LP38858 1.5A Fast-Response High-Accuracy LDO Linear Regulator with Soft-Start General Description Features The LP38858 is a high current, fast response regulator which can maintain output voltage regulation with extremely low input to output voltage drop. Fabricated on a CMOS process, the device operates from two input voltages: VBIAS provides voltage to drive the gate of the N-MOS power transistor, while VIN is the input voltage which supplies power to the load. The use of an external bias rail allows the part to operate from ultra low VIN voltages. Unlike bipolar regulators, the CMOS architecture consumes extremely low quiescent current at any output load current. The use of an N-MOS power transistor results in wide bandwidth, yet minimum external capacitance is required to maintain loop stability. The fast transient response of this device makes it suitable for use in powering DSP, Microcontroller Core voltages and Switch Mode Power Supply post regulators. The LP38858 is available in TO-220 and TO-263 5-Lead packages. Dropout Voltage: 130mV (typical) at 1.5A load current. Low Ground Pin Current: 14 mA (typical) at 1.5A load current. Soft-Start: Programmable Soft-Start time. Precision Output Voltage: ±1.0% for TJ = 25°C and ±2.0% for 0°C ≤ TJ ≤ +125°C, across all line and load conditions ■ ■ ■ ■ ■ ■ ■ ■ ■ Standard VOUT values of 0.8V and 1.2V Wide VBIAS Supply operating range of 3.0V to 5.5V Stable with 10µF Ceramic capacitors Dropout voltage of 130 mV (typical) at 1.5A load current Precision Output Voltage across all line and load conditions: — ±1.0% VOUT for TJ = 25°C — ±2.0% VOUT for 0°C ≤ TJ ≤ +125°C — ±3.0% VOUT for -40°C ≤ TJ ≤ +125°C Over-Temperature and Over-Current protection Available in 5 lead TO-220 and TO-263 packages Custom VOUT values between 0.8V and 1.2V are available −40°C to +125°C Operating Temperature Range Applications ■ ASIC Power Supplies In: - Desktops, Notebooks, and Graphics Cards, Servers - Gaming Set Top Boxes, Printers and Copiers ■ Server Core and I/O Supplies ■ DSP and FPGA Power Supplies ■ SMPS Post-Regulator Typical Application Circuit 20202701 © 2007 National Semiconductor Corporation 202027 www.national.com LP38858 1.5A Fast-Response High-Accuracy LDO Linear Regulator with Soft-Start November 2006 LP38858 Ordering Information VOUT * Order Number Package Type Package Drawing LP38858S-0.8 TO263-5 TS5B Rail of 45 0.8V LP38858SX-0.8 TO263-5 TS5B Tape and Reel of 500 LP38858T-0.8 TO220-5 T05D Rail of 45 1.2V Supplied As LP38858S-1.2 TO263-5 TS5B Rail of 45 LP38858SX-1.2 TO263-5 TS5B Tape and Reel of 500 LP38858T-1.2 TO220-5 T05D Rail of 45 * For custom VOUT values between 0.8V and 1.2V please contact the National Semiconductor Sales Office. Connection Diagrams 20202702 20202703 TO263–5, Top View TO220–5, Top View Pin Descriptions TO220–5 and TO263–5 Packages Pin # Pin Symbol 1 SS Soft-Start capacitor connection. Used to slow the rise time of VOUT at turn-on. 2 IN The unregulated voltage input pin. 3 GND Ground 4 OUT The regulated output voltage pin. 5 BIAS The supply for the internal control and reference circuitry. TAB TAB The TAB is a thermal connection that is physically attached to the backside of the die, and used as a thermal heat-sink connection. See the Application Information section for details. www.national.com Pin Description 2 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature Range Lead Temperature Soldering, 5 seconds ESD Rating Human Body Model (Note 2) Power Dissipation (Note 3) VIN Supply Voltage (Survival) VBIAS Supply Voltage (Survival) −65°C to +150°C Operating Ratings 260°C (Note 1) VIN Supply Voltage VBIAS Supply Voltage IOUT Junction Temperature Range (Note 3) ±2 kV Internally Limited −0.3V to +6.0V −0.3V to +6.0V −0.3V to +6.0V −0.3V to +6.0V Internally Limited −40°C to +150°C (VOUT + VDO) to VBIAS 3.0V to 5.5V 0 mA to 1.5A −40°C to +125°C Electrical Characteristics Unless otherwise specified: VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, IOUT = 10 mA, CIN = COUT = 10 µF, CBIAS = 1 µF, CSS = open. Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are guaranteed 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. Symbol Parameter Conditions VOUT(NOM) + 1V ≤ VIN ≤ VBIAS, 3.0V ≤ VBIAS ≤ 5.5V, 10 mA ≤ IOUT ≤ 1.5A VOUT VOUT Accuracy MIN TYP MAX -1.0 -3.0 0 1.0 3.0 VOUT(NOM) + 1V ≤ VIN ≤ VBIAS, 3.0V ≤ VBIAS ≤ 5.5V, 10 mA ≤ IOUT ≤ 1.5A, Units % -2.0 0 2.0 0°C ≤ TJ ≤ +125°C Line Regulation, VIN (Note 4) VOUT(NOM) + 1V ≤ VIN ≤ VBIAS - 0.04 - %/V ΔVOUT/ΔVBIAS Line Regulation, VBIAS (Note 4) 3.0V ≤ VBIAS ≤ 5.5V - 0.10 - %/V ΔVOUT/ΔIOUT Output Voltage Load Regulation (Note 5) 10 mA ≤ IOUT ≤ 1.5A - 0.2 - %/A Dropout Voltage (Note 6) IOUT = 1.5A - 130 165 180 mV - 7.0 8.5 9.0 11 12 15 - 3.0 3.8 4.5 mA 2.20 2.00 2.45 2.70 2.90 V 60 50 150 300 350 mV - 4.5 - A LP38858-0.8 11.0 13.5 16.0 LP38858-1.2 13.5 16.0 18.5 LP38858-0.8, CSS = 10 nF - 675 - LP38858-1.2, CSS = 10 nF - 800 - ΔVOUT/ΔVIN VDO LP38858-0.8 IGND(IN) Quiescent Current Drawn from VIN Supply 10 mA ≤ IOUT ≤ 1.5A LP38858-1.2 10 mA ≤ IOUT ≤ 1.5A Quiescent Current Drawn from VBIAS Supply 10 mA ≤ IOUT ≤ 1.5A UVLO Under-Voltage Lock-Out Threshold VBIAS rising until device is functional UVLO(HYS) Under-Voltage Lock-Out Hysteresis VBIAS falling from UVLO threshold until device is non-functional Output Short-Circuit Current VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, VOUT = 0.0V IGND(BIAS) ISC mA Soft-Start rSS Soft-Start internal resistance tSS Soft-Start time tSS = CSS × rSS × 5 3 kΩ μs www.national.com LP38858 VSS Soft-Start Voltage (Survival) VOUT Voltage (Survival) IOUT Current (Survival) Junction Temperature Absolute Maximum Ratings (Note 1) LP38858 Symbol Parameter Conditions MIN TYP MAX VIN = VOUT(NOM) + 1V, f = 120 Hz - 80 - VIN = VOUT(NOM) + 1V, f = 1 kHz - 65 - VBIAS = VOUT(NOM) + 3V, f = 120 Hz - 58 - VBIAS = VOUT(NOM) + 3V, f = 1 kHz - 58 - Output Noise Density f = 120 Hz - 1 - Output Noise Voltage VOUT = 1.8V BW = 10 Hz − 100 kHz - 150 - BW = 300 Hz − 300 kHz - 90 - Thermal Shutdown Junction Temperature - 160 - Thermal Shutdown Hysteresis - 10 - Units AC Parameters PSRR (VIN) PSRR (VBIAS) en Ripple Rejection for VIN Input Voltage Ripple Rejection for VBIAS Voltage dB µV/√Hz µVRMS Thermal Parameters TSD TSD(HYS) θJ-A θJ-C Thermal Resistance, Junction to Ambient(Note 3) TO220-5 - 60 - TO263-5 - 60 - Thermal Resistance, Junction to Case(Note 3) TO220-5 - 3 - TO263-5 - 3 - °C °C/W Note 1: Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but does not guarantee specific performance limits. For guaranteed specifications and conditions, see the Electrical Characteristics. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Test method is per JESD22-A114. The HBM rating for device pin 1 (SS) is ±1.5 kV. Note 3: Device power dissipation must be de-rated based on device power dissipation (PD), ambient temperature (TA), and package junction to ambient thermal resistance (θJA). Additional heat-sinking may be required to ensure that the device junction temperature (TJ) does not exceed the maximum operating rating. See the Application Information section for details. Note 4: Output voltage line regulation is defined as the change in output voltage from nominal value resulting from a change in input voltage. Note 5: Output voltage load regulation is defined as the change in output voltage from nominal value as the load current increases from no load to full load. Note 6: Dropout voltage is defined the as input to output voltage differential (VIN - VOUT) where the input voltage is low enough to cause the output voltage to drop 2% from the nominal value. www.national.com 4 VBIAS Ground Pin Current (IGND(BIAS)) vs VBIAS VBIAS Ground Pin Current (IGND(BIAS)) vs Temperature 20202787 20202761 VIN Ground Pin Current vs Temperature Load Regulation vs Temperature 20202762 20202763 Dropout Voltage (VDO) vs Temperature Output Current Limit (ISC) vs Temperature 20202765 20202766 5 www.national.com LP38858 Typical Performance Characteristics Unless otherwise specified: TJ = 25°C, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, IOUT = 10 mA, CIN = COUT = 10 µF Ceramic, CBIAS = 1 µF Ceramic, CSS = open. LP38858 VOUT vs Temperature UVLO Thresholds vs Temperature 20202768 20202767 Soft-Start Resistor (rSS) vs Temperature Soft-Start rSS Variation vs Temperature 20202774 20202775 VOUT vs CSS, 10 nF to 47 nF VIN Line