LM5010AEVAL/NOPB National Semiconductor, LM5010AEVAL/NOPB Datasheet - Page 8

• Manufacturer Part Number: LM5010AEVAL/NOPB
• Description: EVAL BOARD FOR LM5010A
• Manufacturer: National Semiconductor

Specifications of LM5010AEVAL/NOPB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Functional Description
The LM5010A Step Down Switching Regulator features all
the functions needed to implement a low cost, efficient buck
DC-DC converter capable of supplying in excess of 1A to the
load. This high voltage regulator integrates an 80V N-Channel
buck switch, with an easy to implement constant on-time con-
troller. It is available in the thermally enhanced LLP-10 and
TSSOP-14EP packages. The regulator compares the feed-
back voltage to a 2.5V reference to control the buck switch,
and provides a switch on-time which varies inversely with VIN.
This feature results in the operating frequency remaining rel-
atively constant with load and input voltage variations. The
switching frequency can range from less than 100 kHz to 1.0
MHz. The regulator requires no loop compensation resulting
in very fast load transient response. The valley current limit
circuit holds the buck switch off until the free-wheeling induc-
tor current falls below the current limit threshold, nominally set
at 1.25A.
The LM5010A can be applied in numerous applications to ef-
ficiently step down higher DC voltages. This regulator is well
FIGURE 1. Startup Sequence
8
suited for 48V telecom applications, as well as the 42V auto-
motive power bus. Features include: Thermal shutdown, VCC
under-voltage lock-out, gate drive under-voltage lock-out, and
maximum duty cycle limit.
Control Circuit Overview
The LM5010A employs a control scheme based on a com-
parator and a one-shot on-timer, with the output voltage feed-
back (FB) compared to an internal 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 program-
ming resistor (R
off for a fixed 260 ns off-time, or until the FB voltage falls below
the reference, whichever is longer. The buck switch then turns
on for another on-time period. Referring to the Block Diagram,
the output voltage is set by R1 and R2. The regulated output
voltage is calculated as follows:
The LM5010A requires a minimum of 25 mV of ripple voltage
at the FB pin for stable fixed-frequency operation. If the output
V
OUT
ON
). Following the on-time the switch remains
= 2.5V x (R1 + R2) / R2
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