QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 697 HIGH CURRENT QUAD OUTPUT SWITCHING REGULATOR FOR 5V INPUT TFT-LCD PANELS LT1943 DESCRIPTION Demonstration Circuit 697 is a quad output power All four switchers are synchronized to the internal supply intended for use in large TFT-LCD panels. The 1.2MHz clock, allowing the use of low profile induc- circuit features the LT1943 high current quad-output tors and ceramic capacitors. They all have soft-start switching regulator and generates a 3.3V logic supply to limit inrush current. along with the triple output supply required for the Long wires run from input sources (such as wall TFT-LCD panels. With an input voltage range of 4.5V adaptors) can cause large voltage spikes during initial to 8V, a step down regulator provides 3.3V V with LOGIC plug-in. C17 is installed on DC697 to damp the pos- up to 1.5A current a high power boost converter, a sible voltage spikes. C17 is not required for applica- lower power boost converter and an inverting con- tions where input source is close to the regulator. verter provide three independent output voltages Please refer to Application Note 88 for details. AV , V and V required by the LCD panels. An in- DD ON OFF Design files for this circuit board are available. Call ternal high side PNP provides delayed turn on of the the LTC factory. V signal. ON LT is a trademark of Linear Technology Corporation Table 1. Performance Summary (T = 25C unless otherwise noted) A PARAMETER CONDITION VALUE Minimum Input Voltage -40C to 85C 4.5V Maximum Input Voltage -40C to 85C 8V Output Voltage V V = 4.5V to 8V, I = 0A to 1.5A 3.3V 3% LOGIC IN OUT Maximum Output Current at V V = 4.5V to 8V 1.5A LOGIC IN Typical Output Ripple V V = 5V, load at V = 1.5A (20MHz BW) 19mV LOGIC IN LOGIC PP Typical Output Ripple AV V = 5V, load at AV = 500mA (20MHz BW) 33mV DD IN DD PP Typical Switching Frequency 1.2MHz Logic Low Voltage-Off, -40C to 85C 0.4V MAX On/Off Control Logic High Voltage-On 2.4V MIN QUICK START PROCEDURE Demonstration circuit 697 is easy to set up to evalu- minals. See Figure 2 for proper scope probe tech- ate the performance of the LT1943. Refer to Figure 1 nique. for proper measurement equipment setup and follow 1. With power off, connect the input power supply to the procedure below: Vin and GND. NOTE: When measuring the input or output voltage 2. Set the input between 4.5V to 8V. Turn on the ripple, care must be taken to avoid a long ground lead power at the input. on the oscilloscope probe. Measure the input or out- put voltage ripple by touching the probe tip directly across the input or one of the outputs and GND ter- 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 697 HIGH CURRENT QUAD OUTPUT SWITCHING REGULATOR FOR 5V INPUT TFT-LCD PANELS 3. Check for the proper output voltages. If there is no serve the output voltage regulation, ripple voltage, output, temporarily disconnect the load to make efficiency and other parameters. sure that the load is not set too high. 4. Once the proper output voltages are established, NOTE: If more than 20mA is needed at V , connect ON adjust the loads within the operating range and ob- L3 to a higher input, such as AV . DD Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2