2.5-9V Adjustable Step-Up/Step-Down Voltage Regulator S9V11E2A

The Pololu S9V11E2A is a compact buck-boost switching regulator with a user-adjustable output anywhere from 2.5 V to 9 V, set with an onboard trimmer potentiometer. It accepts input voltages from 2 V to 16 V (3 V is required to start). When the input voltage is close to or above the output voltage, it can deliver a maximum continuous output current of 1.7 A. The board measures 0.43″ × 0.65″ × 0.16″ (10.9 × 16.5 × 4.0 mm).

Startup current is limited to approximately 700 mA until the output voltage reaches the nominal voltage. After startup, the maximum continuous current depends on the input and output voltages and is limited by thermal dissipation. See the output current graph below for more information.

Overview

Step-Up/Step-Down Voltage Regulator S9V11E2x, bottom view with dimensions and a US quarter for size reference.

The S9V11x family of efficient switching regulators (also called switched-mode power supplies (SMPS) or DC-to-DC converters) uses a buck-boost topology to convert both higher and lower input voltages to a regulated output voltage. They take input voltages from 2 V to 16 V and increase or decrease them as necessary. They offer typical efficiencies of 85% to 95% and typical continuous output currents over 1.5 A for input voltages close to or greater than the output voltage. (Note: The minimum start-up voltage is 3 V, but the regulator will operate down to 2 V after startup.)

The flexible input voltage range of this family suits battery-powered applications especially well, where the battery voltage begins above the regulated voltage and drops below it as the battery discharges. Because the battery voltage no longer has to stay above the required voltage throughout its life, new battery packs and form factors can be considered.

These regulators have short-circuit protection, and thermal shutdown prevents damage from overheating. The boards do not have built-in protection against reverse voltage, but reverse-voltage protection modules are available to add that functionality. Note that the startup current is limited to approximately 700 mA until the output voltage reaches the nominal voltage. After startup, the available current is a function of the input voltage (see the maximum continuous output current graph below).

The members of this family offer different output voltage options. Some have fixed voltages, a few of which offer a selectable alternative. Others have adjustable voltages that can be set anywhere between 2.5 V and 9 V. Some versions also have an adjustable low-voltage cutoff that can be set anywhere from 2 V to 16 V to prevent your battery from over-discharging. This is particularly useful for battery chemistries that can be damaged when over-discharged, including Li-ion and LiPo.

Step-Up/Step-Down Voltage Regulator S9V11E2x, bottom view with dimensions and a US quarter for size reference.

Pololu 5V Step-Up/Step-Down Voltage Regulator S9V11F5 next to a US quarter dollar for size reference.

2.5-9V Fine-Adjust Step-Up/Step-Down Voltage Regulator w/ Adjustable Low-Voltage Cutoff S9V11MACMA next to US quarter dollar for size reference.

Details for this version

This item is the S9V11E2A, which outputs a user-adjustable voltage between 2.5 V and 9 V. Its voltage adjustment trim pot distinguishes it from the fixed-output versions of the S9V11E2x.

2.5-9V Adjustable Step-Up/Step-Down Voltage Regulator S9V11E2A.

2.5-9V Adjustable Step-Up/Step-Down Voltage Regulator S9V11E2A.

Step-Up/Step-Down Voltage Regulator S9V11E2x, bottom view.

Features

• Input voltage: 2 V to 16 V (note: this regulator requires 3 V to start, but it can operate down to 2 V after startup)
• Output voltage: 2.5 V to 9 V (adjustable)
• Max continuous output current when input voltage ≥ output voltage: 1.7 A (note: startup current is limited to 700 mA until output voltage reaches the nominal voltage; see the maximum continuous output current graph below for current capabilities across the full input voltage range)
• Low quiescent current: < 0.2 mA for most combinations of input and output voltages (see the quiescent current graph below)
• Enable input can put the board into a low-power state where it typically draws 10 µA per volt on VIN
• Soft-start feature limits inrush current and gradually ramps output voltage
• Integrated over-temperature and short-circuit protection
• Power-saving feature maintains high efficiency at low currents
• Compact size: 0.43″ × 0.65″ × 0.16″ (10.9 × 16.5 × 4.0 mm); see the dimension diagram in the Resources section below for more information

Using the Regulator

Connections

The S9V11E2x step-up/step-down regulator has four main connections: the output voltage (VOUT), ground (GND), the input voltage (VIN) and an enable input (EN).

Pinout of the Adjustable Step-Up/Step-Down Voltage Regulator S9V11E2A.

The input voltage, VIN, should be between 3 V and 16 V when the regulator is first powered. Once the regulator is running, it can continue operating down to 2 V. Lower inputs can shut down the voltage regulator, and higher inputs can destroy the regulator. Make sure that noise on your input is not excessive, and be wary of destructive LC spikes (see the LC voltage spikes section below for more information).

VOUT is the regulated output voltage, which is determined by the trimmer potentiometer position (see the setting the output voltage section below for details). The regulator's soft-start feature gradually ramps up the VOUT voltage on start-up to limit inrush current draw.

