MAX1778

 

Part Number	Replacement	Explanation

Description

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The MAX1778/MAX1880–MAX1885 multiple-output DC-DC converters provide the regulated voltages required by active matrix thin-film transistor (TFT) liquid crystal displays (LCD) in a low-profile TSSOP package. One high-power step-up converter and two low-power charge pumps convert the 2.7V to 5.5V input voltage into three independent output voltages. A built-in linear regulator and VCOM buffer complete the power-supply requirements.

The main step-up converter accurately generates an externally set output voltage up to 13V that can supply the display's row/column drivers. The converter's high switching frequency and current-mode PWM architecture provide fast transient response and allow the use of small low-profile inductors and ceramic capacitors. The low-power BiCMOS control circuitry and internal 14V switch (0.35≈ N-channel MOSFET) enable efficiencies up to 91%.

The dual low-power charge pumps (MAX1778/ MAX1880/MAX1881/MAX1882 only) 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 -40V. A unique control scheme minimizes output ripple as well as capacitor sizes for both charge pumps.

A resistor-programmable, 40mA, low-dropout linear regulator (MAX1778/MAX1881/MAX1883/MAX1884 only) provides preregulation or postregulation for any of the supplies. For higher current applications, an external transistor can be added. Additionally, the VCOM buffer provides a high current output that is ideal for driving the capacitive backplane of TFT LCD panels. The VCOM buffer's output voltage is preset with an internal 50% resistive-divider or can be externally adjusted for other voltages.

The MAX1778/MAX1880–MAX1885 are protected against output undervoltage and thermal overload conditions by a latched fault detection circuit that shuts down the device. All devices are available in the ultra-thin TSSOP package (1.1mm max height).

MAX1778, MAX1880, MAX1881, MAX1882, MAX1883, MAX1884, MAX1885: Typical Operating Circuit Enlarge+

Key Features

• 500kHz/1MHz Current-Mode PWM Step-Up Regulator
  • Up to +13V Main High-Power Output
  • ±1% Accurate
  • High Efficiency (91%)
• Dual Regulated Charge-Pump Outputs (MAX1778/MAX1880–MAX1882 only)
  • Up to +40V Positive Charge-Pump Output
  • Up to -40V Negative Charge-Pump Output
• Low-Dropout 40mA Linear Regulator (MAX1778/MAX1881/MAX1883/MAX1884 only)
  • Up to +15V LDO Input
• Optional Higher Current with External Transistor
• 2.7V to 5.5V Input Supply
• Internal Supply Sequencing and Soft-Start
• Power-Ready Output
• Adjustable Fault-Detection Latch
• Thermal Protection (+160°C)
• 0.1µA Shutdown Current
• 0.7mA IN Quiescent Current
• Ultra-Small External Components
• Thin TSSOP Package (1.1mm max height)

Applications/Uses

• TFT LCD Desktop Monitor Panels
• TFT LCD Notebook Displays