LM34910 www.ti.com SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 LM34910 High Voltage (40V, 1.25A) Step Down Switching Regulator Check for Samples: LM34910 FEATURES DESCRIPTION • • • • • • The LM34910 Step Down Switching Regulator features all of the functions needed to implement a low cost, efficient, buck bias regulator capable of supplying 1.25A to the load. This buck regulator contains a 40V N-Channel Buck Switch, and is available in the thermally enhanced WSON-10 package. The hysteretic 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 current limit detection is set at 1.25A. Additional features include: VCC under-voltage lockout, thermal shutdown, gate drive under-voltage lockout, and maximum duty cycle limiter. 1 2 • • • • • • • Integrated 40V, N-Channel Buck Switch Integrated Start-Up Regulator Input Voltage Range: 8V to 36V No Loop Compensation Required Ultra-Fast Transient Response Operating Frequency Remains Constant with Load Current and Input Voltage Maximum Duty Cycle Limited During Start-Up Adjustable Output Voltage Valley Current Limit At 1.25A Precision Internal Reference Low Bias Current Highly Efficient Operation Thermal Shutdown • • TYPICAL APPLICATIONS • • • Package WSON-10 (4 mm x 4 mm) Exposed Thermal Pad For Dissipation High Efficiency Point-Of-Load (POL) Regulator Non-Isolated Telecommunication Buck Regulator Secondary High Voltage Post Regulator Improved Heat Connection Diagram SW 1 10 VIN BST 2 9 VCC ISEN 3 8 RON/SD SGND 4 7 SS RTN 5 6 FB Figure 1. 10-Lead WSON See DPR0010A Package 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. 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Copyright © 2004–2013, Texas Instruments Incorporated LM34910 SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 www.ti.com Typical Application Circuit and Block Diagram 7V SERIES REGULATOR 8V-36V Input LM34910 10 VIN VCC 9 C3 VCC UVLO C5 THERMAL SHUTDOWN C1 RON RON/ 8 SD 280 ns OFF TIMER ON TIMER RON + 0.7V START COMPLETE START COMPLETE BST 2 GATE DRIVE UVLO C4 VIN 2.5V 11.5 PA 7 DRIVER LOGIC SS C6 DRIVER L1 LEVEL SHIFT SW 1 VOUT1 + REGULATION COMPARATOR + OVER-VOLTAGE 2.875V COMPARATOR 6 FB D1 CURRENT LIMIT COMPARATOR R3 + - 5 RTN 62.5 mV + ISEN 3 R1 RSENSE 50 m: SGND 4 R2 VOUT2 C2 PIN DESCRIPTIONS PIN NAME DESCRIPTION APPLICATION INFORMATION 1 SW Switching Node Internally connected to the buck switch source. Connect to the external inductor, diode, and boost capacitor. 2 BST Boost pin for boot-strap capacitor Connect a 0.022 µF capacitor from SW to this pin. An internal diode charges the capacitor during the off-time. 3 ISEN Current sense input Internally the current sense resistor connects from this pin to SGND. Re-circulating current flows out of this pin to the freewheeling diode. Current limit is set at 1.25A. 4 SGND Sense Ground Re-circulating current flows into this pin to the current sense resistor. 5 RTN Circuit Ground Ground for all internal circuitry other than the current limit detection. 6 FB Feedback Internally connected to the regulation and over-voltage comparators. The regulation level is 2.5V. 7 SS Softstart An internal 11.5 µA current source charges an external capacitor to 2.5V to provide the softstart function. 8 RON/SD 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. 9 VCC Output from the start-up regulator Nominally regulated to 7.0V. An external voltage (8V-14V) can be connected to this pin to reduce internal dissipation. An internal diode connects VCC to VIN. 10 VIN Input supply voltage Nominal input range is 8.0V to 36V. 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. 2 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 LM34910 www.ti.com SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 Absolute Maximum Ratings (1) (2) VIN to GND 40V BST to GND 50V SW to GND (Steady State) -1.5V ESD Rating (3) Human Body Model 2kV BST to VCC 40V VIN to SW 40V BST to SW 14V VCC to GND 14V SGND to RTN -0.3V to +0.3V Current out of ISEN See Text SS to RTN -0.3V to 4V All Other Inputs to GND -0.3 to 7V Storage Temperature Range -55°C to +150°C JunctionTemperature 150°C (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 guaranteed specifications and test conditions, see the Electrical Characteristics. For detailed information on soldering plastic WSON packages, refer to the Packaging Data Book available from National Semiconductor Corporation. The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. (2) (3) Operating Ratings (1) VIN 8.0V to 36V −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 guaranteed specifications and test