TD7580 [ETC]

4A 240KHZ 23V PWM Buck DC/DC Converter; 4A 240KHZ 23V PWM降压型DC / DC转换器


型号：	TD7580
厂家：	ETC
描述：	4A 240KHZ 23V PWM Buck DC/DC Converter 4A 240KHZ 23V PWM降压型DC / DC转换器转换器
文件：	总13页 (文件大小：333K)
中文：	中文翻译
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Datasheet

4A 240KHZ 23V PWM Buck DC/DC Converter

TD7580

汪工 TEL:13828719410 QQ:1929794238

General Description

Features

The TD7580 is a 240 KHz fixed frequency

monolithic step down switch mode regulator

with a built in internal Power MOSFET. It

achieves 4A continuous output current over a

wide input supply range with excellent load

and line regulation.

4A Constant Output Current

80mΩ R_DSONInternal Power PMOSFET

Switch

Up to 95% Efficiency

Fixed 240KHz Frequency

Wide 3.6V to 23V Input Voltage Range

Output Adjustable from 1.222V to 21V

Built in Frequency Compensation

Built in Thermal Shutdown Function

Built in Current Limit Function

SOP-8 Package is Available

The minimum dropout up to 0.3V

The device includes a voltage reference,

oscillation circuit, error amplifier, internal

PMOS and etc.

The PWM control circuit is able to adjust the

duty ratio linearly from 0 to 100%. An enable

function, an over current protection function

and a short circuit protection function are

built inside. An internal compensation block

is built in to minimize external component

count.

Applications

Portable DVD

LCD Monitor / TV

Battery Charger

ADSL Modem

The TD7580 serves as ideal power supply

units for portable devices.

Telecom / Networking Equipment

Figure 1 Package Type of TD7580

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Pin Configurations

Figure 2 Pin Configuration of TD7580 (Top View)

Pin Description

Pin Number Pin Name Description

1,6, 8

Not Connect.

Supply Voltage Input Pin. TD7580 operates from a 3.6V to 23V

DC voltage. Bypass Vin to GND with a suitably large capacitor

to eliminate noise on the input.

Vin

Power Switch Output Pin. SW is the switch node that supplies

power to the output.

Ground Pin. Care must be taken in layout. This pin should be

placed outside of the Schottky Diode to output capacitor ground

path to prevent switching current spikes from inducing voltage

noise into TD7580.

GND

Feedback Pin. Through an external resistor divider network, FB

senses the output voltage and regulates it. The feedback

threshold voltage is 1.222V.

Enable Pin. EN is a digital input that turns the regulator on or

off .Drive EN pin high to turn on the regulator, drive it low to

turn it off.

Ordering Information

TD7580

Packing

Blank: Tube

Circuit Type

Type and Reel

Package

P: SOP8

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Function Block

Figure 3 Function Block Diagram of TD7580

Absolute Maximum Ratings

Parameter

Symbol

V_IN

Value

-0.3 to 23

-0.3 to Vin

-0.3 to 12

-0.3 to Vin

Unit

Input Voltage

Feedback Pin Voltage

V_FB

Enable Pin Voltage

V_EN

Switch Pin Voltage

V_SW

Pout

T_J

Output Power Limited

Operating Junction Temperature

Storage Temperature

150

ºC

-65 to 150

260

ºC

T_STG

T_LEAD

Lead Temperature (Soldering, 10 sec)

ESD (HBM)

ºC

2000

Thermal Resistance-Junction to Ambient

Thermal Resistance-Junction to Case

ºC / W

RθJA

RθJC

Note1: Stresses greater than those listed under Maximum Ratings may cause permanent damage

to the device. This is a stress rating only and functional operation of the device at these or any

other conditions above those indicated in the operation is not implied. Exposure to absolute

maximum rating conditions for extended periods may affect reliability.

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Recommended Operating Conditions

Parameter

Symbol

V_IN

Min.

3.6

Max.

Unit

Input Voltage

Operating Junction Temperature

Operating Ambient Temperature

T_J

-40

125

ºC

T_A

-40

ºC

Electrical Characteristics

V_CC= 12V, T_a= 25℃ unless otherwise specified.

