction mode): 100 mA to 300 mA RFB1, RFB2: VOUT = VFB x (RFB1 + RFB2) / RFB1, and since VFB = 2.
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LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 2013 www.ti.com RCL: When current limit is detected, the minimum off-time set by this resistor must be greater than the maximum normal off-time, which occurs at maximum input voltage. Using Equation 4, the minimum on-time is 472 ns, yielding an off-time of 4 µs (at 223 kHz). Due to the 25% tolerance on the on-time, the off-time tolerance is also 25%, yielding a maximum off-time of 5 µs.
PAGE 13
LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 2013 12 - 95V Input VCC VIN 7 8 C1 1.0 PF C3 0.47 PF C5 0.1 PF BST RT 2 324k RT/SD C4 0.01 PF LM5008A 6 L1 220 PH 10.0V SW VOUT 1 SHUTDOWN D1 RCL RFB2 3.01k R3 RFB1 1.0k C2 22 PF 3.0 3 RCL 332k FB RTN 5 4 GND Figure 12. LM5008A Example Circuit Table 2.
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LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 2013 www.ti.com 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 15
LM5008A www.ti.com SNVS583F – MARCH 2009 – REVISED MARCH 2013 where • tON is the maximum on-time (at minimum input voltage), and ΔV is the desired ripple amplitude at the RA/CA junction (typically 40-50 mV). RA and CA are then chosen from standard value components to satisfy the above product. Typically CA is 1000 pF to 5000 pF, and RA is 10 kΩ to 300 kΩ. CB is then chosen large compared to CA, typically 0.1 µF. (11) L1 SW VOUT LM5008A RA FB CA C2 RFB2 CB RFB1 Figure 16.
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LM5008A SNVS583F – MARCH 2009 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision E (March 2013) to Revision F • 16 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.
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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 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LM5008AMMX/NOPB VSSOP DGK 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM5008ASD/NOPB WSON NGU 8 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 LM5008ASDX/NOPB WSON NGU 8 4500 330.0 12.4 4.3 4.3 1.3 8.0 12.
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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) LM5008AMMX/NOPB LM5008ASD/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0 WSON NGU 8 1000 210.0 185.0 35.0 LM5008ASDX/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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