1926.PDF

(94 KB) Pobierz

19-4781; Rev 0; 11/98

MAX1710 Evaluation Kit

General Description

The MAX1710 evaluation kit (EV kit) demonstrates the

data sheet’s standard 7A notebook CPU application cir-

cuit (see MAX1710/MAX1711 data sheet). This DC-DC

converter steps down high-voltage batteries and/or AC

adapters, generating a precision, low-voltage CPU core

rail.

The circuit was designed for a 7V to 24V battery range,

but accommodates from 4.5V to 24V. Some parameters,

such as load-transient response and maximum thermal

load capability, may be degraded by going outside the

7V to 24V range. The continuous output current rating,

based on worst-case MOSFET R

DS(ON)

, heat sinking,

and other thermal stress issues, is 5.5A at T

= +70°C.

This EV kit is a fully assembled and tested circuit

board. It also allows the evaluation of the MAX1711.

Features

High Speed, Accuracy, and Efficiency

Fast-Response QUICK-PWM™ Architecture

7V to 24V Input Voltage Range

1.25V to 2V Output Voltage Range

7A Peak Load-Current Capability

(5.5A Continuous)

93% Efficient (V

OUT

= 2V, V

BATT

= 7V,

LOAD

= 4A)

300kHz Switching Frequency

No Current-Sense Resistor

Remote GND and V

OUT

Sensing

Power-Good Output

24-Pin QSOP Package

Low-Profile Components

Fully Assembled and Tested

Evaluates: MAX1710/MAX1711

Ordering Information

PART

MAX1710EVKIT

TEMP. RANGE

0°C to +70°C

IC PACKAGE

24 QSOP

NOTE:

To evaluate the MAX1711, request a MAX1711EEG

free sample with the MAX1710 EV Kit.

Component List

DESIGNATION QTY

C1–C4

DESCRIPTION

4.7µF/25V ceramic capacitors

Taiyo Yuden TMK325BJ475K

C1–C4

(ALTERNATE)

10µF, 25V ceramic capacitors

Tokin C34Y5U1E106Z or

United Chemi Con/Marcon

THCR50E1E106ZT

470µF, 6.3V, 30mΩ low-ESR tantalum

capacitors

Kemet T510X477M006AS

10µF, 6.3V ceramic capacitor

Taiyo Yuden JMK325BJ106MN or

TDK C3225X5R1A106M

0.1µF ceramic capacitor

0.22µF ceramic capacitors

470pF ceramic capacitor

1µF ceramic capacitor

Not installed

2A Schottky diode

SGS-Thomson STPS2L25U or

Nihon EC31QS03L

100mA Schottky diode

Central Semiconductor CMPSH-3

Hitachi HRB0103A

DESIGNATION QTY

DESCRIPTION

1A Schottky diode

Motorola MBRS130LT3,

Nihon EC10QS03, or

International Rectifier 10BQ040

Hitachi HRF22

200mV switching diode

Central Semiconductor CMPD2838

2µH power inductor

Panasonic ETQP6F2R0HFA,

Coiltronics UP4B-2R2, or

Coilcraft DO5022P-222HC

N-channel MOSFET

International Rectifier IRF7807,

Fairchild FDS6612A, or

Siliconix Si4416DY

N-channel MOSFET

International Rectifier IRF7805,or

Fairchild FDS6670A, or

NEC uPA1706, or

Hitachi HAT2040R

20Ω, 5% resistor

C5, C6, C7

C11, C12

C14

C15

C16, C17, C18

QUICK-PWM is a trademark of Maxim Integrated Products.

________________________________________________________________

Maxim Integrated Products

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800

For small orders, phone 1-800-835-8769.

MAX1710 Evaluation Kit

Evaluates: MAX1710/MAX1711

Component List (continued)

DESIGNATION QTY

R2, R3, R9

R10, R12

JU1, JU2

None

SW1

SW2

None

DESCRIPTION

1MΩ, 5% resistors

100kΩ, 5% resistor

Not installed

3Ω, 5% resistor

1kΩ, 5% resistor

MAX1710EEG (24-QSOP)

2-pin headers

Shunt (JU1)

DIP-8 dip switch

Digi-Key CT2084-ND

Momentary switch, normally open

Digi-Key P8006/7S

Scope-probe connector Berg

Electronics 33JR135-1

MAX1710 PC board

MAX1710/MAX1711 data sheet

Equipment Needed

• 7V to 24V, >20W power supply, battery, or notebook

AC adapter

• DC bias power supply, 5V at 100mA

• Dummy load capable of sinking 7A

• Digital multimeter (DMM)

• 100MHz dual-trace oscilloscope

Quick Start

1) Ensure that the circuit is connected correctly to the

supplies and dummy load prior to applying any

power.

