The Pocket Boost Converter is a DC-to-DC Boost Converter which generates a supply voltage of 5 V or 3.3 V from a single-cell alkaline battery (typical, 1.5 V). Output currents can go as high as 75 mA (maintaining 3.3 V output) while using 1xAA battery and discharge it all the way down to 0.9 V.

Texas Instruments' TPS61070 - 90% Efficient PFM/PWM Boost Converter:

The Pocket Boost Converter utilises Texas Instruments' TPS61070[1]. It has a typical start-up voltage specified as 1.1 V (with a worst case start-up voltage of 1.2 V) [since the open-load battery voltage of an almost empty alkaline cell is around 1.1 V]. However, once started, it can operate < 0.9 V. Output voltage is programmed by an external resistive feedback divider. In case of Pocket Step-Up Converter, two different networks of External Resistors are employed so as to choose between 5 V and 3.3 V.

At low load currents the TPS61070 enters the power-save mode to maintain a high efficiency over a wide load current range. Also, to prevent malfunctioning of the converter, an Undervoltage Lockout function shuts down the device if the supply voltage is lower than 0.8 V (which is not possible for a single AA cell). [2]

The TPS61070 works well in most single-cell boost applications. Though in some cases the discharging battery terminal voltage could be lower than the start-up voltage of the device, the battery voltage readily recovers above 1.1 V once the load is disconnected. Therefore, the TPS61070 does not have difficulty starting up again even when the battery energy capacity is minimal at these terminal voltages.

Regardless of battery chemistry - alkaline, nickel cadmium (NiCd), or nickel metal hydride (NiMH), the discharging of a battery in an actual application exhibits constant power discharge rather than a constant current discharge. This shortens battery lifetime at lower voltages when nearing its end of discharge, further reducing the battery voltage (during constant power discharge, the discharge current increases as terminal voltage decreases to supply the same power to the load). However, once the load is disconnected, or the device is shut down, the battery voltage recovers to a higher voltage (typically above 1.1 V). [3] Technical Specifications:

• Minimum Startup Voltage - 1.2 V (Once started, it may operate at 0.9 V)
• Precharge Current required for starting up - 30 mA @ 1.2 V to 135 mA @ 5V - [1] (See Page 13 Figure 22 of datasheet)
• Quiescent Current - 19 µA (typical) - [1] (See Page 8 Figure 9 of datasheet)
• Supports Input voltages from 0.9 V to 4.5 V - (like, one-cell, two-cell, or three-cell alkaline, NiCd or NiMH, or one-cell Li-ion or Li-polymer battery)
• Output Voltage: 3.3 V or 5 V (+/- 1 %) - as selected from the voltage selection switch Output from 1xAA Alkaline cell - 3.3 V @ 75 mA (typical) or, Output from 1x Li Ion cell or 3.3V Power source - 5 V @ 200 mA (typical)
• Output Voltage Ripple: 10 mV Vpp (Theoretical)
• Switching Current: 600 mA (typical)
• Switching Frequency: 1.2 MHz (typical)

Features:

• 90 % Efficiency
• Power-Save Mode for Improved Efficiency at Low Output Power
• Load Disconnect During Shutdown
• Overtemperature Protection
• BreadBoard Compatible

Note:

The Pocket Boost Converter comes with a single-cell AA Battery Holder. However, a battery and BreadBoard are not included. Images shown are for reference purposes only.

References:

[1] TPS61070 datasheet [2] Duracell® MN1500 Coppertop AA Battery Datasheet [3] Application Note - Single-cell Battery Discharge Characteristics Using the TPS61070 Boost Converter