Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - DC/DC voltage regulator Holder VSSOP 10

OUT

RT/SD

VIN

RTN

BST

FB2

FB1

6V - 75V

Input

LM34923

SHUTDOWN

GND

VCC

GND

UV2

UV1

UVO

UV STATUS

LM34923

www.ti.com

SNVS695A –MARCH 2011–REVISED FEBRUARY 2013

80-V 600-mA Constant On-Time Buck Switching Regulator

Check for Samples: LM34923

FEATURES

DESCRIPTION

The LM34923 Step Down Switching Regulator

• Operating Input Voltage Range: 6V to 75V

features all of the functions needed to implement a

• Integrated 80V, N-Channel Buck Switch

low cost, efficient Buck bias regulator. This high

• Internal Start-up Regulator

voltage regulator contains an 80V N-Channel

MOSFET Switch and a startup regulator. The device

• No Loop Compensation Required

is easy to implement and is provided in an 10-pin

• Ultra-Fast Transient Response

VSSOP package. The regulator’s control scheme

• Operating Frequency Remains Constant with

uses an on-time inversely proportional to V

. This

Line and Load Variations

feature results in the operating frequency remaining

relatively constant with line and load variations. The

• Adjustable Output voltage From 2.5V

control scheme requires no loop compensation,

• Precision Internal Reference, ±2.5%

resulting in fast transient response. An intelligent

• Intelligent Current Limit Reduces Foldback

current limit is implemented with a forced off-time

which is inversely proportional to V

OUT

. This scheme

• Programmable Input UV Detector with Status

ensures short circuit control while providing minimum

Flag Output

foldback. Other features include: Thermal Shutdown,

• Pre-charge Switch Enables Bootstrap Gate

VCC Under Voltage Lock-out, Max Duty Cycle

Drive with No Load

Limiter, a Pre-charge Switch, and a programmable

• Thermal Shutdown

Under Voltage Detector with a status flag output.

• 10-Pin VSSOP Package

APPLICATIONS

• Non-Isolated Telecommunication Buck

Regulator

• 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 (26 pages)