conditions, see the Electrical Characteristics. Electrical Characteristics Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction Temperature range. VIN = 24V, RON = 200k unless otherwise stated (1). Symbol Parameter Conditions Min Typ Max Units 6.6 7 7.4 V Start-Up Regulator, VCC VCCReg VCC regulated output VIN-VCC dropout voltage ICC = 0 mA, VCC = VCCReg - 100 mV 1.4 V VCC output impedance 0 mA ≤ ICC ≤ 5 mA 140 Ω VCC current limit UVLOVCC (2) 9 mA VCC under-voltage lockout threshold VCC = 0V VCC increasing 5.8 V UVLOVCC hysteresis VCC decreasing 150 mV UVLOVCC filter delay 100 mV overdrive IIN operating current Non-switching, FB = 3V IIN shutdown current RON/SD = 0V 3 µs 0.63 1 mA 80 250 µA 0.45 0.95 Ω 4.3 5.5 V Switch Characteristics Rds(on) Buck Switch Rds(on) ITEST = 200 mA UVLOGD Gate Drive UVLO VBST - VSW Increasing UVLOGD hysteresis 3.0 440 mV Softstart Pin (1) (2) Pull-up voltage 2.5 V Internal current source 11.5 µA 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 © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 3 LM34910 SNVS297B – OCTOBER 2004 – REVISED MARCH 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 = 24V, RON = 200k unless otherwise stated (1). Symbol Parameter Conditions Min Typ Max 1 1.25 1.5 Units Current Limit ILIM Threshold Current out of ISEN A Resistance from ISEN to SGND 130 mΩ Response time 150 ns On Timer tON - 1 On-time VIN = 10V, RON = 200 kΩ tON - 2 On-time VIN = 36V, RON = 200 kΩ Shutdown threshold Voltage at RON/SD rising Threshold hysteresis Voltage at RON/SD falling 2.1 2.75 3.6 740 0.35 0.65 µs ns 1.1 V 40 mV 280 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 2.875 V 100 nA Thermal shutdown temperature 175 °C Thermal shutdown hysteresis 20 °C FB bias current Thermal Shutdown TSD 4 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 LM34910 www.ti.com SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 Typical Performance Characteristics 7.0 7.5 RON = 400k 6.0 RON = 200k 7.0 S FS = 730 kHz 6.0 ON-TIME (Ps) kH = 19 4 6.5 F VCC (V) z FS = 100 kHz 5.0 RON = 100k 4.0 RON = 44.2k 3.0 2.0 5.5 Load Current = 500 mA 1.0 0 5.0 6.5 7.0 7.5 8.0 8.5 9.0 0 10 20 30 40 VIN (V) VIN (V) Figure 2. VCC vs VIN Figure 3. ON-Time vs VIN and RON Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 5 LM34910 SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 www.ti.com Functional Description The LM34910 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient buck bias power converter capable of supplying 1.25A to the load. This high voltage regulator contains a 40V NChannel buck switch, is easy to implement, and is available in the thermally enhanced WSON-10 package. The regulator’s operation is based on a hysteretic control scheme, and uses an on-time control which varies inversely with VIN. This feature allows the operating frequency to remain relatively constant with load and input voltage variations. The hysteretic control requires no loop compensation resulting in very fast load transient response. The valley current limit detection circuit, internally set at 1.25A, holds the buck switch off until the high current level subsides. The functional block diagram is shown in Typical Application Circuit and Block Diagram. The LM34910 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. Hysteretic Control Circuit Overview The LM34910 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 280 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 280 ns. Once regulation is established, the off-times are longer. When in regulation, the LM34910 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: VOUT FS = 1.3 x 10-10 x RON (1) The buck switch duty cycle is 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 (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: VOUT2 x L1 x 1.18 x 1020 FS = RL x (RON)2 where • 6 RL = the load resistance (3) Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 LM34910 www.ti.com SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 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 LM34910 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). For applications where lower output voltage ripple is required the output can be taken directly from a low ESR output capacitor as shown in Figure 4. However, R3 slightly degrades the load regulation. L1 SW LM34910 R1 R3 FB VOUT2 R2 C2 Figure 4. Low Ripple Output Configuration Start-up Regulator, VCC The start-up regulator is integral to the LM34910. The input pin (VIN) can be connected directly to line voltage up to 36V, with transient capability to 40V. The VCC output regulates at 7.0V, and is current limited to 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 5.8V, 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 (≊5.7V), 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 since the output impedance at VCC is ≊140Ω. See Figure 2. 