DS8008-07 RICHTEK | Alldatasheet
Document overview
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Technical content
Features
zzzzz 2.5V to 5.5V Input Range zzzzz Adjustable Output From 0.6V to VIN Adjustable Output Voltage zzzzz 600mA Output Current, 1A Peak Current zzzzz 95% Efficiency zzzzz No Schottky Diode Required zzzzz 1.5MHz Fixed Frequency PWM Operation zzzzz Small SOT-23-5 and TSOT-23-5 Package zzzzz RoHS Compliant and 100% Lead (Pb)-Free
Applications
z Personal Information Appliances z Wireless and DSL Modems z MP3 Players z Portable Instruments 1.5MHz, 600mA, High Efficiency PWM Step-Down DC/DC Converter General Description The RT8008 is a high-efficiency pulse-width-modulated (PWM) step-down DC/DC converter. Capable of delivering 600mA output current over a wide input voltage range from 2.5V to 5.5V, the RT8008 is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery or from other power sources within the range such as cellular phones, PDAs and handy-terminals. Internal synchronous rectifier with low R DS(ON) dramatically reduces conduction loss at PWM mode. No external Schottky diode is required in practical application. The RT8008 automatically turns off the synchronous rectifier while the inductor current is low and enters discontinuous PWM mode. This can increase efficiency at light load condition. The RT8008 enters Low-Dropout mode when normal PWM cannot provide regulated output voltage by continuously turning on the upper P-MOSFET. RT8008 enter shutdown mode and consumes less than 0.1μA when EN pin is pulled low. The switching ripple is easily smoothed-out by small package filtering elements due to a fixed operation frequency of 1.5MHz. This along with small SOT-23-5 and TSOT-23-5 package provides small PCB area application. Other features include soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection.
Ordering Information
(TOP VIEW) SOT-23-5/TSOT-23-5 EN GND LX FB/VOUT VIN Note : Richtek products are : \ RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. \ Suitable for use in SnPb or Pb-free soldering processes. RT8008(- ) Package Type B : SOT-23-5 J5 : TSOT-23-5 Output Voltage Default : Adjustable 10 : 1.0V 12 : 1.2V 15 : 1.5V 18 : 1.8V 25 : 2.5V 33 : 3.3V Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area.
DS8008-07 March 2011 www.richtek.com Functional Pin Description Pin Number Pin Name Pin Function 1 EN Chip Enable (Active High, do not leave EN pin floating, and V EN < VIN + 0.6V). 2 GND Ground. 3 LX Pin for Switching. 4 VIN Power Input. 5 FB/VOUT Feedback Input Pin. Function Block Diagram COMP RC RS1 RS2 EN VIN LX FB/VOUT UVLO & Power Good Detector VREF Slope Compensation Current Sense OSC & Shutdown Control Zero Detector Current Limit Detector DriverControl LogicPWM ComparatorError Amplifier GND
DS8008-07 March 2011www.richtek.com Absolute Maximum Ratings (Note 1) z Power Dissipation, PD @ TA = 25°C z Package Thermal Resistance (Note 2) z ESD Susceptibility (Note 3)
Electrical Characteristics
Parameter Symbol Test Conditions Min Typ Max Unit Input Voltage Range VIN 2.5 -- 5.5 V Quiescent Current IQ I OUT = 0mA, VFB = VREF + 5% -- 50 100 μA Shutdown Current ISHDN EN = GND -- 0.1 1 μA Reference Voltage VREF For adjustable output voltage 0.588 0.6 0.612 V Adjustable Output Range VOUT VREF -- VIN − 0.2 V ΔVOU T VIN = 2.2 to 5.5V, VOU T = 1.0V 0A < IOUT < 600mA −3 -- 3 % ΔVOU T VIN = 2.2 to 5.5V, VOU T = 1.2V 0A < IOUT < 600mA −3 -- 3 % ΔVOU T VIN = 2.2 to 5.5V, VOU T = 1.5V 0A < IOUT < 600mA −3 -- 3 % ΔVOU T VIN = 2.2 to 5.5V, VOU T = 1.8V 0A < IOUT < 600mA −3 -- 3 % ΔVOU T VIN = 2.8 to 5.5V, VOU T = 2.5V 0A < IOUT < 600mA −3 -- 3 % Fix ΔVOU T VIN = 3.5 to 5.5V, VOU T = 3.3V 0A < IOUT < 600mA −3 -- 3 % VIN = VOUT + 0.2V to 5.5V, VIN ≧ 3.5V 0A < IOUT < 600mA −3 -- 3 % Output Voltage Accuracy Adjustable ΔVOU T VIN = VOUT + 0.4V to 5.5V, VIN ≧ 2.2V 0A < IOUT < 600mA −3 -- 3 % To be continued Recommended Operating Conditions (Note 4)
DS8008-07 March 2011 www.richtek.com Parameter Symbol Test Conditions Min Typ Max Unit FB Input Current IFB VFB = VIN −50 -- 50 nA PMOSFET RON P RDS(ON) IOUT = 200mA Ω NMOSFET RON N RDS(ON) IOUT = 200mA Ω P-Channel Current Limit IP(LM) VIN = 2.5V to 5.5 V 1 -- 1.8 A EN High-Level Input Voltage VENH V IN = 2.5V to 5.5V 1.5 -- -- V EN Low-Level Input Voltage VENL V IN = 2.5V to 5.5V -- -- 0.4 V Under Voltage Lockout Threshold -- 1.8 -- V Hysteresis -- 0.1 -- V Oscillator Frequency fOSC V IN = 3.6V, IOUT = 100mA 1.2 1.5 1.8 MHz Thermal Shutdown Temperature TSD -- 160 -- °C Min. On Time -- 50 -- ns Max. Duty Cycle 100 -- -- % LX Leakage Current V IN = 3.6V, VLX = 0V or VLX = 3.6V −1 -- 1 μA Note 1. Stresses listed as the above “ Absolute Maximum Ratings” may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. θ JA is measured in the natural convection at T A = 25°C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Pin 2 of SOT-23-5/TSOT-23-5 packages is the case position for θJC measurement. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions.