Transient Response 20202776 www.national.com 20202777 6 LP38858 VIN Line Transient Response VBIAS Line Transient Response 20202778 20202779 VBIAS Line Transient Response Load Transient Response, COUT = 10 µF Ceramic 20202780 20202781 Load Transient Response, COUT = 10 µF Ceramic Load Transient Response, COUT = 100 µF Ceramic 20202782 20202783 7 www.national.com LP38858 Load Transient Response, COUT = 100 µF Ceramic Load Transient Response, COUT = 100 µF Tantalum 20202784 20202785 Load Transient Response, COUT = 100 µF Tantalum VBIAS PSRR 20202786 20202770 VIN PSRR Output Noise 20202771 www.national.com 20202769 8 LP38858 Block Diagram 20202705 9 www.national.com LP38858 SUPPLY SEQUENCING There is no requirement for the order that VIN or VBIAS are applied or removed. One practical limitation is that the Soft-Start circuit starts charging CSS when VBIAS rises above the UVLO threshold. If the application of VIN is delayed beyond this point the benefits of Soft-Start will be compromised. In any case, the output voltage cannot be guaranteed until both VIN and VBIAS are within the range of guaranteed operating values. If used in a dual-supply system where the regulator output load is returned to a negative supply, the output pin must be diode clamped to ground. A Schottky diode is recommended for this diode clamp. Application Information EXTERNAL CAPACITORS To assure regulator stability, input and output capacitors are required as shown in the Typical Application Circuit. Output Capacitor A minimum output capacitance of 10 µF, ceramic, is required for stability. The amount of output capacitance can be increased without limit. The output capacitor must be located less than 1 cm from the output pin of the IC and returned to the device ground pin with a clean analog ground. Only high quality ceramic types such as X5R or X7R should be used, as the Z5U and Y5F types do not provide sufficient capacitance over temperature. Tantalum capacitors will also provide stable operation across the entire operating temperature range. However, the effects of ESR may provide variations in the output voltage during fast load transients. Using the minimum recommended 10 µF ceramic capacitor at the output will allow unlimited capacitance, Tantalum and/or Aluminum, to be added in parallel. REVERSE VOLTAGE A reverse voltage condition will exist when the voltage at the output pin is higher than the voltage at the input pin. Typically this will happen when VIN is abruptly taken low and COUT continues to hold a sufficient charge such that the input to output voltage becomes reversed. The NMOS pass element, by design, contains no body diode. This means that, as long as the gate of the pass element is not driven, there will not be any reverse current flow through the pass element during a reverse voltage event. The gate of the pass element is not driven when VBIAS is below the UVLO threshold. When VBIAS is above the UVLO threshold the control circuitry is active and will attempt to regulate the output voltage. Since the input voltage is less than the output voltage the control circuit will drive the gate of the pass element to the full VBIAS potential when the output voltage begins to fall. In this condition, reverse current will flow from the output pin to the input pin , limited only by the RDS(ON) of the pass element and the output to input voltage differential. Discharging an output capacitor up to 1000 μF in this manner will not damage the device as the current will decay rapidly. However, continuous reverse current should be avoided. Input Capacitor The input capacitor must be at least 10 µF, but can be increased without limit. It's purpose is to provide a low source impedance for the regulator input. A ceramic capacitor, X5R or X7R, is recommended. Tantalum capacitors may also be used at the input pin. There is no specific ESR limitation on the input capacitor (the lower, the better). Aluminum electrolytic capacitors can be used, but are not recommended as their ESR increases very quickly at cold temperatures. They are not recommended for any application where the ambient temperature falls below 0°C. Bias Capacitor The capacitor on the bias pin must be