LM34919TL/NOPB

LM34919 www.ti.com SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator Check for Samples: LM34919 FEATURES 1 • • • • • • 2 • • • • Integrated N-Channel buck switch Integrated start-up regulator Input Voltage Range: 8V to 40V No loop compensation required Ultra-Fast transient response Operating frequency remains constant with load current and input voltage Maximum switching frequency: 2.0 MHz Maximum Duty Cycle Limited During Start-Up Adjustable output voltage Valley Current Limit At 0.64A • • • • • Precision internal reference Low bias current Highly efficient operation Thermal shutdown 10-Pin DSBGA Package APPLICATIONS • • • High Efficiency Point-Of-Load (POL) Regulator Non-Isolated Telecommunication Buck Regulator Secondary High Voltage Post Regulator DESCRIPTION The LM34919 Step Down Switching Regulator features all of the functions needed to implement a low cost, efficient, buck bias regulator capable of supplying 0.6A to the load. This buck regulator contains an N-Channel Buck Switch, and is available in a 10-pin DSBGA package. The constant on-time feedback regulation scheme requires no loop compensation, results in fast load transient response, and simplifies circuit implementation. The operating frequency remains constant with line and load variations due to the inverse relationship between the input voltage and the on-time. The valley current limit results in a smooth transition from constant voltage to constant current mode when current limit is detected, reducing the frequency and output voltage, without the use of foldback. Additional features include: VCC under-voltage lockout, thermal shutdown, gate drive under-voltage lockout, and maximum duty cycle limiter. Basic Step Down Regulator 8V - 40V Input VIN VCC C3 C1 LM34919 RON BST C4 L1 RON/SD SHUTDOWN VOUT SW D1 SS R1 R3 ISEN C2 C6 FB RTN SGND R2 1 2 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. All 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. Copyright © 2007–2013, Texas Instruments Incorporated LM34919 SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 www.ti.com Connection Diagram SW D3 BST C1 C3 VCC C3 C1 SGND B1 B3 SS B3 B1 RON/SD A1 A3 FB A3 VIN D1 ISEN D2 A2 D3 D2 A2 D1 A1 RTN Figure 1. Bump Side Figure 2. Top View PIN DESCRIPTIONS 2 Pin No. Name A1 RON/SD A2 RTN A3 FB B1 SGND B3 SS C1 Description Application Information On-time control and shutdown An external resistor from VIN to this pin sets the buck switch on-time. Grounding this pin shuts down the regulator. Circuit Ground Ground for all internal circuitry other than the current limit detection. Feedback input from the regulated output Internally connected to the regulation and over-voltage comparators. The regulation level is 2.5V. Sense Ground Re-circulating current flows into this pin to the current sense resistor. Softstart An internal current source charges an external capacitor to 2.5V, providing the softstart function. ISEN Current sense The re-circulating current flows through the internal sense resistor, and out of this pin to the free-wheeling diode. Current limit is nominally set at 0.64A. C3 VCC Output from the startup regulator Nominally regulates at 7.0V. An external voltage (7V-14V) can be applied to this pin to reduce internal dissipation. An internal diode connects VCC to VIN. D1 VIN Input supply voltage Nominal input range is 8.0V to 40V. D2 SW Switching Node Internally connected to the buck switch source. Connect to the inductor, freewheeling diode, and bootstrap capacitor. D3 BST Boost pin for bootstrap capacitor Connect a 0.022 µF capacitor from SW to this pin. The capacitor is charged from VCC via an internal diode during each off-time. Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 LM34919 www.ti.com SNOSAY2E – MAY 2007 – 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) VIN to RTN 44V BST to RTN 52V SW to RTN (Steady State) -1.5V ESD Rating, Human Body Model (2) 2kV BST to VCC 44V VIN to SW 44V BST to SW 14V VCC to RTN 14V SGND to RTN -0.3V to +0.3V SS to RTN -0.3V to 4V All Other Inputs to RTN -0.3 to 7V Storage Temperature Range -65°C to +150°C Junction temperature (1) (2) 150°C Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics. The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. Operating Ratings (1) VIN 8.0V to 40V −40°C to + 125°C Junction Temperature (1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics. Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 3 LM34919 SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 www.ti.com Electrical Characteristics 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. Unless otherwise stated the following conditions apply: VIN = 12V, RON = 200kΩ. See (1). Symbol Parameter Test Conditions Min Typ Max Unit 7 7.4 V Start-Up Regulator, VCC VCCReg UVLOVCC VCC regulated output 6.6 VIN-VCC dropout voltage ICC = 0 mA, VCC = UVLOVCC + 250 mV 1.2 V VCC output impedance 0 mA ≤ ICC ≤ 5 mA, VIN = 8V 175 Ω VCC current limit (2) VCC = 0V 9.5 mA VCC under-voltage lockout threshold VCC increasing 5.7 V UVLOVCC hysteresis VCC decreasing 150 mV UVLOVCC filter delay 100 mV overdrive IQ IIN operating current Non-switching, FB = 3V, SW = Open 0.5 3 0.8 mA µs ISD IIN shutdown current RON/SD = 0V, SW = Open 75 150 µA 0.5 1.0 Ω 4.4 5.2 Switch Characteristics Rds(on) Buck Switch Rds(on) ITEST = 200 mA UVLOGD Gate Drive UVLO VBST - VSW Increasing 3.0 UVLOGD hysteresis 480 V mV Softstart Pin VSS Pull-up voltage Internal current source VSS = 1V Threshold Current out of ISEN 2.5 V 10.5 µA Current Limit ILIM 0.52 0.64 0.76 A Resistance from ISEN to SGND 140 mΩ Response time 150 ns On Timer tON - 1 On-time VIN = 10V, RON = 200 kΩ tON - 2 On-time VIN = 40V, RON = 200 kΩ Shutdown threshold Voltage at RON/SD rising Threshold hysteresis Voltage at RON/SD 2.1 2.77 3.5 700 0.45 0.8 µs ns 1.2 V 25 mV 155 ns Off Timer tOFF Minimum Off-time Regulation and Over-Voltage Comparators (FB Pin) VREF FB regulation threshold SS pin = steady state FB over-voltage threshold 2.440 2.5 2.550 V 2.9 V 1 nA Thermal shutdown temperature 175 °C Thermal shutdown hysteresis 20 °C 61 °C/W FB bias current FB = 3V Thermal Shutdown TSD Thermal Resistance θJA (1) (2) 4 Junction to Ambient 0 LFPM Air Flow Typical specifications represent the most likely parametric norm at 25°C operation. VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 LM34919 www.ti.com SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 Typical Performance Characteristics Efficiency at 800 kHz Efficiency at 2 MHz Figure 3. Figure 4. VCC vs VIN VCC vs ICC 8 7.5 7 IOUT = 0 mA, All frequencies VIN VIN = 9V 6 8 10V VIN = 8V 5 6.5 VCC (V) VCC (V) 7.0 650 kHz, IOUT = 200 mA 6.0 3 2 1.3 MHz, 5.5 4 IOUT = 200 mA VCC Externally Loaded 1 FS = 800 kHz 5.0 6.5 0 7.0 7.5 8.0 8.5 9.0 0 2 4 6 8 10 12 ICC (mA) VIN (V) Figure 5. Figure 6. ICC vs Externally Applied VCC ON-TIME vs VIN and RON Figure 7. Figure 8. Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 5 LM34919 SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 www.ti.com Typical Performance Characteristics (continued) Voltage at the RON/SD Pin Shutdown and Operating Current into VIN Figure 9. Figure 10. TYPICAL APPLICATION CIRCUIT AND BLOCK DIAGRAM 7V SERIES REGULATOR 8V-40V Input LM34919 VIN VCC C3 VCC UVLO C5 C1 + RON RON/SD ON TIMER RON START COMPLETE OFF TIMER 0.8V START COMPLETE BST GATE DRIVE UVLO C4 VIN 2.5V 10.5 PA C6 DRIVER FB RTN 6 DRIVER LOGIC SS + REGULATION COMPARATOR + OVER2.9V VOLTAGE COMPARATOR L1 LEVEL SHIFT SW VOUT THERMAL SHUTDOWN D1 CURRENT LIMIT COMPARATOR R3 R1 + 64 mV Submit Documentation Feedback + RSENSE 100 m: ISEN SGND R2 C2 Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 LM34919 www.ti.com SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 VIN 7.0V UVLO VCC SW Pin Inductor Current 2.5V SS Pin VOUT t1 t2 Figure 11. Start Up Sequence FUNCTIONAL DESCRIPTION The LM34919 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient buck bias power converter capable of supplying at least 0.6A to the load. This high voltage regulator contains an N-Channel buck switch, is easy to implement, and is available in a DSBGA package. The