LM25010EVAL National Semiconductor, LM25010EVAL Datasheet - Page 8

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LM25010EVAL

Manufacturer Part Number
LM25010EVAL
Description
BOARD EVALUATION LM25010
Manufacturer
National Semiconductor
Datasheets

Specifications of LM25010EVAL

Main Purpose
DC/DC, Step Down
Outputs And Type
1, Non-Isolated
Voltage - Output
5V
Current - Output
1A
Voltage - Input
6 ~ 42V
Regulator Topology
Buck
Frequency - Switching
200kHz
Board Type
Fully Populated
Utilized Ic / Part
LM25010
Lead Free Status / RoHS Status
Not applicable / Not applicable
Power - Output
-
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Functional Description
The LM25010 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 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 LM25010 can be applied in numerous applications to ef-
ficiently step-down higher DC voltages. Features include:
FIGURE 1. Startup Sequence
8
Thermal shutdown, VCC under-voltage lock-out, gate drive
under-voltage lock-out, and maximum duty cycle limit.
Control Circuit Overview
The LM25010 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 LM25010 requires a minimum of 25 mV of ripple voltage
at the FB pin for stable fixed-frequency operation. If the output
capacitor’s ESR is insufficient additional series resistance
may be required (R3 in the Block Diagram).
V
OUT
ON
). Following the on-time the switch remains
= 2.5V x (R1 + R2) / R2
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