at least 1 µF, and can be any good quality capacitor (ceramic is recommended). INPUT VOLTAGE The input voltage (VIN) is the high current external voltage rail that will be regulated down to a lower voltage, which is applied to the load. The input voltage must be at least VOUT + VDO, and no higher than whatever values is used for VBIAS. SOFT-START The LP38858 incorporates a Soft-Start function that reduces the start-up current surge into the output capacitor (COUT) by allowing VOUT to rise slowly to the final value. This is accomplished by controlling VREF at the SS pin. The soft-start timing capacitor (CSS) is internally held to ground until VBIAS rises above the Under-Voltage Lock-Out threshold (ULVO). VREF will rise at an RC rate defined by the internal resistance of the SS pin (rSS), and the external capacitor connected to the SS pin. This allows the output voltage to rise in a controlled manner until steady-state regulation is achieved. Typically, five time constants are recommended to assure that the output voltage is sufficiently close to the final steady-state value. During the soft-start time the output current can rise to the built-in current limit. BIAS VOLTAGE The bias voltage (V BIAS) is a low current external voltage rail required to bias the control circuitry and provide gate drive for the N-FET pass transistor. The bias voltage must be in the range of 3.0V to 5.5V to ensure proper operation of the device. UNDER VOLTAGE LOCKOUT The bias voltage is monitored by a circuit which prevents the device from functioning when the bias voltage is below the Under-Voltage Lock-Out (UVLO) threshold of approximately 2.45V. As the bias voltage rises above the UVLO threshold the device control circuitry becomes active. There is approximately 150 mV of hysteresis built into the UVLO threshold to provide noise immunity. When the bias voltage is between the UVLO threshold and the Minimum Operating Rating value of 3.0V the device will be functional, but the operating parameters will not be within the guaranteed limits. www.national.com Soft-Start Time = CSS × rSS × 5 (1) Since the VOUT rise will be exponential, not linear, the in-rush current will peak during the first time constant (τ), and VOUT will require four additional time constants (4τ) to reach the final value (5τ) . After achieving normal operation, should VBIAS fall below the ULVO threshold the device output will be disabled and the Soft-Start capacitor (CSS) discharge circuit will become active. The CSS discharge circuit will remain active until VBIAS 10 The second part is the power that is dissipated in the bias and control circuitry, and can be determined with the formula: PD(BIAS) = VBIAS × IGND(BIAS) (3) where IGND(BIAS) is the portion of the operating ground current of the device that is related to VBIAS. The third part is the power that is dissipated in portions of the output stage circuitry, and can be determined with the formula: PD(IN) = VIN × IGND(IN) (4) where IGND(IN) is the portion of the operating ground current of the device that is related to VIN. The total power dissipation is then: PD = PD(PASS) + PD(BIAS) + PD(IN) (5) The maximum allowable junction temperature rise (ΔTJ) depends on the maximum anticipated ambient temperature (TA) for the application, and the maximum allowable operating junction temperature (TJ(MAX)) . (6) The maximum allowable value for junction to ambient Thermal Resistance, θJA, can be calculated using the formula: (7) Heat-Sinking The TO-220 Package The TO220-5 package has a θJA rating of 60°C/W and a θJC rating of 3°C/W. These ratings are for the package only, no additional heat-sinking, and with no airflow. If the needed θJA, as calculated above, is greater than or equal to 60°C/W then no additional heat-sinking is required since the package can safely dissipate the heat and not exceed the operating TJ(MAX). If the needed θJA is less than 60°C/W then additional heat-sinking is needed. The thermal resistance of a TO-220 package can be reduced by attaching it to a heat sink or a copper plane on a PC board. If a copper plane is to be used, the values of θJA will be same as shown in next section for TO-263 package. The heat-sink