Datasheet

Vcc

Vin

Internal Enable Signal

3.5V

VIN and VCC

10V

3.7V

LM5118, LM5118-Q1

SNVS566G –APRIL 2008–REVISED FEBRUARY 2013

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FUNCTIONAL DESCRIPTION

High Voltage Start-Up Regulator

The LM5118 contains a dual mode, high voltage linear regulator that provides the VCC bias supply for the PWM

controller and the MOSFET gate driver. The VIN input pin can be connected directly to input voltages as high as

75V. For input voltages below 10V, an internal low dropout switch connects VCC directly to VIN. In this supply

range, VCC is approximately equal to VIN. For VIN voltages greater than 10V, the low dropout switch is disabled

and the VCC regulator is enabled to maintain VCC at approximately 7V. A wide operating range of 4V to 75V

(with a startup requirement of at least 5 volts) is achieved through the use of this dual mode regulator.

The output of the VCC regulator is current limited to 35 mA, typical. Upon power up, the regulator sources

current into the capacitor connected to the VCC pin. When the voltage at the VCC pin exceeds the VCC under-

voltage threshold of 3.7V and the UVLO input pin voltage is greater than 1.23V, the gate driver outputs are

enabled and a soft-start sequence begins. The gate driver outputs remain enabled until VCC falls below 3.5V or

the voltage at the UVLO pin falls below 1.13V.

In many applications the regulated output voltage or an auxiliary supply voltage can be applied to the VCCX pin

to reduce the IC power dissipation. For output voltages between 4V and 15V, VOUT can be connected directly to

VCCX. When the voltage at the VCCX pin is greater than 3.85V, the internal VCC regulator is disabled and an

internal switch connects VCCX to VCC, reducing the internal power dissipation.

In high voltage applications extra care should be taken to ensure the VIN pin voltage does not exceed the

absolute maximum voltage rating of 76V. During line or load transients, voltage ringing on the VIN line that

exceeds the absolute maximum rating can damage the IC. Both careful PC board layout and the use of quality

bypass capacitors located close to the VIN and GND pins are essential.

Figure 14. VIN and VCC Sequencing

Enable

The LM5118 contains an enable function which provides a very low input current shutdown mode. If the EN pin is

pulled below 0.5V, the regulator enters shutdown mode, drawing less than 10 µA from the VIN pin. Raising the

EN input above 3V returns the regulator to normal operation. The EN pin can be tied directly to the VIN pin if this

function is not needed. It must not be left floating. A 1MΩ pull-up resistor to VIN can be used to interface with an

open collector or open drain control signal.

UVLO

An under-voltage lockout pin is provided to disable the regulator when the input is below the desired operating

range. If the UVLO pin is below 1.13V, the regulator enters a standby mode with the outputs disabled, but with

VCC regulator operating. If the UVLO input exceeds 1.23V, the regulator will resume normal operation. A voltage

divider from the input to ground can be used to set a VIN threshold to disable the regulator in brown-out

conditions or for low input faults.

Product Folder Links: LM5118 LM5118-Q1