RT8265 RICHTEK | Alldatasheet
Document overview
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Technical content
Features
zzzzz Wide Operating Input Range : 4.75V to 24V zzzzz Adjustable Output Voltage Range : 0.8V to 15V zzzzz Output Current up to 3A zzzzz 25μμμμμA Low Shutdown Current zzzzz Power MOSFET : 110mΩΩΩΩΩ zzzzz High Efficiency up to 93% zzzzz 1MHz Fixed Switching Frequency zzzzz Stable with Low ESR Output Ceramic Capacitors zzzzz Programmable Soft-Start zzzzz Thermal Shutdown zzzzz Cycle-By-Cycle Over Current Protection zzzzz RoHS Compliant and 100% Lead (Pb)-Free Typical Application Circuit Package Type SP : SOP-8 (Exposed Pad-Option 1) RT8265 Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) VIN EN GND BOOT FB SW7 4.7µHCB 10nF 47µF 6.3V 49.9k 16k VOUT 3.3V 10µF/25V Chip Enable VIN 4.75V to 24V RT8265 B330A SS8 CS 0.1µF COMP CC 0.56nF RC 82k CP NC 9 (Exposed Pad)
1 BOOT
2 VIN
Power Switching Output. SW is the switching node that supplies power to the output. required from SW to BS to power the high side switch. for maximum power dissipation. reference voltage is 0.8V typically.
6 COMP
Compensation Node. COMP is used to compensate the regulation control loop. control loop. In some cases, an additional capacitor from COMP to GND is required. will be pulled to high by internal circuit. Table 1. Recommended Component Selection
DS8265-02 March 2011 www.richtek.com Function Block Diagram R QS Q VA Control Logic EA UV Comparator Oscillator 1MHz/150kHz VIN_track 0.64V Internal Regulator 1µA Shutdown Comparator Current Sense Amplifier SS BOOT VIN GND SW FB EN COMP - OC Limit Comparator 0.8V + 15µA VCC 10k VA VCC
DS8265-02 March 2011www.richtek.com
Electrical Characteristics
Parameter Symbol Test Conditions Min Typ Max Unit Feedback Reference Voltage V FB 4.75V ≤ VIN ≤ 24V 0.784 0.8 0.816 V High Side Switch-On Resistance R DS(ON)1 -- 0.11 -- Ω Low Side Switch-On Resistance R DS(ON)2 -- 10 -- Ω Switch Leakage V EN = 0V, VSW = 0V -- -- 10 μA Current Limit I LIM 3.8 5 -- A Oscillator Frequency f SW -- 1 -- MHz Short Circuit Oscillation Frequency -- 100 -- kHz Maximum Duty Cycle -- 85 -- % Minimum On-Time t ON -- 100 -- ns Under Voltage Lockout Threshold Rising 3.8 4.2 4.65 V Under Voltage Lockout Threshold Hysteresis -- 200 -- mV En input Low Voltage -- -- 0.4 V En input High Voltage 1.4 -- -- V Enable Pull Up Current -- 1 3 μA Shutdown Current I SHDN V EN = 0V -- 25 -- μA Quiescent Current I Q V EN = 2V, VFB = 1V -- 0.8 1 mA Soft-Start Period C SS = 0.1μF -- 10 -- ms Thermal Shutdown T SD -- 150 -- °C (VIN = 12V, TA = 25°C unless otherwise specified) Absolute Maximum Ratings (Note 1) z Power Dissipation, PD @ TA = 25°C z Package Thermal Resistance (Note 2) z ESD Susceptibility (Note 3) Recommended Operating Conditions (Note 4)
DS8265-02 March 2011 www.richtek.com 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 high effective four layers thermal conductivity test board of JEDEC 51-7 thermal measurement standard. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions.
