LM2694MT

LM2694 www.ti.com SNVS444A – MAY 2006 – REVISED APRIL 2013 LM2694 30V, 600 mA Step Down Switching Regulator Check for Samples: LM2694 FEATURES DESCRIPTION • • • • • • The LM2694 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 NChannel Buck Switch, and is available in the 3 x 3 thermally enhanced WSON-10 package and a TSSOP-14 package. The 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 undervoltage lockout, thermal shutdown, gate drive undervoltage lockout, and maximum duty cycle limiter. 1 2 • • • • • • • • Integrated N-Channel Buck Switch Integrated Start-Up Regulator Input Voltage Range: 8V to 30V No Loop Compensation Required Ultra-Fast Transient Response Operating Frequency Remains Constant with Load Current and Input Voltage Variations Maximum Duty Cycle Limited During Start-Up Adjustable Output Voltage Valley Current Limit At 0.6A Maximum Switching Frequency: 1 MHz Precision Internal Reference Low Bias Current Highly Efficient Operation Thermal Shutdown Package TYPICAL APPLICATIONS • • • High Efficiency Point-Of-Load (POL) Regulator Non-Isolated Telecommunication Buck Regulator Secondary High Voltage Post Regulator • • WSON-10 (3 mm x 3 mm) w/Exposed Pad TSSOP-14 Basic Step Down Regulator 8V - 30V Input VIN VCC C3 C1 LM2694 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 © 2006–2013, Texas Instruments Incorporated LM2694 SNVS444A – MAY 2006 – REVISED APRIL 2013 www.ti.com Connection Diagrams 1 2 3 4 5 6 7 14 NC NC SW VIN BST VCC ISEN RON/SD SGND SS RTN FB NC NC 1 13 2 12 3 11 4 10 5 SW VIN BST VCC ISEN RON/SD SGND SS RTN FB 10 9 8 7 6 9 8 Figure 1. 14-Lead TSSOP Package See Package Number PW0014A Figure 2. 10-Lead WSON Package See Package Number DSC0010A Pin Descriptions PIN NUMBER DESCRIPTION APPLICATION INFORMATION TSSOP-14 1 2 SW Switching Node Internally connected to the buck switch source. Connect to the inductor, free-wheeling diode, and bootstrap capacitor. 2 3 BST Boost pin for bootstrap capacitor Connect a 0.022 µF capacitor from SW to the BST pin. The capacitor is charged from VCC via an internal diode during the buck switch off-time. 3 4 ISEN Current sense During the buck switch off-time, the inductor current flows through the internal sense resistor, and out of the ISEN pin to the free-wheeling diode. The current limit is nominally set at 0.62A. 4 5 SGND Current Sense Ground Re-circulating current flows into this pin to the current sense resistor. 5 6 RTN Circuit Ground Ground return for all internal circuitry other than the current sense resistor. 6 9 FB Voltage feedback input from the regulated output Input to both the regulation and over-voltage comparators. The FB pin regulation level is 2.5V. 7 10 SS Softstart An internal current source charges the SS pin capacitor to 2.5V to soft-start the reference input of the regulation comparator. 8 11 RON/SD On-time control and shutdown An external resistor from VIN to the RON/SD pin sets the buck switch on-time. Grounding this pin shuts down the regulator. 9 12 VCC Output of the startup regulator The voltage at VCC is nominally regulated at 7V. Connect a 0.1 µF, or larger capacitor from VCC to ground, as close as possible to the pins. An external voltage can be applied to this pin to reduce internal dissipation. MOSFET body diodes clamp VCC to VIN if VCC > VIN. 10 13 VIN Input supply voltage Nominal input range is 8V to 30V. Input bypass capacitors should be located as close as possible to the VIN pin and RTN pins. 1,7,8,14 NC No connection. No internal connection. Can be connected to ground plane to improve heat dissipation. EP Exposed Pad Exposed metal pad on the underside of the WSON package. It is recommended to connect this pad to the PC board ground plane to aid in heat dissipation. EP 2 NAME WSON-10 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 LM2694 www.ti.com SNVS444A – MAY 2006 – 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) (3) VIN to RTN 33V BST to RTN 47V SW to RTN (Steady State) ESD Rating (4) -1.5V Human Body Model 2kV BST to VCC 33V VIN to SW 33V 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) (3) (4) 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 ensured specifications and test conditions, see the Electrical Characteristics. