LM26001EVAL National Semiconductor, LM26001EVAL Datasheet

LM26001EVAL

Manufacturer Part Number

LM26001EVAL

Description

BOARD EVALUATION LM26001

Manufacturer

National Semiconductor

Series

PowerWise®r

Datasheets

1.LM26001MXAXNOPB.pdf (18 pages)

2.LM26001EVAL.pdf (6 pages)

Specifications of LM26001EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

3.3V

Current - Output

1.5A

Voltage - Input

4.5 ~ 38V

Regulator Topology

Buck

Frequency - Switching

305kHz

Board Type

Fully Populated

Utilized Ic / Part

LM26001

Lead Free Status / RoHS Status

Not applicable / Not applicable

Power - Output

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LM26001 Evaluation Board

Introduction

The LM26001 evaluation board is designed to demonstrate

the capabilities of the LM26001 switching regulator.

The LM26001 board, schematic shown in Figure 1, is con-

figured to provide an output of 3.3V at up to 1.5A from an

input range of 3.5V to 38V (a minimum of 4.5V is required for

startup). The nominal operating frequency is 305 kHz and

can be synchronized from +30% to -20% of nominal using

the SYNC connection post. The evaluation board is de-

signed to operate at ambient temperatures up to 75˚C.

Typical evaluation board waveforms and performance

curves are shown in Figures 2 through 7. Figures 8 and 9

show the pcb trace layout. To aid in the design and evalua-

tion of dc/dc buck converters based on the LM26001 regu-

lator, the evaluation board can be re-configured for different

output voltages and operating frequencies. Test points are

also provided to enable easy connection and monitoring of

critical signals.

Table 2 shows the BOM for a second example circuit for 1.5V

output and 480 kHz switching frequency. This design oper-

ates from an input voltage of 3.5V to 38V and enters pulse

skipping mode at approximately 24Vin, depending on load-

ing.

For more information about device function and circuit de-

sign, refer to the LM26001 datasheet.

Jumper Settings

The FPWM jumper is used to disable the sleep mode func-

tion. For normal operation, select ‘off’, which connects

FPWM to GND. For FPWM operation (sleep mode disabled),

select ‘on’. The Vbias jumper connects the VBIAS pin to

Vout. When Vout is greater than 3V, the VBIAS function will

be activated for improved efficiency. To disable VBIAS, or if

Vout is set to less than 3V, set the jumper to ‘GND’.

Optional Components

Before changing the default components, please refer to the

product datasheet for information regarding component se-

lection.

AN201871

National Semiconductor

Application Note 1454

Allan Fisher

August 2006

Output voltage and frequency are easily adjustable with

single resistors, R1 and R3 respectively. However, large

changes to the default settings may require other changes to

the inductor, output capacitor, and compensation network.

Several optional component pads have been provided for

application flexibility.

The C7 pad is provided for an additional ceramic output

capacitor. This capacitor can be used to lower the total ESR

at the output. D2 blocks reverse current to the input supply

during low input voltage and light load conditions. This diode

may not be necessary in all applications and can be replaced

with a jumper.

C10 is a phase lead capacitor which can be installed to

increase phase and gain margin. See the compensation

section of the datasheet for more detailed information.

Powering Up

Before powering up the LM26001 evaluation board, all ex-

ternal connections should be verified. The power supply

input must be turned off and connected with proper polarity

to the VIN and GND posts. The load should be connected

between the VOUT post and GND post. Both the VIN and

VOUT connections should use the GND post closest to the

VIN post. Output voltage can be monitored with a DVM or

oscilloscope at the VOUT post.

The second GND post, close to the IC, is provided primarily

for small signal measurements, such as soft-start voltage, or

PGOOD. This GND post should also be used when applying

optional external signals such as EN and SYNC.

Once all connections have been verified, input power can be

applied. The input voltage must be set between 4.5V and

38V. The load can be on or off at startup. If the EN post is left

open, the output voltage will ramp up when VIN is applied

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LM26001EVAL Summary of contents

Page 1

... Vout is set to less than 3V, set the jumper to ‘GND’. Optional Components Before changing the default components, please refer to the product datasheet for information regarding component se- lection. © 2006 National Semiconductor Corporation National Semiconductor Application Note 1454 Allan Fisher August 2006 Output voltage and frequency are easily adjustable with single resistors, R1 and R3 respectively ...

Page 2

TABLE 1. LM26001 Bill of Materials for V Ref # C1 3.3µF 50V X7R ceramic C2 47µF 50V low ESR electrolytic C3 10µF 10V B ceramic C4 0.1µF 50V COG ceramic C5 10nF 50V X7R ceramic C6 100µF 8V 12mohm ...

Page 3

Performance Characteristics Unless otherwise specified, VIN = 12V, T FIGURE 2. Start-Up Waveforms (I = 1A) OUT FIGURE 3. PWM Waveforms (I = 1A) OUT FIGURE 4. Sleep Mode Waveforms (I = 25mA) OUT = 25˚C. A 20187102 FIGURE 5. ...

Page 4

PCB Layout Diagram(s) www.national.com FIGURE 8. Top Side Layout 4 20187108 ...

Page 5

PCB Layout Diagram(s) TABLE 2. LM26001 Bill of Materials for V Ref # C1 3.3µF 50V X7R ceramic C2 47µF 50V electrolytic C3 10µF 10V B ceramic C4 0.1µF 50V COG ceramic C5 10nF 50V X7R ceramic C6 100µF 8V ...

Page 6

... BANNED SUBSTANCE COMPLIANCE National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at: www.national.com/quality/green. ...

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