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MAX5033BUPA Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX5033BUPA Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 17 page 500mA, 76V, High-Efficiency, MAXPower Step-Down DC-DC Converter _______________________________________________________________________________________ 9 Detailed Description The MAX5033 step-down DC-DC converter operates from a 7.5V to 76V input voltage range. A unique volt- age-mode control scheme with voltage feed-forward and an internal switching DMOS FET provides high effi- ciency over a wide input voltage range. This pulse- width modulated converter operates at a fixed 125kHz switching frequency. The device also features automat- ic pulse-skipping mode to provide low quiescent cur- rent and high efficiency at light loads. Under no load, the MAX5033 consumes only 270µA, and in shutdown mode, consumes only 10µA. The MAX5033 also fea- tures undervoltage lockout, hiccup-mode output short- circuit protection, and thermal shutdown. Shutdown Mode Drive ON/OFF to ground to shut down the MAX5033. Shutdown forces the internal power MOSFET off, turns off all internal circuitry, and reduces the VIN supply cur- rent to 10µA (typ). The ON/OFF rising threshold is 1.69V (typ). Before any operation begins, the voltage at ON/OFF must exceed 1.69V (typ). The ON/OFF input has 100mV hysteresis. Undervoltage Lockout (UVLO) Use the ON/OFF function to program the UVLO thresh- old at the input. Connect a resistive voltage-divider from VIN to GND with the center node to ON/OFF as shown in Figure 1. Calculate the threshold value by using the following formula: The minimum recommended VUVLO(TH) is 6.5V, 7.5V, and 13V for the output voltages of 3.3V, 5V, and 12V, respectively. The recommended value for R2 is less than 1M Ω. If the external UVLO threshold-setting divider is not used, an internal undervoltage-lockout feature monitors the supply voltage at VIN and allows operation to start when VIN rises above 5.2V (typ). This feature can be used only when VIN rise time is faster than 2ms. For slower VIN rise time, use the resistive divider at ON/OFF. Boost High-Side Gate Drive (BST) Connect a flying bootstrap capacitor between LX and BST to provide the gate-drive voltage to the high-side n-channel DMOS switch. The capacitor is alternately charged from the internally regulated output-voltage VD and placed across the high-side DMOS driver. Use a 0.1µF, 16V ceramic capacitor located as close to the device as possible. On startup, an internal low-side switch connects LX to ground and charges the BST capacitor to VD. Once the BST capacitor is charged, the internal low-side switch is turned off and the BST capacitor voltage provides the necessary enhancement voltage to turn on the high-side switch. Thermal-Overload Protection The MAX5033 features integrated thermal-overload protection. Thermal-overload protection limits total power dissipation in the device, and protects the device in the event of a fault condition. When the die temperature exceeds +160°C, an internal thermal sen- sor signals the shutdown logic, turning off the internal power MOSFET and allowing the IC to cool. The ther- mal sensor turns the internal power MOSFET back on after the IC’s die temperature cools down to +140°C, resulting in a pulsed output under continuous thermal- overload conditions. Applications Information Setting the Output Voltage The MAX5033A/B/C have preset output voltages of 3.3V, 5.0V, and 12V, respectively. Connect FB to the preset output voltage (see the Typical Operating Circuit). The MAX5033D offers an adjustable output voltage. Set the output voltage with a resistive voltage-divider con- nected from the circuit’s output to ground (Figure 1). Connect the center node of the divider to FB. Choose R4 less than 15k Ω, then calculate R3 as follows: R V R OUT 3 122 122 4 = − × (. ) . V R R V UVLO TH () . =+ × 1 1 2 185 MAX5033D GND BST LX VIN SGND FB D1 50SQ100 VD 220 µH VOUT 5V, 0.5A VIN 7.5V TO 76V 47 µF 0.1 µF 0.1 µF COUT 33 µF R1 R2 R3 41.2k Ω R4 13.3k Ω ON/OFF Figure 1. Adjustable Output Voltage |
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