Overview
A single-cell lithium-ion battery typically has a voltage range of 3.0 V to 4.2 V. Cell capacity varies by model (for example, 3700 mAh or 4500 mAh), but the cell voltage range remains the same: the fully charged voltage must not exceed 4.2 V, and the discharged voltage should not drop below 3.0 V.
When a project is powered by a single-cell battery but other circuitry requires a stable 5.0 V supply, the solution is to design a DC-DC boost converter that accepts the 3.0 V–4.2 V input range and outputs a regulated 5.0 V. In battery-powered designs, low quiescent current is important: lower static consumption extends battery life, while higher static consumption shortens it. The MT3608 DC-DC boost regulator meets these requirements for many single-cell applications.
MT3608: Basic Specifications
According to the MT3608 datasheet, the input voltage range is 2.0 V to 24 V, which covers the single-cell lithium-ion range. The device can regulate its output up to 28 V, making a 5.0 V output feasible. Quiescent current can be as low as 0.1 μA (100 nA), meeting tight standby-power requirements for battery applications.
Application Circuit and Operation
The MT3608 uses a negative-feedback network to set the output voltage, so the output is adjustable rather than fixed. The regulation equation is:
Vout = Vref * (1 + R1 / R2)
Where Vref is the internal reference voltage (0.6 V), and R1 and R2 are the feedback resistors. For a target output of 5.0 V and R2 = 10 kΩ, R1 should be approximately 73.3 kΩ.
Relevant pins and functions:
- VIN: power input, connected to the single-cell battery.
- SW: switching node, used in the boost conversion topology.
- EN: enable pin. A logic high enables output regulation; a logic low disables the device and places it in low-power shutdown.
The inductor L1 and the Schottky diode D1 are essential components of the boost topology and cannot be omitted. The MT3608 can supply up to 2 A output current, which is generally sufficient for many single-cell powered applications.
Conclusion
This example shows a straightforward approach to convert a single-cell lithium-ion voltage (3.0 V–4.2 V) to a stable 5.0 V supply using the MT3608 boost regulator while keeping quiescent current to a minimum. The design highlights adjusting the feedback network to achieve the required output and ensuring necessary external components are included for reliable boost operation.