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications. For detailed information on soldering plastic TSSOP and WSON packages, refer to the Packaging Data Book available from TI. The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. Operating Ratings (1) VIN 8.0V to 30V −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 ensured specifications and test conditions, see the Electrical Characteristics. Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 3 LM2694 SNVS444A – MAY 2006 – REVISED APRIL 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 ensured 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 = 24V, RON = 200kΩ (1) Symbol Parameter Conditions Min Typ Max Units 6.6 7 7.4 V Start-Up Regulator, VCC VCCReg UVLOVCC VCC regulated output VIN-VCC dropout voltage ICC = 0 mA, VCC = UVLOVCC + 250 mV 1.3 VCC output impedance 0 mA ≤ ICC ≤ 5 mA, VIN = 8V 175 Ω VCC current limit (2) VCC = 0V 9 mA VCC under-voltage lockout threshold VCC increasing 5.7 V UVLOVCC hysteresis VCC decreasing 150 mV UVLOVCC filter delay 100 mV overdrive 3 µs IIN operating current Non-switching, FB = 3V 0.5 0.8 mA IIN shutdown current RON/SD = 0V 90 180 µA 0.5 1.0 Ω 4.4 5.5 V Switch Characteristics Rds(on) Buck Switch Rds(on) ITEST = 200 mA UVLOGD Gate Drive UVLO VBST - VSW Increasing 3.0 V UVLOGD hysteresis 490 mV Pull-up voltage 2.5 V Internal current source 12 µA Softstart Pin Current Limit ILIM Threshold Current out of ISEN 0.5 0.62 0.74 A Resistance from ISEN to SGND 180 mΩ Response time 150 ns On Timer tON - 1 On-time VIN = 10V, RON = 200 kΩ tON - 2 On-time VIN = 30V, RON = 200 kΩ Shutdown threshold Voltage at RON/SD rising Threshold hysteresis Voltage at RON/SD falling 2.1 2.8 3.6 900 0.45 0.8 µs ns 1.2 V 35 mV 265 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 FB bias current Thermal Shutdown TSD Thermal Resistance θJA θJC (1) (2) 4 Junction to Ambient 0 LFPM Air Flow Junction to Case WSON Package 33 TSSOP Package 40 WSON Package 8.8 TSSOP Package 5.2 °C/W °C/W 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 © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 LM2694 www.ti.com SNVS444A – MAY 2006 – REVISED APRIL 2013 Typical Performance Characteristics 7.5 8 VIN = 9V 6 FS = 100 kHz FS = 620 kHz 6.5 5 VCC (V) VCC (V) VIN t 10V 7 7.0 6.0 FS = 200 kHz VIN = 8V 4 3 2 5.5 VCC Externally Loaded Load Current = 300 mA ICC = 0 mA 5.0 6.5 7.0 7.5 8.0 1 8.5 9.0 FS = 200 kHz 0 10 9.5 0 2 4 6 8 10 VIN (V) ICC (mA) Figure 3. VCC vs VIN Figure 4. VCC vs ICC 10 8.0 7.0 RON = 500k 3.0 ON-TIME (Ps) ICC INPUT CURRENT(mA) FS = 550 kHz 6.0 5.0 4.0 FS = 200 kHz 3.0 100k 300k 1.0 50k 0.3 2.0 FS = 100 kHz 1.0 0.1 0 7 8 9 10 11 12 13 8 10 5 14 15 20 25 30 VIN (V) EXTERNALLY APPLIED VCC (V) Figure 5. ICC vs Externally Applied VCC Figure 6. ON-Time vs VIN and RON 800 3.0 600 Operating Current (FB = 3V) 2.0 500 100k IIN (PA) RON/SD PIN VOLTAGE (V) 700 RON = 50k 500k 400 300 1.0 200 Shutdown Current (RON/SD = 0V) 100 0 0 5 8 10 15 20 25 30 5 8 10 15 20 25 30 VIN (V) VIN (V) Figure 7. Voltage at RON/SD Pin Figure 8. IIN vs VIN Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 5 LM2694 SNVS444A – MAY 2006 – REVISED APRIL 2013 www.ti.com Typical Application Circuit and Block Diagram 7V SERIES REGULATOR 8V-30V Input LM2694 VIN VCC C3 VCC UVLO THERMAL SHUTDOWN C5 C1 RON ON TIMER RON /SD RON START COMPLETE + OFF TIMER 0.8V START COMPLETE BST GATE DRIVE UVLO C4 VIN 2.5V 12 PA SS C6 DRIVER FB + REGULATION COMPARATOR + OVER2.9V VOLTAGE COMPARATOR RTN 6 DRIVER LOGIC L1 LEVEL SHIFT SW VOUT1 D1 CURRENT LIMIT COMPARATOR R3 + 62 mV Submit Documentation Feedback + ISEN R1 RSENSE 100 m: SGND R2 C2 Copyright © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 LM2694 www.ti.com SNVS444A – MAY 2006 – REVISED APRIL 2013 VIN 7.0V UVLO VCC SW Pin Inductor Current 2.5V SS Pin VOUT t1 t2 Figure 9. Startup Sequence Functional Description The LM2694 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 a 30V N-Channel buck switch, is easy to implement, and is available in the TSSOP-14 and the thermally enhanced WSON-10 packages. The regulator’s operation is based