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 50V. Internally, a diode connects VCC to VIN. See Figure 5. VCC C3 BST C4 L1 LM34910 D2 SW VOUT1 D1 ISEN R1 R3 VOUT2 SGND R2 C2 FB Figure 5. Self Biased Configuration Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 7 LM34910 SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 www.ti.com 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 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. Bias current at the FB pin is nominally 100 nA. Over-Voltage Comparator The voltage at FB is compared to an internal 2.875V reference. If the voltage at FB rises above 2.875V the ontime 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 LM34910 is determined by the RON resistor and the input voltage (VIN), and is calculated from: 1.3 x 10-10 x RON tON = VIN (5) See Figure 3. The inverse relationship with VIN results in a nearly constant frequency as VIN is varied. RON should be selected for a minimum on-time (at maximum VIN) greater than 200 ns. This requirement limits the maximum frequency for each application, depending on VIN and VOUT, calculated from the following: VOUT FMAX = VINMAX x 200 ns (6) The LM34910 can be remotely shut down by taking the RON/SD pin below 0.65V. See Figure 6. 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 1.5V and 3.0V, depending on VIN and the RON resistor. VIN Input Voltage RON LM34910 RON/SD STOP RUN Figure 6. 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 1.25A 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 1.25A and the voltage at FB is below 2.5V. If the overload condition persists causing the inductor current to exceed 1.25A during each on-time, that is detected at the beginning of each off-time. The operating frequency may be lower due to longer-than-normal off-times. 8 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 LM34910 www.ti.com SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 Figure 7 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 1.25A. During the Current Limited portion of Figure 7, the current ramps down to 1.25A during each off-time, initiating the next on-time (assuming the voltage at FB is <2.5V). During each on-time the current ramps up an amount equal to: ΔI = (VIN - VOUT) x tON / L1 (7) During this time the LM34910 is in a constant current mode, with an average load current (IOCL) equal to 1.25A + ΔI/2. IPK 'I IOCL Inductor Current 1.25A IO Normal Operation Load Current Increases Current Limited Figure 7. Inductor Current - Current Limit Operation The current limit threshold can be increased by connecting an external resistor between SGND and ISEN. The external resistor will typically be less than 1Ω. The peak current out of SW and ISEN must not exceed 3.5A. The average current out of SW must be less than 3A, and the average current out of ISEN must be less than 2A. Therefore IPK in Figure 7 must not exceed 3.5A, and IOCL must not exceed 2A. N - Channel Buck Switch and Driver The LM34910 integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak current allowed through the buck switch is 3.5A, and the maximum allowed average current is 3A. The gate driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. A 0.022 µF capacitor (C4) connected between BST and SW provides the voltage to the driver during the on-time. During each off-time, the SW pin is at approximately -1V, and C4 charges from VCC through the internal diode. The minimum off-time of 280 ns ensures a minimum time each cycle to recharge the bootstrap capacitor. Softstart The softstart feature allows the converter to gradually reach a steady state operating point, thereby reducing start-up stresses and current surges. Upon turn-on, after VCC reaches the under-voltage threshold, an internal 11.5 µA current source charges up the external capacitor at the SS pin to 2.5V. The ramping voltage at SS (and the non-inverting input of the regulation comparator) ramps up the output voltage in a controlled manner. An internal switch grounds the SS pin if VCC is below the under-voltage lockout threshold, if a thermal shutdown occurs, or if the RON/SD pin is grounded. Thermal Shutdown The LM34910 should be operated so the junction temperature does not exceed 125°C. If the junction temperature increases, an internal Thermal Shutdown circuit, which activates (typically) at 175°C, takes the controller to a low power reset state by disabling the buck switch and the on-timer, and grounding the Softstart pin. This feature helps prevent catastrophic failures from accidental device overheating. When the junction temperature reduces below 155°C (typical hysteresis = 20°C), the Softstart pin is released and normal operation resumes. Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 9 LM34910 SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 www.ti.com APPLICATIONS INFORMATION EXTERNAL COMPONENTS The following guidelines can be used to select the external components. R1 and R2: The ratio of these resistors is calculated from: R1/R2 = (VOUT/2.5V) - 1 (8) R1 and R2 should be chosen from standard value resistors in the range of 1.0 kΩ - 10 kΩ which satisfy the above ratio. RON: The minimum value for RON is calculated from: 200 ns x VINMAX RON t 1.3 x 10-10 (9) Equation 1 can be used to select RON if a specific frequency is desired as long as the above limitation is met. L1: The main parameter affected by the inductor is the output current ripple amplitude (IOR). The limits for IOR must be determined at both the minimum and maximum nominal load currents. a) If the maximum load current is less than the current limit threshold (1.25A), the minimum load current is used to determine the maximum allowable ripple. To maintain continuous conduction mode the lower peak should not reach 0 mA. For this case, the maximum ripple current is: IOR(MAX1) = 2 x IO(min) (10) The ripple calculated in Equation 10 is then used in the following equation: VOUT x (VIN - VOUT) L1 = IOR x FS x VIN (11) where VIN is the maximum input voltage and Fs is determined from Equation 1. This provides a minimum value for L1. The next larger standard value should be used, and L1 should be rated for the IPK current level. b) If the maximum load current is greater than the current limit threshold (1.25A), the LM34910 ensures the lower peak reaches 1.25A each cycle, requiring that IOR be at least twice the difference. The upper peak, however, must not exceed 3.5A. For this case, the ripple limits are: IOR(MAX2) = 2 x (3.5A - IO(max)) (12) IOR(MIN1) = 2 x (IO(max) - 1.25A) (13) and The lesser of Equation 12 and Equation 13 is then used in Equation 11. If IOR(MAX2) is used, the maximum VIN is used in Equation 11. The next larger value should then be used for L1. If IOR(MIN1) is used, the minimum VIN is used in Equation 11. The next smaller value should then be used for L1. L1 must be rated for the peak value of the current waveform (IPK in Figure 7). C3: The capacitor on the VCC output provides not only noise filtering and stability, but also prevents false triggering of the VCC UVLO at the buck switch on/off transitions. For this reason, C3 should be no smaller than 0.1 µF, and should be a good quality, low ESR, ceramic capacitor. C2, and R3: Since the LM34910 requires a minimum of 25 mVp-p of ripple at the FB pin for proper operation, the required ripple at VOUT1 is increased by R1 and R2. This necessary ripple is created by the inductor ripple current acting on C2’s ESR + R3. The minimum ripple current is calculated using Equation 11, rearranged to solve for IOR at minimum VIN. The minimum ESR for C2 is then equal to: 25 mV x (R1 + R2) ESR(min) = 10 R2 x IOR(min) (14) Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 LM34910 www.ti.com SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 If the capacitor used for C2 does not have sufficient ESR, R3 is added in series as shown in Typical Application Circuit and Block Diagram. Generally R3 is less than 1Ω. C2 should generally be no smaller than 3.3 µF, although that is dependent on the frequency and the allowable ripple amplitude at VOUT1. Experimentation is usually necessary to determine the minimum value for C2, as the nature of the load may require a larger value. A load which creates significant transients requires a larger value for C2 than a non-varying load. D1: The important parameters are reverse recovery time and forward voltage. The reverse recovery time determines how long the reverse current surge lasts each time the buck switch is turned on. The forward voltage drop is significant in the event the output is short-circuited as it is mainly this diode’s voltage (plus the voltage across the current limit sense resistor) which forces the inductor current to decrease during the off-time. For this reason, a higher voltage is better, although that affects efficiency. A reverse recovery time of ≊30 