80V, Low Dropout Voltage Linear Regulator

Transcription

1 RT972A/B 8V, Low Dropout Voltage Linear Regulator General Description The RT972A/B is a high voltage (8V operation), low quiescent current, low dropout linear regulator. The device supplies 2mA output current with a maximum dropout voltage of 23mV. Its low quiescent and shutdown currents (23 A operating and 3 A shutdown) are ideal for use in battery-powered and/or high voltage systems. Ground current is well-controlled in all conditions, including dropout. The RT972A/B operates with any reasonable output capacitors including 1 F low-esr ceramic types. It features excellent line and load transient responses. Internal protection circuitry includes reverse-battery protection, current limiting, thermal shutdown, and reverse current protection. Output voltage accuracy is ±3% over the entire line, load, and temperature range. The RT972A/B has an adjustable output voltage (1.25V to 6V). It is available in the SOT-23-5 package. Applications Low Current, High Voltage Regulators Battery Powered Applications Telecom and Datacom Applications Automotive Applications Features Wide Input Voltage Range: 4.5V to 8V Low Quiescent Current : 23 A Operating and 3 A Shutdown Low Dropout Voltage: 18mV (typical) at 2mA Adjustable (1.25V to 6V) Output Voltage 2% Initial Output Tolerance 3% Output Tolerance over Line, Load, Temperature Range Stable with 1 F Output Capacitor Stable with Aluminum, Tantalum or Ceramic Capacitors No Reverse-Current Protection Diode Needed 8V Reverse-Battery Protection Internal Current Limit Internal Thermal Shutdown Protection Marking Information RT972AGB 4Y=DNN RT972BGB 4X=DNN 4Y= : Product Code DNN : Date Code 4X= : Product Code DNN : Date Code Simplified Application Circuit RT972A/B V IN VIN VOUT V OUT C IN R1 C COMP C OUT / GND FB R2 DS972A/B-1 June

2 RT972A/B Ordering Information RT972A/B Note : Richtek products are : Package Type B : SOT-23-5 Lead Plating System G : Green (Halogen Free and Pb Free) A : Low Shutdown B : High Shutdown RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-2. Suitable for use in SnPb or Pb-free soldering processes. Pin Configurations (TOP VIEW) VOUT 5 FB VIN GND / SOT-23-5 Functional Pin Description Pin No. Pin Name Pin Function 1 VIN 2 GND Ground. 3 4 FB (RT972B) (RT972A) 5 VOUT Power Input. Bypass VIN with a.18 F or larger capacitor with adequate voltage rating. Shutdown Control Input. Connect of RT972B high to disable the output voltage and reduce the IC s quiescent current to 3 A (typical). Connect low to enable the output. is a high-voltage pin and can be connected directly to a high-voltage input less than 6V. Shutdown Control Input. Connect of RT972A low to disable the output voltage and reduce the IC s quiescent current to 3 A (typical). Connect high to enable the output. is a high-voltage pin and can be connected directly to a high-voltage input less than 6V. Feedback Voltage Input. Connect to the center tap of a resistor divider for setting the output voltage. Output Voltage Pin. The VOUT pin supplies power to the load. A minimum output capacitor of 1 F is required for stable operation. DS972A/B-1 June 216 2

3 RT972A/B Function Block Diagram VIN VOUT / - + VREF Current Limit Over- Temperature Protection FB GND Operation The RT972A/B is a high input-voltage linear regulator specifically designed to minimize external components. The input voltage range is from 4.5V to 8V. The device supplies 2mA of output current with a maximum dropout voltage of 23mV. Its 23 A quiescent and 3 A shutdown currents make it ideal for use in battery-powered applications. Unlike many PNP LDO regulators, ground current does not increase much in dropout conditions. Output Transistor The RT972A/B includes a built-in PNP output transistor configured for low dropout voltage. The output transistor blocks reverse current from output to input node if the output voltage is held higher than the input voltage (such as in battery-backup applications). Error Amplifier The Error Amplifier compares the output feedback voltage at FB to an internal reference voltage and controls the PNP output transistor's base current to maintain output voltage regulation. Current Limit Protection The RT972A/B provides a current limit function to prevent damage during output over-load or shorted-circuit conditions. The output current is detected by an internal current-sense transistor. Over-Temperature Protection The over-temperature protection function will turn off the PNP output transistor when the internal junction temperature exceeds 15 C (typ.). Once the junction temperature cools down by approximately 2 C, the regulator will automatically resume operation. Reverse-Battery Protection The RT972A/B VIN can withstand reverse voltages as high as 8V. Both the IC and the load are protected and no negative voltage will appear at the output. Reverse-Output Protection The RT972A/B protects against current flow to the input (VIN) when the output voltage exceeds VIN. If the input is left open circuit or grounded, the FB pin will act like a resistor (typically 1k) in series with a diode when pulled above ground. If the FB pin is connected to a resistor divider now and the output voltage is held higher than the input voltage, a current will conduct from output via the resistor divider and FB node to ground. Because the current is limited by the resistor divider and FB internal resistor, no additional output blocking diode is needed if the limited current is acceptable. DS972A/B-1 June

