MAQ5280: 25mA, 120V, Low IQ, High PSRR LDO - Micrel - #9

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Micrel, Inc. MAQ5280 October 2008 9 M9999-102708-B Functional Description MAQ5280 is a high performance linear regulator which accepts wide input operating range 4.5V to 120V. This allows the use in harsh environments. The input can surge from 0V to 120V within a millisecond. The first stage bypass regulator isolates output from this input by producing an intermediate head voltage which is a inputto- post regulator. This post regulator gives the control to regulate the required output voltage. The output voltage is adjustable from 1.22V to 5V. VIN Pin VIN pin is the supply input pin. A 0.18ìF or larger capacitor with proper voltage rating is recommended for filtering the input voltage variations and noise on the input voltage. This capacitor should be close to the VIN and GND pins. CBYP Pin The Bypass pin is the output of the Bypass regulator and the input of the post regulator. By connecting a capacitor from the CBYP pin-to-GND, a greater stability and a much higher PSRR is achieved. A 10ìF ceramic capacitor is recommended and this significantly decreases VOUT noise and perturbations due to line transients. When the MAQ5280 is enabled, the Bypass pin voltage is regulated at 5.5V. To maintain 5.5V regulation and high PSRR, the VIN must be no lower than 6.5V. For VIN less than 6.5V while in dropout, the PSRR is reduced. EN Pin EN pin is a logic level enable input which turns MAQ5280 on/off. Drive EN pin level high to turn the device ON and drive EN pin low to keep the device in shutdown mode. In shutdown mode the MAQ5280 draws typically 20nA from the input supply. EN pin can withstand 120V, allowing EN always connected to input supply for always-ON operation. ADJ Pin ADJ pin gives the flexibility to set the output voltage to the requirement from 1.22V to 5V. Use a resistor divider from output and connect to ADJ pin, internal reference is typically 1.219V. GND Pin This GND pin provides the ground for all the electrical connections. MAQ5280 has exposed pad underneath the package which should be connected to ground. If this exposed pad is connected to wide ground plane it would improve the thermal performance of MAQ5280. NC Pins There are two NC pins on the package which are not connected internally. VOUT Pin The VOUT pin is the regulated output of the post regulator. When the MAQ5280 is enabled, VOUT regulates at a fixed voltage, when disabled, VOUT is high impedance. A 2.2ìF or larger ceramic capacitor must be connected to VOUT pin-to-ground.