Demonstration circuit 2757A is a 6A buck-boost DC/DC converter featuring the LT3154, a low noise, low-IQ monolithic buck-boost converter with programmable soft-start.
The DC2757A demo board has four user-selectable operating modes:
- An accurate programmable EN/UVLO pin, which is used to ENABLE the converter (JP1).
- BURST MODE© and External CLK/Fixed Frequency PWM (JP2).
- Programmable Soft-Start (JP3).
- Selectable (2.2MHz) and Adjustable Switching Frequency RT (500kHz to 4MHz) (JP4).
The LT3154 uses average current mode control to simplify voltage loop compensation and provide good line and load transient response.
The DC2757A operates with a 1.8V to 5.5V input voltage range. The demo board has been designed with the output voltage set to 3.3V. The LT3154 incorporates a proprietary low noise switching algorithm which optimizes efficiency with input voltages above, below, or equal to the output voltage and ensures seamless transitions between operating modes.
In PWM mode, the LT3154 can operate with a switching frequency between 500kHz to 4MHz by programming the RT resistor R4. It also has a selectable switching frequency (2.2MHz) to optimize small size with high efficiency operation. The LT3154 can be synchronized to the External CLK provided RT is programmed 25%-50% below the synchronization frequency.
The LT3154 has a Soft-Start feature and can be programmed with the soft-start capacitor C13 (EXT SS). It also has a selectable internal soft-start (INT SS) of 2.2ms.
Figure 2 in the demo manual shows typical demo board efficiency. Figure 3 and Figure 4 show the load step response.
The LT3154 data sheet has detailed information about the operation, specifications, and applications of the part. The data sheet should be read in conjunction with the Quick Start Guide.