2) Ensure that the shunt is connected at JU1 (SHDN

3) Turn on battery power prior to +5V bias power; other-

wise, the output UVLO timer will time out and the

fault latch will be set, disabling the regulator until

+5V power is cycled or shutdown is toggled.

4) Observe the output with the DMM and/or oscillo-

scope. Look at the LX switching-node and MOSFET

gate-drive signals while varying the load current.

5) Don’t change the DAC code without cycling +5V bias

power; otherwise, the output voltage ramp will prob-

ably bump into the over- or undervoltage protection

thresholds and latch the circuit off. If this happens,

just cycle power or

press the RESET button.

6) Set switch SW1 per Table 1 to get the desired output

voltage.

Component Suppliers

SUPPLIER

Central

Semiconductor

Coilcraft

Coiltronics

Dale-Vishay

Fairchild

Hitachi

International

Rectifier

IRC

Kemet

Motorola

NEC

Nihon

Panasonic

Sanyo

SGS-Thomson

Siliconix

Sumida

Taiyo Yuden

TDK

Tokin

PHONE

516-435-1110

708-639-6400

561-241-7876

402-564-3131

408-721-2181

888-777-0384

310-322-3331

512-992-7900

408-986-0424

602-303-5454

408-588-6000

847-843-7500

714-373-7939

619-661-6835

617-259-0300

408-988-8000

708-956-0666

408-573-4150

847-390-4373

408-432-8020

FAX

516-435-1824

708-639-1469

561-241-9339

402-563-6418

408-721-1635

650-244-7947

310-322-3332

512-992-3377

408-986-1442

602-994-6430

408-588-6130

847-843-2798

714-373-7183

619-661-1055

617-259-9442

408-970-3950

708-956-0702

408-573-4159

847-390-4428

408-434-0375

Detailed Description

This 7A buck-regulator design is optimized for a

300kHz frequency and output voltage settings around

1.6V. At lower output voltages, transient response is

degraded slightly and efficiency worsens. At higher

output voltages (approaching 2V), output ripple and

reflected input ripple increase.

The PC board layout deliberately includes long output

power and ground buses in order to facilitate evaluation

of the remote sense circuitry and to provide plenty of

experimentation space for soldering in different types of

output filter capacitors. These buses are also useful for

introducing the small amounts of parasitic trace resis-

tance necessary when using capacitors having high-

frequency ESR zeros (see the

All-Ceramic-Capacitor

Application

section in MAX1710/MAX1711 data sheet).

Position the experimental ceramic capacitors at differ-

ent places along the length of the buses to see the

effect of different amounts of ESR.

_______________________________________________________________________________________

MAX1710 Evaluation Kit

Table 1. MAX1710/1711 Output Voltage

Adjustment Settings

OUTPUT

VOLTAGE (V)

2.00

1.95

1.90

1.85

1.80

1.75

1.70

1.65

1.60

1.55

1.50

1.45

1.40

1.35

1.30

1.25

generator at a low duty cycle (10%) to minimize heat

stress in the MOSFET. Vary the high-level output voltage

of the pulse generator to vary the load current.

To determine the load current, you might expect to

insert a meter in the load path, but this method is pro-

hibited here by the need for low resistance and induc-

tance in the path of the dummy-load MOSFET. There

are two easy alternative methods to determine how

much load current a particular pulse-generator ampli-

tude is causing. The first and best is to observe the

inductor current with a calibrated AC current probe,

such as a Tektronix AM503. In the buck topology, the

load current is equal to the average value of the induc-

tor current. The second method is to first put on a static

dummy load and measure the battery current. Then,

connect the MOSFET dummy load at 100% duty

momentarily, and adjust the DC gate-drive signal

amplitude until the battery current rises to the appropri-

ate level (the MOSFET load must be well heatsinked for

this to work without causing smoke and flames).

