MAX1729

19-1406; Rev 1; 1/99 KIT ATION EVALU SHEET A T A WS D FOLLO ECB and LCD Display Bias Supply with Accurate Output Voltage and Temperature Compensation General Description The MAX1729 micropower step-up/step-down DC-DC converter is ideally suited for electrically controlled birefringence (ECB) and liquid-crystal-display (LCD) biassupply generation. It provides step-up/step-down voltage conversion and reduces output ripple by using a step-up DC-DC converter followed by a linear regulator. This architecture permits a physically smaller inductor than those used in competing SEPIC and flyback topologies. This device features low quiescent current (67µA typical). A logic-controlled shutdown mode further reduces quiescent current to 0.4µA typical. The MAX1729 features an input that dynamically adjusts the output voltage to control display color or contrast. It offers two feedback modes: internal and external. Internal feedback mode allows output voltages between 2.5V and 16V, and is specifically designed to hold temperature drift to ±11ppm/°C. External feedback mode allows the MAX1729 output voltage range to be tailored for various displays. An on-chip temperature sensor with a positive temperature coefficient provides compensation for LCD/ECB display temperature characteristics. In internal feedback mode, the buffered temperature sensor output is read and used to adjust the output voltage via a digital control signal. External feedback mode features an additional compensation meth...