regulator's operation is based on a constant on-time control scheme, where the on-time is determined by VIN. This feature allows the operating frequency to remain relatively constant with load and input voltage variations. The feedback control requires no loop compensation resulting in very fast load transient response. The valley current limit detection circuit, internally set at 0.64A, holds the buck switch off until the high current level subsides. This scheme protects against excessively high current if the output is short-circuited when VIN is high. The LM34919 can be applied in numerous applications to efficiently regulate down higher voltages. Additional features include: Thermal shutdown, VCC under-voltage lockout, gate drive under-voltage lockout, and maximum duty cycle limiter. Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 7 LM34919 SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 www.ti.com Control Circuit Overview The LM34919 buck DC-DC regulator employs a control scheme based on a comparator and a one-shot on-timer, with the output voltage feedback (FB) compared to an internal reference (2.5V). If the FB voltage is below the reference the buck switch is turned on for a time period determined by the input voltage and a programming resistor (RON). Following the on-time the switch remains off until the FB voltage falls below the reference but not less than the minimum off-time. The buck switch then turns on for another on-time period. Typically, during startup, or when the load current increases suddenly, the off-times are at the minimum. Once regulation is established, the off-times are longer. When in regulation, the LM34919 operates in continuous conduction mode at heavy load currents and discontinuous conduction mode at light load currents. In continuous conduction mode current always flows through the inductor, never reaching zero during the off-time. In this mode the operating frequency remains relatively constant with load and line variations. The minimum load current for continuous conduction mode is one-half the inductor's ripple current amplitude. The operating frequency is approximately: FS = VOUT x (VIN ± 1.5V) 1.13 x 10 -10 x (RON + 1.4 k:) x VIN (1) The buck switch duty cycle is approximately equal to: VOUT tON DC = tON + tOFF = VIN (2) In discontinuous conduction mode current through the inductor ramps up from zero to a peak during the on-time, then ramps back to zero before the end of the off-time. The next on-time period starts when the voltage at FB falls below the reference - until then the inductor current remains zero, and the load current is supplied by the output capacitor. In this mode the operating frequency is lower than in continuous conduction mode, and varies with load current. Conversion efficiency is maintained at light loads since the switching losses decrease with the reduction in load and frequency. The approximate discontinuous operating frequency can be calculated as follows: 2 FS = VOUT x L1 x 1.57 x 10 RL x (RON) 20 2 (3) where RL = the load resistance. The output voltage is set by two external resistors (R1, R2). The regulated output voltage is calculated as follows: VOUT = 2.5 x (R1 + R2) / R2 (4) Output voltage regulation is based on ripple voltage at the feedback input, normally obtained from the output voltage ripple through the feedback resistors. The LM34919 requires a minimum of 25 mV of ripple voltage at the FB pin. In cases where the capacitor's ESR is insufficient additional series resistance may be required (R3). Start-Up Regulator, VCC The start-up regulator is integral to the LM34919. The input pin (VIN) can be connected directly to line voltage up to 40V, with transient capability to 44V. The VCC output regulates at 7.0V, and is current limited at 9.5 mA. Upon power up, the regulator sources current into the external capacitor at VCC (C3). When the voltage on the VCC pin reaches the under-voltage lockout threshold of 5.7V, the buck switch is enabled and the Softstart pin is released to allow the Softstart capacitor (C6) to charge