Evaluates: MAX1710/MAX1711

Efficiency Measurements

Testing the power conversion efficiency P

OUT/

fairly

and accurately requires more careful instrumentation

than might be expected. One common error is to use

inaccurate DMMs. Another is to use only one DMM,

and move it from one spot to another to measure the

various input/output voltages and currents. This second

error usually results in changing the exact conditions

applied to the circuit due to series resistance in the

ammeters. It’s best to get four 3-1/2 digit or better

DMMs that have been recently calibrated, and monitor

BATT

, V

OUT

, I

BATT

, and I

LOAD

simultaneously, using

separate test leads directly connected to the input and

output PC board terminals. Note that it’s inaccurate to

test efficiency at the remote V

OUT

and ground termi-

nals, as this incorporates the parasitic resistance of the

PC board output and ground buses in the measure-

ment (a significant power loss).

Remember to include the power consumed by the +5V

bias supply when making efficiency calculations:

Efficiency

OUT

⋅

LOAD

BATT

⋅

BATT

)

(5V

⋅

BIAS

)

Setting the Output Voltage

Select the output voltage using the D0–D3 pins. The

MAX1710/MAX1711 uses an internal DAC as a feedback

resistor voltage-divider. The output voltage can be digi-

tally set from 1.25V to 2V, in 50mV increments, using

the D0–D3 inputs. Switch SW1 sets the desired output

voltage (Table 1).

Load-Transient Measurement

One interesting experiment is to subject the output to

large, fast load transients and observe the output with

an oscilloscope. This necessitates careful instrumenta-

tion of the output, using the supplied scope-probe jack.

Accurate measurement of output ripple and load-tran-

sient response invariably requires that ground clip

leads be completely avoided and that the probe hat be

removed to expose the GND shield, so the probe can

be plugged directly into the jack. Otherwise, EMI and

noise pickup will corrupt the waveforms.

Most benchtop electronic loads intended for power-sup-

ply testing lack the ability to subject the DC-DC convert-

er to ultra-fast load transients. Emulating the supply cur-

rent

∆i/∆t

at the CPU VCORE pins requires at least

10A/µs load transients. One easy method for generating

such an abusive load transient is to solder a MOSFET,

such as an MTD3055 or 12N05, directly across the

scope-probe jack then drive its gate with a strong pulse

The choice of MOSFET has a large impact on efficiency

performance. The International Rectifier MOSFETs used

were of leading-edge performance for the 7A applica-

tion at the time this kit was designed. However, the

pace of MOSFET improvement is rapid, so the latest

offerings should be evaluated.

_______________________________________________________________________________________

MAX1710 Evaluation Kit

Evaluates: MAX1710/MAX1711

Jumper and Switch Settings

Table 2. Jumper JU1 Functions

(Shutdown Mode)

SHUNT

LOCATION

Off

SHDN

Connected to

GND

MAX1710

OUTPUT

MAX1710 enabled

Shutdown mode,

OUT

= 0

Table 5. Jumper JU6 Functions

(Fixed/Adj. Current-Limit Selection)

SHUNT

LOCATION

ILIM PIN

Connected to V

CURRENT-LIMIT

THRESHOLD

100mV (default)

Off

Connected to GND via

external resistor R6. Refer to

Adjustable

the ILIM line in the

between 50mV

Description

(MAX1710/

and 200mV

MAX1711 data sheet) for

information on selecting R6.

Table 3. Jumper JU2 Functions

(Low-Noise Mode)

SHUNT

LOCATION

SKIP

Connected to

OPERATIONAL

MODE

Low-noise mode, forced fixed-

frequency PWM operation.

Normal operation, allows auto-

matic PWM/PFM switchover

for pulse skipping at light load,

resulting in highest efficiency.

Table 6. Jumpers JU7/JU10 Functions

(GNDS Integrator Disable Selection)

JUMPER

JU7

JU10

SHUNT

LOCATION

Off

GND PIN

Connected

to V

Connected

to GND

directly at

the load

GROUND

REMOTE-SENSE

Disables the

GNDS integrator

GNDS internally

connects to the

integrator that

fine-tunes the

ground offset

voltage.