on a constant on-time control scheme, where the ontime 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 0.62A, holds the buck switch off until the high current level subsides. This scheme protects against excessively high currents if the output is short-circuited when VIN is high. The functional block diagram is shown in Typical Application Circuit and Block Diagram. The LM2694 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. Control Circuit Overview The LM2694 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 for a minimum of 265 ns, and until the FB voltage falls below the reference. The buck switch then turns on for another on-time period. Typically, during start-up, or when the load current increases suddenly, the off-times are at the minimum of 265 ns. Once regulation is established, the off-times are longer. Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 7 LM2694 SNVS444A – MAY 2006 – REVISED APRIL 2013 www.ti.com When in regulation, the LM2694 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) 1.14 x 10-10 x (RON + 1.4 k:) x VIN (1) The buck switch duty cycle is equal to: VOUT tON = = tON x FS VIN tON + tOFF DC = (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 (C2). 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 reduce with the reduction in load and frequency. The approximate discontinuous operating frequency can be calculated as follows: FS = VOUT2 x L1 x 1.54 x 1020 RL x (RON)2 where • RL = the load resistance (3) 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, requiring a minimum amount of ESR for the output capacitor C2. The LM2694 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 in Typical Application Circuit and Block Diagram). Start-Up Regulator, VCC The start-up regulator is integral to the LM2694. The input pin (VIN) can be connected directly to line voltage up to 30V, with transient capability to 33V. The VCC output regulates at 7.0V, and is current limited at 9 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 (≊5.5V), 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 8V 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 47V. Internally, a diode connects VCC to VIN. See Figure 10. 8 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 LM2694 www.ti.com SNVS444A – MAY 2006 – REVISED APRIL 2013 VCC C3 BST C4 L1 LM2694 D2 SW VOUT1 D1 ISEN R1 R3 SGND R2 C2 FB Figure 10. 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 for the LM2694 is determined by the RON resistor and the input voltage (VIN), and is calculated from: tON = 1.14 x 10-10 x (RON + 1.4 k:) VIN ± 1.5V + 95 ns (5) See Figure 6. 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 1.14 x 10-10 x VIN - 1.4 k: (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 265 ns, ±15%. The minimum off-time limits the maximum duty cycle achievable with a low voltage at VIN. The minimum allowed on-time to regulate the desired VOUT at the minimum VIN is determined from the following: tON(min) = VOUT x 305 ns (VIN(min) - VOUT) (7) The LM2694 can be remotely shut down by taking the RON/SD pin below 0.8V. See Figure 11. 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 normally between 1.5V and 3.0V, depending on VIN and the RON resistor. Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Product Folder Links: LM2694 9 LM2694 SNVS444A – MAY 2006 – REVISED APRIL 2013 www.ti.com VIN Input Voltage RON LM2694 RON/SD STOP RUN Figure 11. 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 Typical Application Circuit and 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 0.62A the current limit comparator output switches to delay the start of the next on-time period if the voltage at FB is below 2.5V. The next on-time starts when the current out of ISEN is below 0.62A and the voltage at FB is below 2.5V. If the overload condition persists causing the inductor current to exceed 0.62A 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 12 illustrates 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 0.62A. During the Current Limited portion of Figure 12, the current ramps down to 0.62A during each off-time, initiating the next on-time (assuming the voltage at FB is