to be used in the application should have a heat-sink to ambient thermal resistance, θHA: 20202723 FIGURE 1. Typical CSS vs COUT Values The CSS capacitor must be connected to a clean ground path back to the device ground pin. No components, other than CSS, should be connected to the SS pin, as there could be adverse effects to VOUT. If the Soft-Start function is not needed the SS pin should be left open, although some minimal capacitance value is always recommended. POWER DISSIPATION AND HEAT-SINKING Additional copper area for heat-sinking may be required depending on the maximum device dissipation (PD) and the maximum anticipated ambient temperature (TA) for the device. Under all possible conditions, the junction temperature must be within the range specified under operating conditions. The total power dissipation of the device is the sum of three different points of dissipation in the device. The first part is the power that is dissipated in the NMOS pass element, and can be determined with the formula: (8) where θJA is the required total thermal resistance from the junction to the ambient air, θCH is the thermal resistance from the case to the surface of the heart-sink, and θJC is the thermal resistance from the junction to the surface of the case. For this equation, θJC is about 3°C/W for a TO-220 package. The value for θCH depends on method of attachment, insulator, etc. θCH varies between 1.5°C/W to 2.5°C/W. Consult the heat-sink manufacturer datasheet for details and recommendations. PD(PASS) = (VIN - VOUT) × IOUT (2) 11 www.national.com LP38858 falls to 500 mV (typical). When VBIAS falls below 500 mV (typical), the CSS discharge circuit will cease to function due to a lack of sufficient biasing to the control circuitry. Since VREF appears on the SS pin, any leakage through CSS will cause VREF to fall, and thus affect VOUT. A leakage of 50 nA (about 10 MΩ) through CSS will cause VOUT to be approximately 0.1% lower than nominal, while a leakage of 500 nA (about 1 MΩ) will cause VOUT to be approximately 1% lower than nominal. Typical ceramic capacitors will have a factor of 10X difference in leakage between 25°C and 85°C, so the maximum ambient temperature must be included in the capacitor selection process. Typical CSS values will be in the range of 1 nF to 100 nF, providing typical Soft-Start times in the range of 70 μs to 7 ms (5τ). Values less than 1 nF can be used, but the Soft-Start effect will be minimal. Values larger than 100 nF will provide soft-start, but may not be fully discharged if VBIAS falls from the UVLO threshold to less than 500 mV in less than 100 µs. Figure 1 shows the relationship between the COUT value and a typical CSS value. LP38858 Figure 2 shows that increasing the copper area beyond 1 square inch produces very little improvement. The minimum value for θJA for the TO-263 package mounted to a PCB is 32°C/W. Figure 3 shows the maximum allowable power dissipation for TO-263 packages for different ambient temperatures, assuming θJA is 35°C/W and the maximum junction temperature is 125°C. Heat-Sinking The TO-263 Package The TO-263 package has a θJA rating of 60°C/W, and a θJC rating of 3°C/W. These ratings are for the package only, no additional heat-sinking, and with no airflow. The TO-263 package uses the copper plane on the PCB as a heat-sink. The tab of this package is soldered to the copper plane for heat sinking. shows a curve for the θJA of TO-263 package for different copper area sizes, using a typical PCB with 1 ounce copper and no solder mask over the copper area for heat-sinking. 20202726 FIGURE 3. Maximum power dissipation vs ambient temperature for the TO-263 package 20202725 FIGURE 2. θJA vs Copper (1 Ounce) Area for the TO-263 package www.national.com 12 LP38858 Physical Dimensions inches (millimeters) unless otherwise noted TO-220 5-Lead, Stagger Bend Package (TO220-5) NS Package Number TO5D TO-263 5-Lead, Molded, Surface Mount Package (TO263-5) NS Package Number TS5B 13 www.national.com LP38858 1.5A Fast-Response High-Accuracy LDO Linear Regulator with Soft-Start Notes THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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