12. Start Up of TPS54426 Device Start Up Relative to Enable TPS54426 Start Up
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Notes de l'éditeur
Welcome to the training module on 4.5V to 18V Input, 4-A Synchronous Step-Down SWIFT™ Converter with Eco-Mode™
This training module will introduce to Synchronous Step-Down SWIFT™ Converter with Eco-Mode .
The TPS5442x series, including TPS54425 and TPS54426, are adaptive on-time D-CAP2™ mode synchronous buck converters. The TPS5442x enables system designers to complete the suite of various end equipment’s power bus regulators with a cost effective, low component count, low standby current solution. The main control loop for the TPS5442x uses the D-CAP2™ mode control which provides a very fast transient response with no external compensation components. The TPS54426’s adaptive on-time control supports seamless transition between PWM mode at higher load conditions and Eco-mode™ operation at light loads. Eco-mode™ allows the TPS54426 to maintain high efficiency during lighter load conditions. Both devices operate from 4.5-V to 18-V VIN input. The output voltage can be programmed between 0.76 to 5.5V.
Here shows the functional block diagram of the TPS54426. The TPS54426 is a single, adaptive on-time D-CAP2™ mode synchronous buck converter requiring a very low external component count. The D-CAP2™ control circuit is optimized for low ESR output capacitors such as POSCAP, SP-CAP or ceramic types and features fast transient response with no external compensation. The switching frequency is internally set at a nominal 700 kHz. The high-side and low-side switching MOSFETs are incorporated inside the TPS54426 package along with the gate drive circuitry.
This page gives information on design parameter of TPS5442x. The output voltage is set with a resistor divider from the output node to the VFB pin. The output filter used with the TPS54426 is an LC circuit (L1 and C8 || C9). The TPS54426 requires an input decoupling capacitor and a bulk capacitor is needed depending on the application. A 0.1 µ F ceramic capacitor must be connected between the VBST to SW pin for proper operation. A 1.0 µ F ceramic capacitor must be connected between the VREG5 to GND pin for proper operation.
The output voltage is set with a resistor divider from the output node to the VFB pin. It is recommended to use 1% tolerance or better divider resistors. To change the output voltage, it is necessary to change the value of resistor R1. Changing the value of R1 can change the output voltage above 0.765V. The value of R1 for a specific output voltage can be calculated using the given equation.
At low frequencies, the overall loop gain is set by the output set-point resistor divider network and the internal gain of the TPS54426. The low frequency phase is 180 degrees. At the output filter pole frequency, the gain rolls off at a -40 dB per decade rate and the phase drops rapidly. The inductor saturation current rating must be greater than the calculated peak current and the RMS or heating current rating must be greater than the calculated RMS current. Use 700 kHz for f SW .
The TPS54426 requires an input decoupling capacitor and a bulk capacitor is needed depending on the application. A ceramic capacitor over 10 uF. is recommended for the decoupling capacitor. An additional 0.1 μF capacitor from pin 14 to ground is recommended to improve the stability of the over-current limit function. The capacitor voltage rating needs to be greater than the maximum input voltage.
This page shows the efficiency and efficiency at light loads for the TPS54426 at an ambient temperature of 25°C.
The TPS54426 responses to load transient and output voltage ripple is shown in this page. The current step is from 500 mA to 1.5 A (25% to 75% of rated load). Total peak-to-peak output voltage variation is also shown . The output current is the rated full load of 2A.
This page shows Evaluation board schematic diagram. The high-side and low-side switching MOSFETs are incorporated inside the TPS54426 package along with the gate drive circuitry. The low drain-to-source on resistance of the MOSFETs allow the TPS54426 to achieve high efficiencies and helps keep the junction temperature low at high output currents. The TPS54426 also has an auto-skip Eco-mode™ to enable higher efficiency at light loads.
This page shows startup sequence of TPS54426 device. The device features an adjustable soft start time and a power good function. The device operates from 4.5-V to 18-V VIN input. The output voltage can be programmed between 0.76 V and 5.5 V.
This page gives application information where TPS5442X device can be used. It can be used in Digital TV power supply, HD blue ray disc player, networking home terminal, digital STB
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