DS8265-02 March 2011www.richtek.com Typical Operating Characteristics Output Voltage vs. Output Current 3.10 3.15 3.20 3.25 3.30 3.35 3.40 0 0.5 1 1.5 2 2.5 3 Output Current (A) Output Voltage (V) VIN = 12V VIN = 24V VOUT = 3.3V Efficiency vs. Load Current 100 00 . 6 1 . 2 1 . 8 2 . 43 Load Current (A) Efficiency (%) Efficiency vs. Load Current VIN = 12V VIN = 24V VOUT = 5V Efficiency vs. Load Current 100 0 0.6 1.2 1.8 2.4 3 Load Current (A) Efficiency (%) VIN = 12V VIN = 24V VOUT = 3.3V Efficiency vs. Load Current Reference Voltage vs. Input Voltage 0.770 0.775 0.780 0.785 0.790 0.795 0.800 0.805 0.810 0.815 0.820 4 6.5 9 11.5 14 16.5 19 21.5 24 Input Voltage (V) Reference Voltage (V) VOUT = 3.3V, IOUT = 0A Output Voltage vs. Temperature 3.10 3.16 3.22 3.28 3.34 3.40 -50 -25 0 25 50 75 100 125 Temperature (°C) Output Voltage (V) VIN = 12V, VOUT = 3.3V, IOUT = 0A Shutdown Current vs. Temperature -50 -25 0 25 50 75 100 125 Temperature (°C) Shutdown Current (µA) 1 VIN = 12V, VOUT = 3.3V
DS8265-02 March 2011 www.richtek.com Current Limit vs. Input Voltage 3.00 3.50 4.00 4.50 5.00 5.50 6.00 4 6.5 9 11.5 14 16.5 19 21.5 24 Input Voltage (V) Current Limit (A) Peak Current, VOUT = 3.3V Frequency vs. Input Voltage 0.88 0.90 0.92 0.94 0.96 0.98 1.00 4 6.5 9 11.5 14 16.5 19 21.5 24 Input Voltage (V) Frequency (MHz) VOUT = 3.3V, IOUT = 0.3A Load Transient Response Time (50 μs/Div) IOUT (2A/Div) VOUT (50mV/Div) VIN = 12V, IOUT = 1.5A to 3A Current Limit vs. Temperature 3.0 3.5 4.0 4.5 5.0 5.5 6.0 - 5 0 - 2 50 2 55 07 5 1 0 0 1 2 5 Temperature (°C) Current Limit (A) VIN = 12V VIN = 24V Peak Current, VOUT = 3.3V Frequency vs. Temperature 0.80 0.84 0.88 0.92 0.96 1.00 -50 -25 0 25 50 75 100 125 Temperature (°C) Frequency (MHz) 1 VIN = 12V VIN = 24V VOUT = 3.3V, IOUT = 0.3A Quiescent Current vs. Temperature 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -50 -25 0 25 50 75 100 125 Temperature (°C) Quiescent Current (mA ) VIN = 12V VIN = 24V VOUT = 3.3V VIN = 5.5V
DS8265-02 March 2011www.richtek.com Power On from EN Time (2.5ms/Div) VOUT (2V/Div) IIN (500mA/Div) VIN = 12V, IOUT = 3A VEN (5V/Div) Power Off from EN Time (250 μs/Div) VOUT (2V/Div) IIN (500mA/Div) VIN = 12V, IOUT = 3A VEN (5V/Div) Load Transient Response Time (50 μs/Div) IOUT (2A/Div) VOUT (50mV/Div) VIN = 24V, IOUT = 1.5A to 3A Switching Time (500ns/Div) VLX (10V/Div) ILX (2A/Div) VIN = 12V, IOUT = 3A VOUT (10mV/Div)
DS8265-02 March 2011www.richtek.com Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. The previous situation 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 do not radiate energy. However, they are usually more expensive than the similar powdered iron inductors. The rule for inductor choice mainly depends on the price vs. size requirement and any radiated field/EMI requirements. Diode Selection When the power switch turns off, the path for the current is through the diode connected between the switch output and ground. This forward biased diode must have a minimum voltage drop and recovery times. Schottky diode is recommended and it should be able to handle those current. The reverse voltage rating of the diode should be greater than the maximum input voltage, and current rating should be greater than the maximum load current. For more detail please refer to Table 3. CIN and COUT Selection The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the high side MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : This formula has a maximum at V IN = 2V OUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. 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. For the input capacitor, a 10 μF low ESR ceramic capacitor is recommended. For the recommended capacitor, please refer to table 2 for more detail. The input capacitor has to connect another 10μF ceramic capacitor between the input and ground when the input voltage is lower than 6.5V. The selection of COUT is determined by the required ESR to minimize voltage ripple. Moreover, the amount of bulk capacitance is also a key for COUT selection 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 : The output ripple will be highest at the 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 requirement. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR value. However, it provides lower capacitance density than other types. Although Tantalum capacitors have the highest capacitance density, it is important to only use types that pass the surge test for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR. However, it can be used in cost-sensitive applications for ripple current rating and long term reliability considerations. Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing. Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, V IN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at V IN large enough to damage the part. OUT INRMS OUT(MAX) IN OUT V VI = I 1 VV − OUT L OUT 1V I ESR 8fC
would indicate a stability problem. θJA is the junction to ambient thermal resistance. the standard JEDEC 51-7 four-layers thermal test board. temperature on the maximum power allowed. \` Connect feedback network behind the output capacitors. behind the output capacitors. Figure 3. Derating Curves for RT8265 Packages
Table 2. Suggested Capacitors for CIN and COUT Table 1. Suggested Inductors for Typical Application Circuit Table 3. Suggested Diode as close to the IC as possible. components away from this trace. as close to the device as possible.
DS8265-02 March 2011 www.richtek.com Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 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 Outline Dimension A BJ F H M C D I Y X EXPOSED THERMAL PAD (Bottom of Package) 8-Lead SOP (Exposed Pad) Plastic Package Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 4.000 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.510 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.000 0.152 0.000 0.006 J 5.791 6.200 0.228 0.244 M 0.406 1.270 0.016 0.050 X 2.000 2.300 0.079 0.091 Option 1 Y 2.000 2.300 0.079 0.091 X 2.100 2.500 0.083 0.098 Option 2 Y 3.000 3.500 0.118 0.138