PAGE 1
LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 80-V 600-mA Constant On-Time Buck Switching Regulator Check for Samples: LM34923 FEATURES DESCRIPTION • • • • • • The LM34923 Step Down Switching Regulator features all of the functions needed to implement a low cost, efficient Buck bias regulator. This high voltage regulator contains an 80V N-Channel MOSFET Switch and a startup regulator. The device is easy to implement and is provided in an 10-pin VSSOP package.
PAGE 2
LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com Connection Diagram SW 1 10 BST 2 9 VCC N/C 3 8 RT RTN 4 7 FB UV 5 6 UVO VIN Figure 1. Top View 10-Lead VSSOP Table 1. Pin Descriptions Pin No. Name 1 SW Switching Node Power switching node. Connect to the output inductor, re-circulating diode or synchronous FET, and bootstrap capacitor. 2 BST Boost Pin An external capacitor is required between the BST and the SW pins (0.01uF or greater ceramic).
PAGE 3
LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 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, UV to RTN -0.3V to 80V BST to RTN -0.3V to 88V SW to RTN (Steady State) -1V to VIN + 0.3V BST to VCC 80V BST to SW 10V VCC, UVO, RT to RTN –0.3V to 10V FB, RT, to RTN -0.
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LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com Electrical Characteristics (continued) Specifications with standard type are for TJ = 25°C only; limits in boldface type apply over the full Operating Junction Temperature (TJ) range. 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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LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 Typical Performance Characteristics Efficiency at 300 kHz, 10V Efficiency Comparison at 200 kHz 100 EFFICIENCY (%) 90 6V, D1 80 24V, D1 70 7.5V, D1 60 VOUT=5V, D1=DFLS1100 50 0 100 200 300 400 500 LOAD CURRENT (mA) Figure 2. Figure 3. VCC vs. VIN VCC vs. ICC Figure 4. Figure 5. ICC vs. Externally Applied VCC On-Time vs. VIN and RT 600 5 ICC (mA) 4 3 900 kHz, D1 2 200 kHz, D1 1 DCM 0 7.5 8.0 8.5 9.0 APPLIED VCC (V) 9.
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LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com Typical Performance Characteristics (continued) 4.5 Current Limit Off-Time vs. VFB Maximum Switching Frequency Figure 8. Figure 9. Voltage at the RT Pin Operating Current into VIN VOLTAGE AT THE RT PIN (V) 77 k: 4.0 34 k: 200 k: 3.5 300 k: 3.0 2.5 RT = 500 k: 2.0 1.5 1.0 5 15 25 35 45 55 65 75 VIN (V) 6 Figure 10. Figure 11. Shutdown Current into VIN UVO Pin Low Voltage vs. Sink Current Figure 12. Figure 13.
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LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 Typical Performance Characteristics (continued) VCC UVLO vs. Temperature Gate Drive UVLO vs. Temperature Figure 14. Figure 15. VCC vs. Temperature VCC Dropout vs. Temperature Figure 16. Figure 17. VCC Output Impedance vs. Temperature VCC Current Limit vs. Temperature Figure 18. Figure 19.
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LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com Typical Performance Characteristics (continued) 8 Reference Voltage vs. Temperature On-time vs. Temperature Figure 20. Figure 21. Minimum Off-time vs. Temperature Current Limit Threshold vs. Temperature Figure 22. Figure 23. Current Limit Off-Time vs. Temperature Operating Current vs. Temperature Figure 24. Figure 25.
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LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 Typical Performance Characteristics (continued) Shutdown Current vs. Temperature RT Pin Shutdown Threshold vs. Temperature Figure 26. Figure 27. UV Pin Threshold vs. Temperature UV Hysteresis Current vs. Temperature Figure 28. Figure 29.
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LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com BLOCK DIAGRAM LM34923 Input C1 VIN VCC START -UP REGULATOR C5 C3 VCC UVLO THERMAL SHUTDOWN RT ON/OFF TIMERS 0.9 V BST RT/SD VIN 2.5V C4 FEEDBACK FB L1 Delay OVER- VOLTAGE SW DRIVER LOGIC VOUT PRE CHARGE 2.85V Current Limit One- Shot D1 CURRENT LIMIT + - R3 C2 RFB2 Vth RFB1 RUV2 2.
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LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 The LM34923 operates in discontinuous conduction mode at light load currents, and continuous conduction mode at heavy load current. In discontinuous conduction mode, current through the output inductor starts at zero and ramps up to a peak during the on-time, then ramps back to zero before the end of the off-time.
PAGE 12
LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com C3 must be located as close as possible to the VCC and RTN pins. In applications with a relatively high input voltage, power dissipation in the bias regulator is a concern. An auxiliary voltage of between 7.5V and 10V can be diode connected to the VCC pin to shut off the VCC regulator, thereby reducing internal power dissipation. The current required into the VCC pin depends on the voltage applied to VCC and the switching frequency.
PAGE 13
LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 Over-Voltage Comparator The feedback voltage at FB is compared to an internal 2.85V reference. If the voltage at FB rises above 2.85V the on-time pulse is immediately terminated. This condition can occur if the input voltage, or the output load, change suddenly. The buck switch will not turn on again until the voltage at FB falls below 2.5V.
PAGE 14
LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com During each off-time, the SW pin is at approximately 0V, and the bootstrap capacitor charges from Vcc through the internal diode. The minimum OFF timer, set to 260 ns, ensures a minimum time each cycle to recharge the bootstrap capacitor. The internal pre-charge switch at the SW pin is turned on for ≊150 ns during the minimum off-time period, ensuring sufficient voltage exists across the bootstrap capacitor for the on-time.
PAGE 15
LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 APPLICATIONS INFORMATION SELECTION OF EXTERNAL COMPONENTS A guide for determining the component values is illustrated with a design example. Refer to the Block Diagram.
PAGE 16
LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com C3: The capacitor on the VCC output provides not only noise filtering and stability, but its primary purpose is to prevent false triggering of the VCC UVLO at the buck switch on/off transitions. C3 should be no smaller than 1 µF. C2 and R3: When selecting the output filter capacitor C2, the items to consider are ripple voltage due to its ESR, ripple voltage due to its capacitance, and the nature of the load.
PAGE 17
LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 As an example, assume the application requires the following thresholds: VUVH = 15V and VUVL = 14V. Therefore VUV(HYS) = 1V. The resistor values calculate to: (14) (15) RUV2 = 200kΩ, RUV1 = 43.5kΩ Capacitor C6 is added to filter noise and ripple, which may be present on the VIN line. Where the resistor values are known, the threshold voltages and hysteresis are calculated from the following: VUVH = 2.5V + [RUV2 x ( VUVL = 2.5V x 2.
PAGE 18
LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com Figure 34. Efficiency vs. Load Current and VIN Figure 35. 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 36, Cff is added across RFB2 to AC-couple the ripple at VOUT directly to the FB pin.
PAGE 19
LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 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. L1 SW VOUT LM34923 RA FB CA C2 RFB2 CB RFB1 Figure 37.
PAGE 20
LM34923 SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 www.ti.com where RL is the inductor’s DC resistance, and the 1.1 factor is an approximation for the AC losses. If it is expected that the internal dissipation of the LM34923 will produce excessive junction temperatures during normal operation, good use of the PC board’s ground plane can help to dissipate heat. Additionally the use of wide PC board traces, where possible, can help conduct heat away from the IC.
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LM34923 www.ti.com SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013 REVISION HISTORY Changes from Original (February 2013) to Revision A • Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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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 LM34923MM/NOPB VSSOP DGS 10 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM34923MMX/NOPB VSSOP DGS 10 3500 330.0 12.4 5.3 3.4 1.4 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) LM34923MM/NOPB VSSOP DGS 10 1000 210.0 185.0 35.0 LM34923MMX/NOPB VSSOP DGS 10 3500 367.0 367.0 35.
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