Functional Description

The LM5010 Step Down Switching Regulator features all the

functions needed to implement a low cost, efficient buck bias

power converter capable of supplying in excess of 1A to the

load. This high voltage regulator contains an N-Channel

buck switch, is easy to implement, and is available in the

thermally enhanced LLP-10 and TSSOP-14EP packages.

The regulator’s operation is based on a hysteretic control

scheme, and uses an on-time which varies inversely with

V

ing relatively constant with load and input voltage variations.

MHz. The hysteretic control requires no loop compensation

resulting in very fast load transient response. The valley

current limit detection circuit, internally set at 1.25A, holds

the buck switch off until the high current level subsides.

Figure 1 shows the functional block diagram. The LM5010

can be applied in numerous applications to efficiently regu-

late down higher voltages. This regulator is well suited for

48V telecom applications, as well as the new 42V automo-

tive power bus. Implemented as a Point-of-Load regulator

following a highly efficient intermediate bus converter can

result in high overall system efficiency. Features include:

Thermal shutdown, V

under-voltage lockout, and maximum duty cycle limit.

Hysteretic Control Circuit

Overview

The LM5010 buck DC-DC regulator employs a control

scheme based on a comparator and a one-shot on-timer,

with the output voltage feedback (FB) compared to an inter-

nal reference (2.5V). If the FB voltage is below the reference

the buck switch is turned on for a time period determined by

the input voltage and a programming resistor (R

ing the on-time the switch remains off for 265 ns, or until the

FB voltage falls below the reference, whichever is longer.

The buck switch then turns on for another on-time period.

20119911

FIGURE 8. Startup Sequence

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