Datasheet MAX5035 (Maxim) - 10

MAX5035
1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Detailed Description
On startup, an internal low-side switch connects LX to ground and charges the BST capacitor to VD. Once the The MAX5035 step-down DC-DC converter operates BST capacitor is charged, the internal low-side switch from a 7.5V to 76V input voltage range. A unique volt- is turned off and the BST capacitor voltage provides age-mode control scheme with voltage feed-forward the necessary enhancement voltage to turn on the and an internal switching DMOS FET provides high effi- high-side switch. ciency over a wide input voltage range. This pulse- width modulated converter operates at a fixed 125kHz
Thermal-Overload Protection
switching frequency. The device also features automat- The MAX5035 features integrated thermal overload pro- ic pulse-skipping mode to provide low quiescent cur- tection. Thermal overload protection limits total power rent and high efficiency at light loads. Under no load, dissipation in the device, and protects the device in the the MAX5035 consumes only 270µA, and in shutdown event of a fault condition. When the die temperature mode, consumes only 10µA. The MAX5035 also fea- exceeds +160°C, an internal thermal sensor signals the tures undervoltage lockout, hiccup mode output short- shutdown logic, turning off the internal power MOSFET circuit protection, and thermal shutdown. and allowing the IC to cool. The thermal sensor turns the internal power MOSFET back on after the IC’s die tem-
Shutdown Mode
perature cools down to +140°C, resulting in a pulsed Drive ON/OFF to ground to shut down the MAX5035. output under continuous thermal overload conditions. Shutdown forces the internal power MOSFET off, turns off all internal circuitry, and reduces the VIN supply cur-
Applications Information
rent to 10µA (typ). The ON/OFF rising threshold is 1.69V (typ). Before any operation begins, the voltage at
Setting the Output Voltage
ON/OFF must exceed 1.69V (typ). The ON/OFF input The MAX5035A/B/C have preset output voltages of 3.3V, has 100mV hysteresis. 5.0V, and 12V, respectively. Connect FB to the preset output voltage (see the Typical Operating Circuit).
Undervoltage Lockout (UVLO)
The MAX5035D/E versions offer an adjustable output Use the ON/OFF function to program the UVLO thresh- voltage. Set the output voltage with a resistive voltage- old at the input. Connect a resistive voltage-divider divider connected from the circuit’s output to ground from VIN to GND with the center node to ON/OFF as (Figure 1). Connect the center node of the divider to shown in Figure 1. Calculate the threshold value by FB. Choose R4 less than 15kΩ, then calculate R3 as using the following formula: follows: ⎛ R1 ⎞ V = 1 + 1 85V V ( UVLO(TH) . − 1.22) ⎝⎜ R2 ⎠⎟ × R OUT 3 = × R4 1.22 The minimum recommended VUVLO(TH) is 6.5V, 7.5V, and 13V for the output voltages of 3.3V, 5V, and 12V, respec- tively. The recommended value for R2 is less than 1MΩ. VIN If the external UVLO threshold-setting divider is not 7.5V TO 76V used, an internal undervoltage-lockout feature monitors 68µF the supply voltage at VIN and allows operation to start VOUT 100µH 5V when VIN rises above 5.2V (typ). This feature can be VIN R1 LX used only when VIN rise time is faster than 2ms. For 0.1µF COUT slower VIN rise time, use the resistive-divider at ON/OFF D1 BST 68µF 50SQ100 ON/OFF. R3 R2
Boost High-Side Gate Drive (BST)
MAX5035D 41.2kΩ Connect a flying bootstrap capacitor between LX and FB BST to provide the gate-drive voltage to the high-side VD R4 N-channel DMOS switch. The capacitor is alternately SGND GND 0.1µF 13.3kΩ 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. Figure 1. Adjustable Output Voltage 10 Maxim Integrated