4 RT972A/B Shutdown Control The RT972B input is an active-high input that turns off the output transistor and reduces the quiescent current to 3 A typical. Connect to a voltage below.4v for normal operation. The RT972A input is an active-low input that turns off the output transistor and reduces the quiescent current to 3 A typical. Connect to a voltage above 2V for normal operation. DS972A/B-1 June 216 4

5 Absolute Maximum Ratings (Note 1) RT972A/B VIN Pin Voltage V to 9V / Pin Voltage V to 6V VOUT to GND Voltage V to 8V VOUT to VIN Voltage V to 8V FB Pin Voltage V to 7V Power Dissipation, TA = 25 C SOT W Package Thermal Resistance (Note 2) SOT-23-5, JA C/W Lead Temperature (Soldering, 1 sec.) C Junction Temperature C Storage Temperature Range C to 15 C ESD Susceptibility (Note 3) HBM (Human Body Model) kV MM (Machine Model) V Recommended Operating Conditions (Note 4) Supply Input Voltage V to 8V Ambient Temperature Range C to 85 C Junction Temperature Range C to 125 C Electrical Characteristics (4.5V < V IN < 8V, V = 2V (RT972A), V = V (RT972B), FB pin connected to VOUT pin, C OUT = 1 F (ceramic), T A = 25 C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Input Voltage VIN ILOAD = 2mA V FB Pin Voltage VFB VIN = 12V, ILOAD = 1 A A < ILOAD < 2mA V Line Regulation VLINE VIN = 4.5V to 8V, ILOAD = 1 A mv Load Regulation VLOAD VIN = 12V, ILOAD = 1 A to 2mA mv ILOAD = 1 A Dropout Voltage VDROP ILOAD = 1mA ILOAD = 1mA mv ILOAD = 2mA GND Pin Current IGND ILOAD = ma ILOAD = 2mA A Output Voltage Noise VON COUT = 1 F, ILOAD = 2mA, BW = 1Hz to 1kHz VRMS FB Pin Bias Current IFB na DS972A/B-1 June

6 RT972A/B Parameter Symbol Test Conditions Min Typ Max Unit Shutdown Threshold VIH VIL RT972A Off to On; RT972B On to Off RT972A On to Off; RT972B Off to On V / Pin Current I I V/V = V --.1 V/V = 2V A Quiescent Current in Shutdown ISD VIN = 6V, V = 2V or V = V A Power Supply Rejection Rate PSRR VIN = 7V (Avg), VRIPPLE =.5 VP-P, fripple = 12Hz, ILOAD = 2mA db Output Current Limit ILIM VIN = 12V, VOUT = 11V, VFB = 1.2V ma Input Reverse Leakage Current Reverse Output Current Over-Temperature Protection IVINr VIN = 8V, VOUT = V ma IVOUTr FB connect to OUT, VOUT = 1.27V, VIN < V A TSD C Note 1. Stresses beyond those listed Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. JA is measured at T A = 25 C on a high effective thermal conductivity four-layer test board per JEDEC JC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions. DS972A/B-1 June 216 6

7 Typical Application Circuit RT972A/B V IN 4.5V to 8V C IN.18μF VIN / RT972A/B VOUT FB R1 R2 C COMP C OUT 1μF V OUT 1.25V to 6V GND Figure 1. RT972A/B Adjustable Output V IN 4.5V to 8V VIN RT972A/B VOUT MJD31C C IN.18μF / GND FB R3 1 R1 R2 C COMP C OUT 1μF V OUT 1.25V to 6V Figure 2. RT972A/B External Transistor Application DS972A/B-1 June

8 PSRR (db) Shutdown Current (μa) Output Voltage (%) Quiescent Current (µa) Output Voltage (%) Quiescent Current (μa) RT972A/B Typical Operating Characteristics.4 Output Voltage vs. Load Current 3 Quiescent Current vs. Supply Voltage V IN = 12V V OUT = 3.3V Load Current (ma) Supply Voltage (V).5 Output Voltage vs. Temperature 4 Quiescent Current vs. Temperature V IN = 4.5V V IN = 8V I OUT =.1mA 1 5 V IN = 12V Temperature ( ) Temperature ( C) PSRR vs. Frequency 1 Shutdown Current vs. Supply Voltage -1-2 C OUT =.47μF C OUT = 4.7μF Frequency (Hz) Supply Voltage (V) DS972A/B-1 June 216 8