The regulator is enabled by default. Reducing the voltage on EN below 0.7 V puts it into a low-power sleep state, and increasing the voltage on EN past 0.8 V brings it out of that state again. In sleep mode, the quiescent current draw is dominated by the current in the 100 kΩ pull-up resistor from EN to VIN. This is approximately 10 µA per volt on VIN (e.g. approximately 30 µA with 3 V in). The tight tolerance of the enable input allows a precise low-VIN cutoff to be set, such as with the output of an external voltage divider powered by VIN. This is useful in battery-powered applications where draining the battery below a particular voltage threshold could permanently damage it.

The four connections are labelled on the back of the PCB and are arranged with a 0.1″ (2.54 mm) spacing along the edge of the board. This makes the board compatible with solderless breadboards, connectors and other prototyping arrangements that use a 0.1″ grid. You can solder wires or 0.1″ header pins directly to the board. Note: header pins are not included with this product, but 1×4 straight male headers and 1×4 right-angle male headers are available separately.

S9V11E2x step-up/step-down voltage regulators, soldered with straight and right-angle headers (not included), on a breadboard.

Setting the output voltage

The output voltage of the regulator is controlled with a trimmer potentiometer. Turning the potentiometer clockwise increases the output voltage.

Output voltage settings for the 2.5-9V Adjustable Step-Up/Step-Down Voltage Regulator S9V11E2A.

Please note that the output voltage can be set below 2.5 V at the low end of the potentiometer's range and above 9 V at the high end. This is not likely to damage the regulator. However, it might not work reliably, or its output could become unstable, when the output voltage is outside the recommended 2.5 V to 9 V range.

The output voltage can be up to 3% higher than normal when there is little or no load on the regulator. The output voltage can also drop depending on the current draw, especially when the regulator is boosting a lower voltage to a higher one (stepping up), although it should remain within 5% of the set voltage.

Typical efficiency

The efficiency of a voltage regulator, defined as (Power out)/(Power in), is an important measure of its performance, especially when battery life or heat are concerns.

Typical efficiency of Step-Up/Step-Down Voltage Regulator S9V11x with VOUT set to 3.3V.

Typical efficiency of Step-Up/Step-Down Voltage Regulator S9V11x with VOUT set to 5V.

Typical efficiency of Step-Up/Step-Down Voltage Regulator S9V11x with VOUT set to 6V.

Typical efficiency of Step-Up/Step-Down Voltage Regulator S9V11x with VOUT set to 7.5V.

Typical efficiency of Step-Up/Step-Down Voltage Regulator S9V11x with VOUT set to 9V.

Maximum continuous output current

The maximum achievable output current of the regulator varies with the input voltage. It also depends on other factors, including the ambient temperature, air flow and heat sinking. The graph below shows the maximum output currents that the regulators in the S9V11x family can deliver continuously at room temperature in still air and without additional heat sinking. (Note: this graph does not apply to the smaller S9V11F5, which has lower output current capabilities due to its more compact PCB; see the graphs on its product page for more information.)

Typical maximum continuous output current of Step-Up/Step-Down Voltage Regulator S9V11x.

Note that the startup current is limited to approximately 700 mA. Currents above this are only available after the output has finished rising to the set output voltage. Large capacitive loads will generally not pose a problem because they will gradually charge up even with the current limit active. They may increase the time the regulator takes to start up, but the regulator should still eventually reach its set output voltage. A purely resistive load, however, could prevent the regulator from ever reaching its set output voltage. For example, with the output set to 5 V, if you put a 5 Ω resistor between VOUT and GND and then apply power to the regulator, the output voltage will never rise past 3.5 V. That is the voltage at which the current draw reaches the 700 mA limit. As such, this regulator is intended for applications like robotics, where any large loads are controllable and can be applied only after the regulator has finished starting up.

During normal operation, this product can get hot enough to burn you. Take care when handling this product or other components connected to it.

Quiescent current

The quiescent current is the current the regulator uses just to power itself. The graph below shows it as a function of the input voltage. The module's EN input can be driven low to put the board into a low-power state where it typically draws 10 µA per volt on VIN.

Typical quiescent current of the Step-Up/Step-Down Voltage Regulator S9V11x.

LC voltage spikes

When voltage is first connected to an electronic circuit, the initial rush of current can cause voltage spikes much higher than the input voltage. If these spikes exceed the regulator's maximum voltage (16 V), the regulator can be destroyed. In Pololu's tests with typical power leads (~30″ (76 cm) test clips), spikes approaching 16 V were observed at input voltages approaching 9 V. Power supplies or leads with high inductance will make these spikes worse. Adding an electrolytic capacitor (33 μF is a good starting point) close to the regulator between VIN and GND helps suppress these spikes.

More information about LC spikes can be found in Pololu's application note, Understanding Destructive LC Voltage Spikes, listed under Resources below.

Resources

• Dimension diagram (305k pdf)
• Understanding Destructive LC Voltage Spikes