Pololu 2868 - 2.5-9V Fine-Adjust Step-Up/Step-Down Voltage Regulator w/ Adjustable Low-Voltage Cutoff S9V11MACMA

Overview:

The S9V11x family of efficient switching regulators (also called switched-mode power supplies (SMPS) or DC-to-DC converters) use 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, offering a typical efficiency of over 85% and a typical output current of up to 1.5 A. The flexibility in input voltage offered by this family of regulators is especially well-suited for battery-powered applications in which the battery voltage begins above the regulated voltage and drops below as the battery discharges. Without the typical restriction on the battery voltage staying above the required voltage throughout its life, new battery packs and form factors can be considered.

The different members of this family offer different output voltage options, from fixed voltages with selectable alternatives to adjustable voltages that can be set anywhere between 2.5 V and 9 V using a precision 12-turn potentiometer. Some versions also have an adjustable low-voltage cutoff that can be set anywhere in the 2 V to 16 V output voltage range and used 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.

Details for item #2868These regulators have short-circuit protection, and thermal shutdown prevents damage from overheating; they do not have reverse-voltage protection. 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 Typical efficiency and output current section below).

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 (precision-adjustable using built-in 12-turn potentiometer)
• Typical maximum continuous output current: 1.5 A (when input voltage is close to the output; the Typical efficiency and output current section below shows how the achievable continuous output current depends on the input and output voltages)
• Precision-adjustable low-voltage cutoff with hysteresis can be used to protect batteries from over-discharging (quiescent current is approximately 10 µA per volt on VIN when regulator is disabled)
• Power-good indicator can be used to tell when the regulator has reached and is maintaining its target output voltage
• Power-saving feature maintains high efficiency at low currents (quiescent current is less than 1 mA while enabled)
• Integrated over-temperature and short-circuit protection
• Small size: 0.5″ × 0.6″ × 0.25″ (12.7 × 15.3 × 6.4 mm)

Using the Regulator:

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

Connections:

The step-up/step-down regulator has five main connections all located along the same edge of the board: the output voltage (OUT), ground (GND), the input voltage (IN), an enable input (EN), and a power good indicator (PG). The board also contains a through-hole labeled SEL that is not used on this version of the regulator.

The output voltage, VOUT, is determined by the trimmer potentiometer position. See the Setting the output voltage section below for details.

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

The regulator features an enable pin, EN, that can be used as a precision low-voltage cutoff thanks to its tight activation and deactivation thresholds (voltages below 0.7 V trigger a low-power sleep state, and voltages above 0.8 V re-enable the regulator). On this regulator version, EN is connected to VIN through a 12-turn potentiometer to provide a user-adjustable cutoff threshold, which is useful for battery powered applications where draining the battery below a particular voltage threshold could permanently damage it. The quiescent current draw in this sleep mode is dominated by the current in the resistor network from ENABLE to VIN, which is approximately 10 µA per volt on VIN (e.g. approximately 30 µA with 3 V in). See the Setting the cutoff voltage section below for details on how to use the built-in potentiometer to set the cutoff threshold.

The “power good” indicator, PG, is an open-drain output that goes low when the regulator’s output falls below around 90% of the nominal voltage, including when the enable pin is held low. The power good indicator is held low until the output reaches 95% of the nominal voltage when it is powering up or coming out of low-power mode. Otherwise, the PG pin is high-impedance, so an external pull-up resistor is required to use this pin.

Included hardware:

The through-holes are arranged with a 0.1″ spacing along the edge of the board for compatibility with standard solderless breadboards and perfboards and connectors that use a 0.1″ grid. You can solder wires directly to the board or solder in pieces of the included breakaway 6×1 straight male header strip or the 5×1 right-angle male header strip as desired.

Setting the output voltage:

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. While this is not likely to damage the regulator, it might not work reliably or its output could become unstable when the output voltage is not within 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.

Setting the cutoff voltage:

The low VIN cutoff voltage of the regulator is controlled by adjusting the voltage at the EN pin with a 12-turn precision potentiometer. When the voltage on the EN pin falls below 0.7 V the regulator is put in a low-power sleep state and when the voltage on EN rises back above 0.8 V the regulator is turned back on. Turning the potentiometer clockwise increases the low-voltage cutoff. The cutoff voltage can be set by measuring the voltage on the VIN and EN pins and using the potentiometer to adjust the voltage on EN according to the following equation:

Solving for EN yields approximately 0.86 V, so you should turn the potentiometer until you measure that voltage on the EN pin.

Note that the regulator’s low VIN cutoff behavior includes hysteresis: the regulator turns off when EN falls below 0.7 V, but it does not turn back on until EN rises above 0.8 V. Therefore, VIN must reach about 114% of the cutoff voltage before the regulator will re-enable its output (about 3.43 V in this example).

Typical efficiency and output current:

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. As shown in the graphs below, this family of switching regulators typically has an efficiency of 85% to 95%. A power-saving feature maintains these high efficiencies even when the regulator current is very low.

The maximum achievable output current of these regulators varies with the input voltage but also depends on other factors, including the ambient temperature, air flow, and heat sinking. The graph below shows maximum output currents that these regulators can deliver continuously at room temperature in still air and without additional heat sinking. Depending on the input and output voltage, these regulators can temporarily deliver over 2 A, though they will typically quickly overheat under such conditions and go into thermal shutdown.

Note that the startup current for input voltages above the regulated output voltage is limited to approximately 700 mA, and currents in excess of this are only available after the output has finished stabilizing. For input voltages below the output voltage, the available start up current decreases linearly with the input voltage to approximately 0.3 A with an input of 3 V. Large capacitive loads will generally not pose a problem because they will gradually charge up even with the current limit active, so while they may increase the time it takes an S9V11x family regulator to start up, the regulator should still eventually stabilize. A purely resistive load, however, could prevent the regulator from ever reaching the desired output voltage. For example, if the output of the regulator is 5V and 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, the voltage at which the current draw reaches the 700 mA limit. As such, this family of regulators is intended for applications like robotics, where any large loads are controllable and can be applied only after the regulator has finished starting up.

LC Voltage Spikes:

When connecting voltage to electronic circuits, the initial rush of current can cause voltage spikes that are much higher than the input voltage. If these spikes exceed a regulator’s maximum voltage, the regulator can be destroyed. If you are connecting more than about 9 V, using power leads more than a few inches long, or using a power supply with high inductance, we recommend soldering a 33 μF or larger electrolytic capacitor close to the regulator between VIN and GND. The capacitor should be rated for at least 20 V.

Dimensions:

General specifications:

Identifying markings:

Notes:

1 Without included optional headers.

2 Note: the minimum startup voltage is 3V, but the regulator can operate down to 2V after startup.

3 Under typical conditions, where the input voltage is close to the output voltage. Maximum output current can be higher when stepping down and lower when stepping up.

4 Output voltage is set by a built-in precision 12-turn potentiometer.

5 With no load. Actual quiescent current depends on input voltage; it is typically under 300 µA when the input voltage is close to the output voltage.