Parameters

Input voltage

Symbol

V_IN

Test Condition

Min. Typ. Max. Unit

3.6

Shutdown Supply Current

Supply Current

I_STBY

V_EN=0V

I_CC

V_FB

I_FB

V_EN=2V, V_FB=1.3V

V_IN= 3.6V to 23V

V_FB=1.3V

3.6

Feedback Voltage

1.185 1.222 1.26

Feedback Bias Current

Switch Current Limit

0.1

0.5

5.6

I_LIM

Oscillator Frequency

F_OSC

F_OSC1

V_EN

200

0.7

240

280 KHz

KHz

Frequency of Current

Limit or Short Circuit

Protection

V_FB=0V

EN Pin Threshold

1.2

1.7

I_H

I_L

V_EN=2.5V

V_EN=0.5V

-0.1

-3

-1

EN Pin Input Leakage

Current

-10

V_IN=12V, V_FB=0V

V_EN=12V, Iout=4A

Internal PMOS R_DSON

Max. Duty Cycle

R_DSON

D_MAX

mΩ

V_FB=0V, I_SW=0.1A

100

V_IN=12V ,Vout=5V

Iout=4A

Efficiency

Thermal Shutdown

T_OTSD

165

ºC

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Typical Performance Characteristics

Figure 5. Vfb vs. Temperature

Figure 4. Switching Frequency vs. Temperature

Figure 6. Icc vs. Temperature

Figure 7. Efficiency vs. Load (Vin=10V)

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Typical Application Circuit

R2=2K

R1=6.2K

15uh/4A

5V4A

TD7580

SB540

330uF

35V

5.5V~23V

DC INPUT

Fig8. TD7580 Typical Application Circuit @ 5V/4A

Note:In PCB layout. Reserved an area for CFF

R2=3.6K

R1=6.2K

3.3V4A

15uh/4A

TD7580

330uF

SB540

35V

4.5V~23V

DC INPUT

Fig9. TD7580 Typical Application Circuit @ 3.3V/4A

Note:In PCB layout. Reserved an area for CFF

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

R1=6.2K

R2=2K

15uh/4A

5V4A

TD7580

SB540

330uF

35V

5.5V~23V

DC INPUT

Fig10. TD7580 Typical Application Circuit (with ceramic output capacitor) @ 5V/4A

Note:In PCB layout. Reserved an area for CFF

R2=3.6K

R1=6.2K

15uh/4A

3.3V4A

TD7580

SB540

330uF

35V

4.5V~23V

DC INPUT

Fig11. TD7580 Typical Application Circuit (with ceramic output capacitor) @ 3.3V/4A

Note:In PCB layout. Reserved an area for CFF

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Schottky Rectifier Selection Guide

Vin (Max)

4A Load Current

Part Number

SB540

Vendor

23V

SR540

NA05QSA035

Table 1 lists some rectifier manufacturers.

No.

Vendor

Web Site

Nihon Inter

www.niec.co.jp

Fairchild Semiconductor

General Semiconductor

International Rectifier

On Semiconductor

Pan Jit International

www.fairchildsemi.com

www.gensemi.com

www.irf.com

www.onsemi.com

www.panjit.com.tw

Table 2 Schottky Diode manufacturers.

Output Voltage VS R1, R2 Resistor Selection Guide

Vout = (1+R1/R2)*1.222V

8.2K

Vout

1.8V

2.5V

3.3V

3.9K

3.2K

6.2K

13K

16K

3.6K

12V

1.8K

Table 3. Vout VS. R1, R2 Select Table

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

temperatures require more heat sinking.

Function Description

For the best thermal performance, wide copper

traces and generous amounts of printed circuit

board copper should be used in the board layout.

(Once exception to this is the output (switch) pin,

which should not have large areas of copper.)

Large areas of copper provide the best transfer of

heat (lower thermal resistance) to the surrounding

air, and moving air lowers the thermal resistance

even further.

Pin Functions

V_IN

This is the positive input supply for the IC

switching regulator. A suitable input bypass

capacitor must be present at this pin to minimize

voltage transients and to supply the switching

currents needed by the regulator

Gnd

Package thermal resistance and junction

temperature rise numbers are all approximate,

and there are many factors that will affect these

numbers. Some of these factors include board

size, shape, thickness, position, location, and

even board temperature. Other factors are, trace

width, total printed circuit copper area, copper

thickness, single or double-sided, multi-layer

board and the amount of solder on the board.

Circuit ground.

Internal switch. The voltage at this pin switches

between (V_IN– V_SAT) and approximately – 0.5V,

with a duty cycle of approximately V_OUT/ V_IN. To

minimize coupling to sensitive circuitry, the PC

board copper area connected to this pin should

be kept a minimum.