ns, and a forward voltage drop of ≊0.75V are preferred. The reverse leakage specification is important as that can significantly affect efficiency. D1’s reverse voltage rating must be at least as great as the maximum VIN, and its current rating must equal or exceed IPK Figure 7. C1 and C5: C1’s purpose is to supply most of the switch current during the on-time, and limit the voltage ripple at VIN, on the assumption that the voltage source feeding VIN has an output impedance greater than zero. If the source’s dynamic impedance is high (effectively a current source), it supplies the average input current, but not the ripple current. At maximum load current, when the buck switch turns on, the current into VIN suddenly increases to the lower peak of the inductor’s ripple current, ramps up to the peak value, then drop to zero at turn-off. The average current during the on-time is the load current. For a worst case calculation, C1 must supply this average load current during the maximum on-time. C1 is calculated from: IO x tON C1 = 'V (15) where Io is the load current, tON is the maximum on-time, and ΔV is the allowable ripple voltage at VIN. C5’s purpose is to help avoid transients and ringing due to long lead inductance at VIN. A low ESR, 0.1 µF ceramic chip capacitor is recommended, located close to the LM34910 . C4: The recommended value for C4 is 0.022 µF. A high quality ceramic capacitor with low ESR is recommended as C4 supplies a surge current to charge the buck switch gate at turn-on. A low ESR also helps ensure a complete recharge during each off-time. C6: The capacitor at the SS pin determines the softstart time, i.e. the time for the reference voltage at the regulation comparator, and the output voltage, to reach their final value. The time is determined from the following: tSS = C6 x 2.5V 11.5 PA (16) PC BOARD LAYOUT The LM34910 regulation, over-voltage, and current limit comparators are very fast, and respond to short duration noise pulses. Layout considerations are therefore critical for optimum performance. The layout must be as neat and compact as possible, and all of the components must be as close as possible to their associated pins. The current loop formed by D1, L1, C2 and the SGND and ISEN pins should be as small as possible. The ground connection from C2 to C1 should be as short and direct as possible. If it is expected that the internal dissipation of the LM34910 will produce 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 IC package can be soldered to a ground plane, and that plane should extend out from beneath the IC, and be connected to ground plane on the board’s other side with several vias, to help dissipate the heat. The exposed pad is internally connected to the IC substrate. Additionally the use of wide PC board traces, where possible, can help conduct heat away from the IC. Judicious positioning of the PC board within the end product, along with the use of any available air flow (forced or natural convection) can help reduce the junction temperatures. Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 11 LM34910 SNVS297B – OCTOBER 2004 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision A (March 2013) to Revision B • 12 Page Changed layout of National Data Sheet to TI format .......................................................................................................... 11 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM34910 PACKAGE OPTION ADDENDUM www.ti.com 1-Nov-2015 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (°C) Device Marking (4/5) LM34910SD NRND WSON DPR 10 TBD Call TI Call TI -40 to 125 34910SD LM34910SD/NOPB ACTIVE WSON DPR 10 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 34910SD LM34910SDX/NOPB ACTIVE WSON DPR 10 4500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 34910SD (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. 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Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 2-Sep-2015 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 LM34910SD/NOPB WSON DPR 10 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 LM34910SDX/NOPB WSON DPR 10 4500 330.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 2-Sep-2015 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM34910SD/NOPB WSON DPR 10 1000 210.0 185.0 35.0 LM34910SDX/NOPB WSON DPR 10 4500 367.0 367.0 35.0 Pack Materials-Page 2 MECHANICAL DATA DPR0010A SDC10A (Rev A) www.ti.com IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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