Datasheet

LM5119/LM5119Q

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SNVS676F –AUGUST 2010–REVISED FEBRUARY 2013

DETAILED OPERATING DESCRIPTION

The LM5119 high voltage switching regulator features all of the functions necessary to implement an efficient

dual channel buck regulator that operates over a very wide input voltage range. The LM5119 may be configured

as two independent regulators or as a single high current regulator with two interleaved channels. This easy to

use regulator integrates high-side and low-side MOSFET drivers capable of supplying peak currents of 2.5 Amps

(VCC = 8V). The regulator control method is based on current mode control utilizing an emulated current ramp.

Emulated peak current mode control provides inherent line feed-forward, cycle-by-cycle current limiting and ease

of loop compensation. The use of an emulated control ramp reduces noise sensitivity of the pulse-width

modulation circuit, allowing reliable processing of the very small duty cycles necessary in high input voltage

applications. The switching frequency is user programmable from 50kHz to 750kHz. An oscillator/synchronization

pin allows the operating frequency to be set by a single resistor or synchronized to an external clock. An under-

voltage lockout and channel2 enable pin allows either both regulators to be disabled or channel2 to be disabled

with full operation of channel1. Fault protection features include current limiting, thermal shutdown and remote

shutdown capability. The under-voltage lockout input enables both channels when the input voltage reaches a

user selected threshold and provides a very low quiescent shutdown current when pulled low. The LLP32

package features an exposed pad to aid in thermal dissipation.

FUNCTIONAL DESCRIPTION

High Voltage Start-Up Regulator

The LM5119 contains two internal high voltage bias regulators, VCC1 and VCC2, that provide the bias supply for

the PWM controllers and gate drive for the MOSFETs of each regulator channel. The input pin (VIN) can be

connected directly to an input voltage source as high as 65 volts. The outputs of the VCC regulators are set to

7.6V. When the input voltage is below the VCC set-point level, the VCC output will track the VIN with a small

dropout voltage. If VCC1 is in an under voltage condition, channel2 will be disabled. This interdependence is

necessary to prevent channel2 from running open loop in the single output interleaved mode when the channel2

error amplifier is disabled (if either VCC is in UV, both channels are disabled).

The outputs of the VCC regulators are current limited at 25mA (minimum) output capability. Upon power-up, the

regulators source current into the capacitors connected to the VCC pins. When the voltage at the VCC pins

exceed 4.9V and the UVLO pin is greater than 1.25V, both channels are enabled and a soft-start sequence

begins. Both channels remain enabled until either VCC pin falls below 4.7V, the UVLO pin falls below 1.25V or

the die temperature exceeds the thermal limit threshold.

When operating at higher input voltages the bias power dissipation within the controller can be excessive. An

output voltage derived bias supply can be applied to a VCC pins to reduce the IC power dissipation. The

VCCDIS input can be used to disable the internal VCC regulators when external biasing is supplied. If VCCDIS

>1.25V, the internal VCC regulators are disabled. The externally supplied bias should be coupled to the VCC

pins through a diode, preferably a Schottky (low forward voltage). VCCDIS has a 500kΩ internal pull-down

resistance to ground for normal operation with no external bias. The internal pull-down resistance can be

overridden by pulling VCCDIS above 1.25V through a resistor divider connected to an external bias supply.

The VCC regulator series pass transistor includes a diode between VCC and VIN that should not be forward

biased in normal operation.

If the external bias winding can supply VCC greater than VIN, an external blocking diode is required from the

input power supply to the VIN pin to prevent the external bias supply from passing current to the input supply

through the VCC pins. For VOUT between 6V and 14.5V, VOUT can be connected directly to VCC through a

diode. For VOUT < 6V, a bias winding on the output inductor can be added as shown in Figure 3.

Product Folder Links: LM5119/LM5119Q