The effectiveness of the PC board to dissipate

heat also depends on the size, quantity and

spacing of other components on the board, as

well as whether the surrounding air is still or

moving. Furthermore, some of these components

such as the catch diode will add heat to the PC

board and the heat can vary as the input voltage

changes. For the inductor, depending on the

physical size, type of core material and the DC

resistance, it could either act as a heat sink taking

heat away from the board, or it could add heat to

the board.

Senses the regulated output voltage to complete

the feedback loop.

Allows the switching regulator circuit to be

shutdown using logic level signals thus dropping

the total input supply current to approximately

30uA. Pulling this pin below a threshold voltage of

approximately 0.7 V turns the regulator down, and

pulling this pin above 1.3V (up to a maximum of

12V) shuts the regulator on. For automatic starup

condition , can be implemented by the addition of

a resistive voltage divider from V^INto GND.

Thermal Considerations

Setting the Output Voltage

The output voltage is set using a resistive

voltage divider from the output voltage to FB. The

voltage divider divides the

The TD7580 is available in SOP8 package.

output voltage down by the ratio:

VFB = VOUT * R2 / (R1 + R2)

Thus the output voltage is:

VOUT = 1.222 * (R1 + R2) / R2

R2 can be as high as 100KΩ, but a typical

value is 10KΩ. Using that value, R1 is

determined by:

R1 ~= 8.18 * (VOUT – 1.222) (KΩ)

For example, for a 3.3V output voltage, R2 is

10KΩ, and R1 is 17KΩ.

The SOP8 package needs a heat sink under most

conditions. The size of the heat sink depends on

the input voltage, the output voltage, the load

current and the ambient temperature. The

TD7580 junction temperature rises above

ambient temperature for a 4A load and different

input and output voltages. The data for these

curves was taken with the TD7580 (SOP8

package) operating as a buck-switching regulator

in an ambient temperature of 25^oC (still air).

These temperature rise numbers are all

approximate and there are many factors that can

affect these temperatures. Higher ambient

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

The output capacitor is required to maintain

the DC output voltage. Low ESR capacitors

are preferred to keep the output voltage ripple

low. The characteristics of the output

capacitor also affect the stability of the

regulation control system. Ceramic, tantalum,

or low ESR electrolytic capacitors are

recommended. In the case of ceramic

capacitors, the impedance at the switching

frequency is dominated by the capacitance,

and so the output voltage ripple is mostly

independent of the ESR. The output voltage

ripple is estimated to be:

VRIPPLE ~= 1.4 * VIN * (fLC/fSW)^2

Where VRIPPLE is the output ripple voltage, VIN

is the input voltage, fLC is the resonant

frequency of the LC filter, fSW is the switching

frequency. In the case of tanatalum or low-

ESR electrolytic capacitors, the ESR

dominates the impedance at the switching

frequency, and so the output ripple is

calculated as:

Inductor

The inductor is required to supply constant

current to the output load while being driven by

the switched input voltage. A larger value

inductor results in less ripple current that in

turn results in lower output ripple voltage.

However, the larger value inductor has a larger

physical size, higher series resistance, and/or

lower saturation current. Choose an inductor

that does not saturate under the worst-case

load conditions. A good rule for determining

the inductance is to allow the peak-to-peak

ripple current in the inductor to be approximately

30% of the maximum load

current. Also, make sure that the peak

inductor current (the load current plus half the

peak-to-peak inductor ripple current) is below

the TBDA minimum current limit. The

inductance value can be calculated by the

equation:

L = (VOUT) * (VIN-VOUT) / VIN * f * ΔI

Where VOUT is the output voltage, VIN is the

input voltage, f is the switching frequency, and

ΔI is the peak-to-peak inductor ripple current.

VRIPPLE ~= ΔI * RESR

Where VRIPPLE is the output voltage ripple, ΔI is

the inductor ripple current, and RESR is the

equivalent series resistance of the output

capacitors.

Input Capacitor

The input current to the step-down converter is

discontinuous, and so a capacitor is required

to supply the AC current to the step-down

converter while maintaining the DC input

voltage. A low ESR capacitor is required to

keep the noise at the IC to a minimum.

Ceramic capacitors are preferred, but tantalum

or low-ESR electrolytic capacitors may also

suffice.

Output Rectifier Diode

The output rectifier diode supplies the current

to the inductor when the high-side switch is off.

To reduce losses due to the diode forward

voltage and recovery times, use a Schottky

rectifier.