Off

Connected to

GND

JU7

JU10

Off

Table 7. Jumpers JU8/JU9 Functions (FBS

and FB Integrator Disable Selection)

Table 4. Jumpers JU3/JU4/JU5 Functions

(Switching-Frequency Selection)

JUMPER

JU3

JU4 and JU5

JU4

JU3 and JU5

JU5

JU3 and JU4

JU3, JU4, JU5

SHUNT

LOCATION

Off

TON PIN

Connected

to V

Connected

to REF

Connected

to GND

Floating

FREQUENCY

(kHz)

200

400

550

300

JU8

JU9

Off

JUMPER

JU8

JU9

SHUNT

LOCATION

Off

FBS PIN

Connected

to V

Connected

to V

OUT

directly at

the load

GROUND

REMOTE-SENSE

Disables the FBS

and the main FB-

REF integrators

FBS internally

connects to the

integrator that

fine-tunes the DC

output voltage.

IMPORTANT:

Don’t change the operating frequency without

first re-calculating component values, because the frequency

has a significant effect on the peak current-limit level, MOSFET

heating, PFM/PWM switchover point, output noise, efficiency,

and other critical parameters.

Table 8. Jumper JU11 Functions

(Overvoltage Protection Disable)

SHUNT

LOCATION

Off

OVP

Connected to V

Connected to GND

OVERVOLTAGE

PROTECTION

OVP disabled

Normal operation,

OVP is enabled.

_______________________________________________________________________________________

MAX1710 Evaluation Kit

Table 9. Troubleshooting Guide

SYMPTOM

Circuit won’t start when power is applied.

POSSIBLE PROBLEM

Power-supply sequencing: +5V

bias supply was applied first.

Output overvoltage due to

shorted high-side MOSFET.

Output overvoltage due to load

recovery overshoot

Overload condition

Circuit won’t start when RESET

is pressed, +5V bias supply cycled.

Transient overload condition

SOLUTION

Press the RESET button.

Replace the MOSFET.

Reduce the inductor value, raise the switching

frequency, or add more output capacitance.

Remove the excessive load or raise the ILIM

threshold by changing R

LIM

(R6).

Add more low-ESR output capacitors.

Evaluates: MAX1710/MAX1711

Troubleshoot the power stage. Are the DH and DL

gate-drive signals present? Is the 2V V

REF

pre-

Broken connection, bad MOSFET, sent? Exercising

OVP

mode and then

SKIP

or other catastrophic problem.

no-fault mode can help you decipher the nature of

the problem (see MAX1710/MAX1711 data sheet

Pin Description).

VBATT power source has poor

impedance characteristic.

On-time pulses are erratic or have

unexpected changes in period.

Noise is being injected into FB.

FB is crossing the +12.5% OVP

threshold or the -70% UVLO

threshold due to fast DAC

response.

Add a bulk electrolytic bypass capacitor across

the benchtop power supply, or substitute a real

battery.

Add an RC filter on FB (1kΩ and 100pF

suggested) at R11 and C18.

This is a normal operating condition. If desired,

disable the OVP fault circuit via the

OVP

input

(JU11) or raise the OVP threshold to >2V by

substituting a MAX1711 for the MAX1710.

Circuit latches off when DAC code is

changed.

Add parasitic PC board trace resistance between

Load-transient waveform shows excess

Instability due to low-ESR ceramic the LX-FB connection and the ceramic capacitor.

ringing

LX switching waveform exhibits

placed across fast

double-pulsing (pulses separated only

feedback path (FB-GND).

Substitute a different capacitor type (OS-CON, tan-

by a 500ns min off-time).

talum, aluminum electrolytic work well).

Observe the gate-source voltage of N2 during the

low-to-high LX node transition (this requires careful

instrumentation). Is the gate voltage being pulled

above 1.5V, causing N2 to turn on? Use a smaller

low-side MOSFET or add a higher-value BST resis-

tor (R7).

Use a smaller high-side MOSFET or add more

heatsinking.

Excessive EMI, poor efficiency at high

input voltages.

Gate-drain capacitance of N2 is

causing shoot-through cross-

conduction.

Poor efficiency at high input voltages,

N1 gets hot.

N1 has excessive gate

capacitance.

_______________________________________________________________________________________

Plik z chomika:

Kot_Maciek

Inne pliki z tego folderu:

1763.PDF (53 KB)
1748.PDF (96 KB)
1508.PDF (444 KB)
1500.PDF (278 KB)
1501.PDF (328 KB)

1926.PDF

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: