Triple-Output TFT-LCD DC-DC Converters

Active: In Production.

The MAX1748/MAX8726 triple-output DC-DC converters in a low-profile TSSOP package provide the regulated voltages required by active-matrix, thin-film transistor (TFT) liquid-crystal displays (LCDs). One high-power DC-DC converter and two low-power charge pumps convert the +3.3V to +5V input supply voltage into three independent output voltages.

The primary 1MHz DC-DC converter generates a boosted output voltage (V_MAIN) up to 13V using ultra-small inductors and ceramic capacitors. The low-power BiCMOS control circuitry and the low on-resistance (0.35Ω) of the integrated power MOSFET allows efficiency up to 93%.

The dual charge pumps independently regulate one positive output (V_POS) and one negative output (V_NEG). These low-power outputs use external diode and capacitor stages (as many stages as required) to regulate output voltages up to +40V and down to -40V. A proprietary regulation algorithm minimizes output ripple, as well as capacitor sizes for both charge pumps.

For both the MAX1748 and MAX8726, the supply sequence is V_MAIN first, V_NEG next, and finally V_POS. The MAX1748 soft-starts each supply as soon as the previous supply finishes. The MAX8726 adds a delay between the startups of V_MAIN and V_NEG and also between V_NEG and V_POS.

The MAX1748/MAX8726 are available in the ultra-thin TSSOP package (1.1mm max height).

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