“Last time we introduced a specially designed 1.5A ultra-low dropout linear regulator RT9048A. It has a soft-start feature that can vary with the input voltage and will not flow from the output to the The current at the input end is different. This time we will introduce an ultra-low dropout linear regulator with a load capacity of only 500mA. Its model is RT9081D. The input voltage range is 0.8V~5.5V. The PCB footprint is only The 1.2mm X 1.2mm = 1.44mm2 ZADFN-6L package is very suitable for portable Electronic products with small space and low voltage.
Author: Richtek Technology
Last time we introduced a specially designed 1.5A ultra-low dropout linear regulator RT9048A. It has a soft-start feature that can vary with the input voltage and will not flow from the output to the The input current is different. This time we will introduce an ultra-low dropout linear regulator with a load capacity of only 500mA. Its model is RT9081D. The input voltage range is 0.8V~5.5V. The PCB footprint is only The 1.2mm X 1.2mm = 1.44mm2 ZADFN-6L package is very suitable for portable electronic products with small space and low voltage.
This is the package pin layout diagram of RT9081D. This layout is very convenient for its PCB design. The following figure is a schematic diagram for reference.
The second pin ADJ/IC of RT9081D can be used in two ways, corresponding to the two setting methods of its output voltage, one is internally fixed, and the output voltage range is set from 0.90V to 1.80V; The other is set by an external resistor divider, which can get any output voltage from 0.8V to 3.6V. These two different output voltage setting methods correspond to two different application circuits:
The lowest input voltage of RT9081D can reach 0.8V. To get a stable output at such a low voltage, a relatively high voltage must be used to drive the gate of its regulator, so there is an external bias voltage input Terminal BIAS, the input voltage range of this terminal is 2.4V~5.5V. Since the regulator tube of RT9081D is N-MOSFET, in order to ensure its maximum conduction, BIAS input voltage VBIAS should be higher than the output voltage by more than 1.6V.
Since the driving power of RT9081D comes from the BIAS terminal, when it is not carrying a load, the current flowing into the IC from its VIN terminal is negligible. Users who are concerned about the quiescent current consumption should look for it from the BIAS terminal, but the specification does not give it. The data in this specific state is only given that its current consumption under operating conditions is 80µA (typical value), and the typical value after shutdown is 0.5µA.
Using the driving voltage applied by BIAS, RT9081D’s pass tube can be fully turned on. The typical value of its minimum on-resistance is 280mΩ, and the maximum value will not exceed 500mΩ. This is because its input and output minimum pressure difference under 500mA full load is typical The value is 140mV and the maximum value is 250mV. These indicators are given at a temperature of 25℃. If the actual temperature is higher or lower, the corresponding data will change. The designer can change the value shown in the figure above. The data is taken into consideration for certain adjustments.
RT9081D has an output voltage accuracy of 1.5% in the full input voltage range and full load range (at 25°C). From the reference voltage and temperature curve shown in the figure above, it can be seen that its reference voltage is between -40°C and 125°C. The maximum deviation from its center value within ℃ is less than 4mV, and the ratio is 0.5%, which is the basic guarantee that it can maintain the output accuracy.
RT9081D has a high input voltage ripple rejection capability, which is higher than 60dB at 1kHz and higher than 50dB at 1MHz. Its output noise index is also very good. Please refer to the figure below for specific data:
If you want to get the best possible output noise index and ripple suppression capability in your own application, please try to use input and output capacitors with larger capacity and smaller series equivalent resistance, and place them as close to the input as possible. , At the output end, plan the current path at the same time to prevent the introduction of unnecessary interference sources, and avoid problems such as circuit oscillation.
The ZADFN-6L package used in the RT9081D has a power dissipation capability of 0.73W at an ambient temperature of 25°C and a standard double-sided board design. It is much better than our common SOT-23-5 package, but the size is much smaller. It should be a good choice for portable products with limited space.