DS8008-07 March 2011www.richtek.com Typical Operating Characteristics Efficiency vs. Load Current 100 Load Current (A) Efficiency (%) VIN = 5V VIN = 3.3V VOUT = 1.2V Efficiency vs. Input Voltage 100 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Efficiency (%) VOUT = 1.2V IOUT = 300mA IOUT = 600mA Current Limit vs. Input Voltage 0.0 0.5 1.0 1.5 2.0 2.5 2 . 533 . 544 . 555 . 5 Input Voltage (V) Current Limit (A) VOUT = 1.2V Frequency vs. Input Voltage 1.35 1.38 1.40 1.43 1.45 1.48 1.50 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Frequency (MHz) VOUT = 1.2V, IOUT = 300mA Frequency vs. Temperature 1.35 1.38 1.40 1.43 1.45 1.48 1.50 -50 -25 0 25 50 75 100 125 Temperature Frequency (MHz) (°C) VOUT = 1.2V, IOUT = 300mA Output Voltage vs. Load Current 1.180 1.185 1.190 1.195 1.200 1.205 1.210 1.215 1.220 Load Current (A) Output Voltage (V) VIN = 5V VIN = 3.3V VOUT = 1.2V VIN = 2.5V
DS8008-07 March 2011 www.richtek.com Reference Voltage vs. Input Voltage 0.5990 0.5995 0.6000 0.6005 0.6010 2 . 533 . 544 . 555 . 5 Input Voltage (V) Reference Voltage (V) VOUT = 1.2V Load Transient Response Time (50 μs/Div) IOUT (500mA/Div) VOUT (20mV/Div) VIN = 3.3V, VOUT = 1.2V, IOUT = 300mA to 600mA Load Transient Response Time (50 μs/Div) IOUT (500mA/Div) VOUT (20mV/Div) VIN = 3.3V, VOUT = 1.2V, IOUT = 200mA to 600mA Output Ripple Time (500ns/Div) ILX (500mA/Div) VLX (5V/Div) VIN = 3.3V, VOUT = 1.2V, IOUT = 600mA VOUT (5mV/Div) Power On Time (100 μs/Div) IIN (200mA/Div) VOUT (500mV/Div) VIN = 3.3V, VOUT = 1.2V, IOUT = 600mA VEN (2V/Div) Output Voltage vs. Temperature 1.15 1.17 1.19 1.21 1.23 1.25 -50 -25 0 25 50 75 100 125 Temperature (°C) Output Voltage (V) VIN = 3.3V, IOUT = 0A
DS8008-07 March 2011www.richtek.com Power Off Time (100 μs/Div) IIN (200mA/Div) VOUT (500mV/Div) VIN = 3.3V, VOUT = 1.2V, IOUT = 600mA VEN (2V/Div)
DS8008-07 March 2011 www.richtek.com Applications Information The basic RT8008 application circuit is shown in Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by C IN and COUT. Inductor Selection For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current ΔI L increases with higher VIN and decreases with higher inductance. Having a lower ripple current reduces the ESR losses in the output capacitors and the output voltage ripple. Highest efficiency operation is achieved at low frequency with small ripple current. This, however, requires a large inductor. A reasonable starting point for selecting the ripple current is ΔI L = 0.4(IMAX). The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation : Inductor Core Selection Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite or mollypermalloy cores. Actual core loss is independent of core size for a fixed inductor value but it is very dependent on the inductance selected. As the inductance increases, core losses decrease. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “ hard” , which means that inductance collapses abruptly when the peak design ⎡ −⎥⎦ IN OUTOUTL V V1Lf VΔI ⎡ −⎥⎦ Δ×= IN(MAX) OUT L(MAX) OUT V V1If VL current is exceeded. This results in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate! Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don ’ t radiate energy but generally cost more than powdered iron core inductors with similar characteristics. The choice of which style inductor to use mainly depends on the price vs size requirements and any radiated field/EMI requirements. C IN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used. RMS current is given by : V V VII OUT IN IN OUT OUT(MAX)RMS −= This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. The selection of C OUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients, as well as the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, ΔV OUT, is determined by : ⎡ +≤ OUT LOUT 8fC 1ESR ΔIΔV The output ripple is highest at maximum input voltage since ΔIL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special
of the output voltage as shown in Figure 4. Figure 4. Setting the Output Voltage actual power lost is of no consequence.
- The VIN quiescent current is due to two components :
be more pronounced at higher supply voltages.
- I2R losses are calculated from the resistances of the
high voltage coefficient and audible piezoelectric effects. can also lead to significant ringing.
DS8008-07 March 2011 www.richtek.com Outline Dimension A e b B D C H L SOT-23-5 Surface Mount Package Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.889 1.295 0.035 0.051 A1 0.000 0.152 0.000 0.006 B 1.397 1.803 0.055 0.071 b 0.356 0.559 0.014 0.022 C 2.591 2.997 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024
DS8008-07 March 2011www.richtek.com Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the ri ght to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property inf ringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications i s assumed by Richtek. Richtek Technology Corporation Taipei Office (Marketing) 5F, No. 95, Minchiuan Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)86672399 Fax: (8862)86672377 Email: marketing@richtek.com TSOT-23-5 Surface Mount Package Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 C 2.591 3.000 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 A e b B D C H L