Table 1 provides the Schottky rectifier part

numbers based on the maximum input voltage

and current rating.

The input capacitor value should be greater

than 10μF. The capacitor can be electrolytic,

tantalum or ceramic. However since it absorbs

the input switching current it requires an

adequate ripple current rating. Its RMS current

rating should be greater than approximately

1/2 of the DC load current.

For insuring stable operation should be

placed as close to the IC as possible.

Alternately a smaller high quality ceramic

0.1μF capacitor may be placed closer to the IC

and a larger capacitor placed further away. If

using this technique, it is recommended that

the larger capacitor be a tantalum or

electrolytic type. All ceramic capacitors should

be places close to the TD7580.

Choose a rectifier who’s maximum reverse

voltage rating is greater than the maximum

input voltage, and who’s current rating is

greater than the maximum load current.

Feedforward Capacitor (CFF)

For output voltages greater than approximately

8V, an additional capacitor is required. The

compensation capacitor is typically between 100

pF and 33 nF, and is wired in parallel

with the output voltage setting resistor, R1. It

provides additional stability for high output

voltages, low input-output voltages, and/or very

low ESR output capacitors, such as solid

tantalum capacitors.

Output Capacitor

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

This capacitor type can be ceramic, plastic, silver

mica, etc.(Because of the unstable characteristics

of ceramic capacitors made with Z5U material,

they are not recommended.)

Note:In PCB layout. Reserved an area for CFF.

Over Current Protection (OCP)

The cycle by cycle current limit threshold is set

between 5A and 5.6A. When the load current

reaches the current limit threshold, the cycle by

cycle current limit circuit turns off the high side

switch immediately to terminate the current duty

cycle. The inductor current stops rising. The cycle

by cycle current limit protection directly limits

inductor peak current. The average inductor

current is also limited due to the limitation on peak

inductor current. When the cycle by cycle current

limit circuit is triggered, the output voltage drops

as the duty cycle is decreasing.

by input power minus output power.

P_{total _loss}= V _IN× I_IN– V _O× I_O

The power dissipation of inductor can be

approximately calculated by output current and

DCR of inductor.

P_inductor_loss= I_O²× R_inductor× 1.1

The junction to ambient temperature can be got

from power dissipation in the TD7580 and thermal

impedance from junction to ambient.

T _(jun-amb)=(P_totalloss–P_inductorloss)× Θ_JA

The maximum junction temperature of TD7580 is

145°C, which limits the maximum load current

capability. Please see the thermal de-rating

curves for the maximum load current of the

TD7580 under different ambient temperatures.

The thermal performance of the TD7580 is trongly

affected by the PCB layout. Extra care should be

taken by users during the design process to nsure

that the IC will operate under the recommended

environmental conditions.

Several layout tips are listed below for the best

electric and thermal performance.

1. Do not use thermal relief connection to the VIN

and the GND pin. Pour a maximized copper area

to the GND pin and the VIN pin to help thermal

dissipation.

2. Input capacitor should be connected to the VIN

pin and the GND pin as close as possible.

3. Make the current trace from VOUT pins to L to

the GND as short as possible.

4. Pour copper plane on all unused board area

and connect it to stable DC nodes, like VIN, GND,

or VOUT.

Thermal Management and Layout

Consideration

In the TD7580 buck regulator circuit, high pulsing

current flows through two circuit loops. The first

loop starts from the input capacitors, to the VIN

pin, to the VOUT pins, to the filter inductor, to the

output capacitor and load, and then returns to the

input capacitor through ground.

Current flows in the first loop when the high side

switch is on. The second loop starts from the

inductor, to the output capacitors and load, to the

GND pin of the TD7580, and to the VOUT pins of

the TD7580. Current flows in the second loop

when the low side diode is on.

In PCB layout, minimizing the two loops area

reduces the noise of this circuit and improves

efficiency. A ground plane is recommended to

connect input capacitor, output capacitor, and

GND pin of the TD7580.

5. Keep sensitive signal traces such as trace

connecting FB pin away from the VOUT pins.

In the TD7580 buck regulator circuit, the two

major power dissipating components are the

TD7580 and output inductor. The total power

dissipation of converter circuit can be measured

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Package Information

SOP8 Package Outline Dimensions

September, 2006

Techcode Semiconductor Limited

Datasheet

TD7580

4A 240KHZ 23V PWM Buck DC/DC Converter

Design Notes

September, 2006

Techcode Semiconductor Limited

TD7580 [ETC]

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