9 Dropout Voltage (mv) Reverse Current (μa) Current Limit (ma) Output Voltage (%) RT972A/B 8 Current Limit vs. Supply Voltage.1 Output Voltage vs. Supply Voltage I OUT = ma I OUT =.1mA I OUT = 1mA I OUT = 2mA Supply Voltage (V) Supply Voltage (V) 1 Ground Current vs. Supply Voltage 12 Reverse Current vs. Temperature Ground Current (μa) I OUT = ma I OUT =.1mA I OUT = 1mA I OUT = 1mA I OUT = 2mA Supply Voltage (V) V IN = -8V Temperature ( ) Dropout Voltage vs. Temperature I OUT =.1mA I OUT = 1mA I OUT = 1mA I OUT = 2mA +8V VOUT vs. VIN I OUT = 2mA C OUT = 1μF 15 V IN (3V/Div) 1 5 V OUT (2V/Div) -8V Temperature ( ) Time (1msec/Div) DS972A/B-1 June

10 RT972A/B Line Transient Waveform Falling Line Transient Waveform Rising V OUT (1V/Div) I OUT = 2mA C OUT = 1μF C COMP = 22pF V OUT (1V/Div) I OUT = 2mA C OUT = 1μF C COMP = 22pF V OUT_AC (1mV/Div) V OUT_AC (1mV/Div) Time (25μsec/Div) Time (25μsec/Div) Line Transient Waveform Full Load Transient Waveform V OUT (1V/Div) V OUT_AC (1mV/Div) I OUT = 2mA C OUT = 1μF C COMP = 22pF I OUT (1mA/Div) V OUT_AC (2mV/Div) V IN = 12V V OUT = 3.3V I OUT = 2mA C OUT = 1μF C COMP = 22pF Time (5μsec/Div) Time (5μsec/Div) DS972A/B-1 June 216 1

11 RT972A/B Application Information The RT972A/B is a high input-voltage linear regulator specifically designed to minimize external components. The input voltage range is from 4.5V to 8V. The device supplies 2mA of output current with a maximum dropout voltage of 23mV. Adjustable Output Voltage and Compensation The adjustable output may be set to provide from 1.25V to 8V, using external feedback voltage divider resistors (Figure 1). To achieve the correct compensation (with your external FB divider, use a lower divider resistor (R2) value below 1k. Calculate R1 according to the following formula : R2 = R1 / (VOUT / 1.25V 1). Then, calculate the compensation capacitor (CCOMP) value according to the following formula : CCOMP = 25 s/r1 Added External NPN for High-Current Applications Higher output currents and/or increased power dissipation are possible using an external NPN output transistor. VOUT drives the base of the transistor and FB monitors the actual output voltage, as in normal applications. The output (Figure 2) can be used. Component Selection A low-esr capacitor such as ceramic type must be connected between VIN and GND with short, wide traces to bypass input noise. RT972A/B is designed to work with small input capacitor to reduce the cost from high-voltage low-esr requirement. To guarantee a minimum.1 F input capacitance, a ceramic.18 F input capacitor with an appropriate voltage rating is recommended. The RT972A/B operates with any reasonable output capacitor including low-esr ceramic types. Low-ESR aluminum and tantalum capacitor may also be used. A minimum of 1 F is recommended and much higher values are also acceptable. Connect the output capacitor between VOUT and GND with short, wide traces to keep the circuit stable. Thermal Considerations The RT972A/B s high input-voltage capability and high output current capability require careful use to avoid over-heating the IC and activating the internal thermal protection. To avoid thermal shutdown, do not exceed the IC s maximum operating junction temperature range of 125 C. For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) TA) / JA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and JA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125 C. The junction to ambient thermal resistance, JA, is layout dependent. For SOT-23-5 package, the thermal resistance, JA, is C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25 C can be calculated by the following formula : PD(MAX) = (125 C 25 C) / (218.1 C/W) =.45W for SOT-23-5 package The maximum power dissipation depends on the operating ambient temperature for fixed TJ(MAX) and thermal resistance, JA. The derating curve in Figure 3 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. DS972A/B-1 June

12 RT972A/B Maximum Power Dissipation (W) Four-Layer PCB C OUT VOUT R2 R1 GND VOUT FB C COMP VIN GND / Figure 4. PCB Layout Guide C IN GND Ambient Temperature ( C) Figure 3. Derating Curve of Maximum Power Dissipation DS972A/B-1 June

13 RT972A/B Outline Dimension Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A A B b C D e H L SOT-23-5 Surface Mount Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1 st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863) Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS972A/B-1 June