LM5005MHX datasheet(10/21 Pages) NSC

部品番号	LM5005MHX

部品情報	High Voltage 2.5 Amp Buck Regulator

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Detailed Operating Description

The LM5005 high voltage switching regulator features all of

the functions necessary to implement an efficient high volt-

age buck regulator using a minimum of external compo-

nents. This easy to use regulator integrates a 75V

N-Channel buck switch with an output current capability of

2.5 Amps. The regulator control method is based on current

mode control utilizing an emulated current ramp. Peak cur-

rent 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 process-

ing of very small duty cycles necessary in high input voltage

applications. The operating frequency is user programmable

from 50kHz to 500kHz. An oscillator synchronization pin

allows multiple LM5005 regulators to self synchronize or be

synchronized to an external clock. The output voltage can be

set from 1.225V. Fault protection features include, current

limiting, thermal shutdown and remote shutdown capability.

The device is available in the TSSOP-20 package featuring

an exposed pad to aid thermal dissipation.

The functional block diagram and typical application of the

LM5005 is shown in Figure 1. The LM5005 can be applied in

numerous applications to efficiently step-down a high un-

regulated input voltage. The device is well suited for tele-

com, industrial and automotive power bus voltage ranges.

High Voltage Start-Up Regulator

The LM5005 contains a dual mode internal high voltage

startup regulator that provides the Vcc bias supply for the

PWM controller and boot-strap MOSFET gate driver. The

input pin (Vin) can be connected directly to the input voltage,

as high as 75 Volts. For input voltages below 9V, a low

dropout switch connects Vcc directly to Vin. In this supply

range, Vcc is approximately equal to Vin. For Vin voltage

greater than 9V, the low dropout switch is disabled and the

Vcc regulator is enabled to maintain Vcc at approximately

7V. The wide operating range of 7 to 75V is achieved through

the use of this dual mode regulator.

The output of the Vcc regulator is current limited to 20mA.

Upon power up, the regulator sources current into the ca-

pacitor connected to the Vcc pin. When the voltage at the

Vcc pin exceeds the Vcc UVLO threshold of 6.3V and the SD

pin is greater than 1.225V, the output switch is enabled and

a soft-start sequence begins. The output switch remains

enabled until Vcc falls below 5.3V or the SD pin falls below

1.125V.

An auxiliary supply voltage can be applied to the Vcc pin to

reduce the IC power dissipation. If the auxiliary voltage is

greater than 7.3V, the internal regulator will essentially shut-

off, reducing the IC power dissipation. The Vcc regulator

series pass transistor includes a diode between Vcc and Vin

that should not be forward biased in normal operation.

Therefore the auxiliary Vcc voltage should never exceed the

Vin voltage.

In high voltage applications extra care should be taken to

ensure the Vin pin 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

Ratings 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.

20161904

FIGURE 2. Vin and Vcc Sequencing

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