|Manufacturer||RICHTEK TECHNOLOGY CORPORATION|
|Input Voltage Range||2.5 ~ 5.5V|
|Quiescent Current||MAX 70μA|
|Shutdown Current||MAX 1μA|
|Reference Voltage||0.588 ~ 0.612V|
|Adjustable Output Range||MAX 0.2V|
|Output Voltage Accuracy||-3 ~ 3%|
|FB Input Current||-50 ~ 50nA|
|P-Channel Current Limit||MIN 1.4A|
|EN High-Level Input Voltage||MIN 1.5V|
|EN Low-Level Input Voltage||MAX 0.4V|
|Under Voltage Lock Out threshold||TYP 1.8V|
|Oscillator Frequency||1.2 ~ 1.8MHz|
|Thermal Shutdown Temperature||TYP 160°C|
|Max. Duty Cycle||MIN 100%|
|LX Leakage Current||-1 ~ 1μA|
The RT8010/A is a high-efficiency Pulse-Width-Modulated (PWM) step-down DC-DC converter. Capable of delivering 1A output current over a wide input voltage range from 2.5V to 5.5V, the RT8010/A is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery or from other power sources such as cellular phones, PDAs and hand-held devices.
Two operating modes are available including : PWM/Low-Dropout autoswitch and shut-down modes. The Internal synchronous rectifier with low RDS(ON) dramatically reduces conduction loss at PWM mode. No external Schottky diode is required in practical application.
The RT8010/A enters Low-Dropout mode when normal PWM cannot provide regulated output voltage by continuously turning on the upper PMOS. RT8010/A enter shut-down 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 operating frequency of 1.5MHz. This along with small WDFN-6L 2x2 and WQFN-16L 3x3 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.
For marking information, contact our sales representative directly or through a RichTek distributor located in your area, otherwise visit our website for detail.
The basic RT8010/A 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 CIN and COUT.
For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current ΔIL 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 ΔIL = 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 :
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 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.
The input capacitance, CIN, 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 :
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.