|Input Type||VIN (MIN)
The MAX668/MAX669 constant-frequency, pulse-width modulating (PWM), current-mode DC-DC controllers are designed for a wide range of DC-DC conversion applications, including step-up, SEPIC, flyback, and isolated-output configurations. Power levels of 20W or more can be controlled with conversion efficiencies of over 90%. The input voltage range of 1.8V to 28V supports a wide range of battery and AC-powered inputs. An advanced BiCMOS design features low operating current (220μA), adjustable operating frequency (100kHz to 500kHz), soft-start, and a SYNC input, allowing the MAX668/MAX669 oscillator to be locked to an external clock.
The MAX669 is optimized for low input voltages with a guaranteed start-up voltage of 1.8V. It requires bootstrapped operation (IC-powered from boosted output) and supports output voltages of up to 28V. The MAX668 operates with inputs as low as 3V and can be connected in either a bootstrapped or non-bootstrapped (IC-powered
from input supply or other source) configuration. When not bootstrapped, it has no restriction on output voltage. Both ICs are available in an extremely compact 10-pin μMAX® package.
This reference design describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to design a negative input, positive output boost converter using Maxim’s MAX668 current mode controller. The power supply has been built and tested, details of which follow later in this document.