LP3990 – A Positive Voltage Regulator

For most of our applications, we use the power taken from power lines. Usually, this power has disturbances and errors. This poses a challenge for the device that needs a constant value of uninterrupted power supply for their proper functioning. This is where the regulators like LP3990 come into the picture. These are voltage regulators. These devices help in providing a regulated output voltage supply when the input power is distorting. They are available for both DC and AC power.

What is LP3990?

Voltage regulators are devices used to give a regulated output voltage for the proper working of the devices. Some of the devices may get damaged if the voltage given to them as input is fluctuating and if it rises above the recommended value.

Voltage regulators are a must to such type of circuits. Voltage regulators use a feedback differential amplifier to regulate the output. One of such positive voltage regulator is LP3990.

LP3990 is a low noise, low quiescent current positive voltage regulator. This is specially designed for Digital applications. This is designed to be stable with space-saving small ceramic capacitors of 1µF. Thermal protection and shutdown circuitry is provided.

With fast start-up and accurate output, it meets the needs of portable, battery-powered digital systems. Single input and single output capacitors are required for stability. This device is capable of providing a small output of 0.8V when an input of 2V is given and a load current of about 150mA. Its power consumption is reduced to virtually zero when switched into shutdown mode.

Block Diagram

The block diagram of IC LP990 is shown below.



The enable pin of LP3990 is internally held low with the help of a 1M resistor to ground. A voltage higher than the given threshold voltage is needed to ensure that the device is fully enabled. The output of the device gets disabled if the enable pin is left open.

Thermal Overload Protection

When the junction temperature of the device rises above 1550C, the output of the device gets disabled by the thermal protection circuit. When the temperature falls below 1400C, the output gets enabled. The thermal protection circuit gets activated based on the values of power dissipation, thermal resistance and ambient temperature.

Block diagram of LP3990
Block diagram of LP3990

How To Use?

While using LP3990 for our application certain specifications should be checked. Such as the available input voltage range of the IC, Output voltage needed for the application, output current needed, input and output capacitors.

Circuit Diagram of LP3990
Circuit Diagram of LP3990

Design requirements for a typical application for LP3990 are as follows-

  • Input voltage range – 2V to 6V.
  • Output voltage- 1.8V.
  •  Typical Output current – 100mA.
  •  Output capacitor range – 1µF

Input Capacitor

L3990 requires an input capacitor for stability. An Input capacitor of 1µF is connected between Input and Ground.

Output Capacitor

For stability, the output capacitor should be of recommended range -1µF and also ESR value in the range of 5mΩ to 500mΩ. This capacitor should be connected from the output pin to ground.

Pin Configuration

LP3990 is available in three types of packages. 4 Pin DSBGA, 5 Pin SOT-23, 6 Pin WSON package.

Pin Diagram of LP3990
Pin Diagram of LP3990

The Pin Configuration of DSBGA-

  •  Pin A1 is the common ground GND.
  • Pin A2 is the enable input pin EN. When the voltage at this pin is greater than or equal to 0.95V, the regulator is enabled. When the voltage is less than or equal to 0.4V, the regulator gets disabled. This pi has a 1M pull-down resistor to ground.
  • B1 is the output pin OUT. This pin is connected to the load circuit. An external capacitor has to be connected to this pin.
  •  B2 is the input pin IN. a 1µF capacitor should be connected to the input pin.

The Pin Configuration of SOT-23 Package –

  • Pin-1 is the input pin IN.
  • Pin-2 is the common ground GND.
  • Pin-3 is Enable input EN.
  • Pin-4 doesn’t have any internal connection.
  • Pin-5 is the output pin OUT.

The Pin Configuration of WSON package-

  • Pin-1 is the voltage output OUT.
  • Pin-2 is the common ground GND.
  • Pin-3  doesn’t have any internal connection.
  •  Pin-4 doesn’t have any internal connection.
  • Pin-5 is the Enable input EN.
  • Pin-6 is the voltage supply input IN.
  • A thermal Pad is connected to the pin-2.


The Specifications of LP3990 are as follows-

  • This device has an input voltage range of 2V to 6V.
  • LP3990 has an output voltage range of 0.8V to 3.3V.
  • This device gives output current of 150mA.
  • This device doesn’t require a noise bypass capacitor.
  • To gain stability ceramic capacitor is used.
  • LP3990 can give 1% voltage accuracy at room temperature.
  • This device has Logic controlled Enable.
  • For stability of output 1 µF external capacitor is required.
  • Fast start-up of about 105µs can be achieved by this device.
  •  This device has a low output noise of 150µVRMS.
  •  LP3990 has very low IQ of about 43µA when enabled.
  • When disabled this device has virtually zero IQ.
  • This device has PSRR of 55dB at 1 kHz.
  • LP3990 has thermal overload and short-circuit protection.
  • This device is designed for Digital applications.
  • Available for output voltages 0.8V, 1.2V, 1.35V, 2.5V, 1.5V, 2.8V, 1.8V and 3.3V.
  • Available in three types of packages.
  • Internal thermal shutdown circuitry protects the device from permanent damage
  •  Junction temperature range is from -400C to 1250C.
  • Maximum Enable voltage is equal to the Input voltage.
  • Storage Temperature range is from -650C to 1500C.


The applications of LP3990 are as follows-

  • Used in portable, battery-powered systems.
  • This device is applied in Cellular Handsets.
  • Hand-held portable systems use this IC.

Alternative IC

Some of the IC that can be used as an alternative to LP3990 is LP5907, TLV1117, TPS795, LP5912, TPS7A90, TPS718XX, TPS719XX, UA78MXX, etc…

Besides positive voltage regulators, there are negative voltage regulators also available. These negative voltage regulators are useful for providing a negative reference voltage. Further electrical characteristics of LP3990 under different temperature conditions can be found in the datasheet provided by the Texas Instrumentations. For which of your application have you preferred LP3990?

Image Credits: Texas Instrumentations