up. The minimum input voltage is determined by the regulator's dropout voltage, the VCC UVLO falling threshold (≊5.55V), and the frequency. When VCC falls below the falling threshold the VCC UVLO activates to shut off the output. If VCC is externally loaded, the minimum input voltage increases. To reduce power dissipation in the start-up regulator, an auxiliary voltage can be diode connected to the VCC pin. Setting the auxiliary voltage to between 7V and 14V shuts off the internal regulator, reducing internal power dissipation. The sum of the auxiliary voltage and the input voltage (VCC + VIN) cannot exceed 52V. Internally, a diode connects VCC to VIN (see Figure 12). 8 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 LM34919 www.ti.com SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 VCC C3 BST C4 L1 LM34919 D2 SW VOUT D1 ISEN R1 R3 SGND R2 C2 FB Figure 12. Self Biased Configuration Regulation Comparator The feedback voltage at FB is compared to the voltage at the Softstart pin (2.5V). 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 stays on for the programmed on-time, causing the FB voltage to rise above 2.5V. After the on-time period, the buck switch stays off until the FB voltage falls below 2.5V. Input bias current at the FB pin is less than 100 nA over temperature. Over-Voltage Comparator The voltage at FB is compared to an internal 2.9V reference. If the voltage at FB rises above 2.9V the on-time pulse is immediately terminated. This condition can occur if the input voltage or the output load changes suddenly, or if the inductor (L1) saturates. The buck switch remains off until the voltage at FB falls below 2.5V. ON-Time Timer, and Shutdown The on-time is determined by the RON resistor and the input voltage (VIN), and is calculated from: tON = 1.13 x 10 -10 x (RON + 1.4 k:) VIN - 1.5V + 100 ns (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 RON resistor is determined from the following: RON = VOUT x (VIN - 1.5V) FS x 1.13 x 10 -10 - 1.4 k: x VIN (6) In high frequency applications the minimum value for tON is limited by the maximum duty cycle required for regulation and the minimum off-time of (155 ns, ±15%). The minimum off-time limits the maximum duty cycle achievable with a low voltage at VIN. At high values of VIN, the minimum on-time is limited to ≊ 120 ns. The LM34919 can be remotely shut down by taking the RON/SD pin below 0.8V (see Figure 13). In this mode the SS pin is internally grounded, the on-timer is disabled, and bias currents are reduced. Releasing the RON/SD pin allows normal operation to resume. The voltage at the RON/SD pin is between 1.4V and 4.0V, depending on VIN and the RON resistor. Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Product Folder Links: LM34919 9 LM34919 SNOSAY2E – MAY 2007 – REVISED FEBRUARY 2013 www.ti.com VIN Input Voltage RON LM34919 RON/SD STOP RUN Figure 13. Shutdown Implementation Current Limit Current limit detection occurs during the off-time by monitoring the recirculating current through the free-wheeling diode (D1). Referring to the Block Diagram, when the buck switch is turned off the inductor current flows through the load, into SGND, through the sense resistor, out of ISEN and through D1. If that current exceeds 0.64A the current limit comparator output switches to delay the start of the next on-time period. The next on-time starts when the current out of ISEN is below 0.64A and the voltage at FB is below 2.5V. If the overload condition persists causing the inductor current to exceed 0.64A during each on-time, that is detected at the beginning of each off-time. The operating frequency is lower due to longer-than-normal off-times. Figure 14 shows the inductor current waveform. During normal operation the load current is Io, the average of the ripple waveform. When the load resistance decreases the current ratchets up until the lower peak reaches 0.64A. During the Current Limited portion of Figure 14, the current ramps down to 0.64A during each off-time, initiating the next on-time (assuming the voltage at FB is