ACT4060SH - Active-Semi, Inc.

Innovative Products. Active Solutions. - 1 - www.active-semi.com

FEATURES

 2A Output Current

 Up to 95% Efficiency

 4.75V to 20V Input Range

 8µA Shutdown Supply Current

 420kHz Switching Frequency

 Adjustable Output Voltage

 Cycle-by-Cycle Current Limit Protection

 Thermal Shutdown Protection

 Frequency FoldBack at Short Circuit

 Stability with Wide Range of Capacitors,

Including Low ESR Ceramic Capacitors

 SOP-8 Package

APPLICATIONS

 TFT LCD Monitors

 Portable DVDs

 Car-Powered or Battery-Powered Equipments

 Set-Top Boxes

 Telecom Power Supplies

 DSL and Cable Modems and Routers

 Termination Supplies

GENERAL DESCRIPTION

The ACT4060 is a current-mode step-down DC/DC

converter that generates up to 2A of output current

at 420kHz switching frequency. The device utilizes

Active-Semi’s proprietary ISOBCD20 process for

operation with input voltages up to 20V.

Consuming only 8μA in shutdown mode, the

ACT4060 is highly efficient with peak operating effi-

ciency at 95%. Protection features include cycle-by-

cycle current limit, thermal shutdown, and frequency

foldback at short circuit.

The ACT4060 is available in a SOP-8 package and

requires very few external devices for operation.

TYPICAL APPLICATION CIRCUIT

ACT4060

Rev8, 24-Jul-07

Wide Input 2A Step Down Converter

ACT4060

Innovative Products. Active Solutions. - 2 - www.active-semi.com

Rev8, 24-Jul-07

ORDERING INFORMATION

PART NUMBER TEMPERAT URE RANGE PACKAGE PINS PACKING

ACT4060SH -40°C to 85°C SOP-8 8 TUBE

ACT4060SH-T -40°C to 85°C SOP-8 8 TAPE & REEL

PIN CONFIGURATION

PIN DESCRIPTIONS

PIN NUMBER PIN NAME PIN DESCRIPTION

1 BS Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver.

Connect a 10nF capacitor between BS and SW.

2 IN Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor

in the Application Information section.

3 SW Switch Out put. Connect this pin to the switching end of the inductor.

4 G Ground.

5 FB Feedback Input. The voltage at this pin is regulated to 1.293V. Connect to the

resistor divider between output and ground to set output voltage.

6 COMP Compensation Pin. See Stability Compensation in the Application Information

section.

7 EN Enabl e Input. W hen higher than 1.3V, this pin turns the IC on. When lower than

0.7V, this pin turns the IC off. Output voltage is discharged when the IC is off.

When left unconnected, EN is pulled up to 4.5V tip with a 2µA pull-up current.

8 N/C Not Connected.

SOP-8

ACT4060

Innovative Products. Active Solutions. - 3 - www.active-semi.com

Rev8, 24-Jul-07

ABSOLUTE MAXIMUM RATINGS

PARAMETER VALUE UNIT

IN Supply Voltage -0.3 to 25 V

SW Voltage -1 to VIN + 1 V

BS Voltage VSW - 0.3 to VSW + 8 V

EN, FB, COMP Voltage -0.3 to 6 V

Continuous SW Current Internally Limited A

Junction to Ambient Thermal Resistance (θJA) 105 °C/W

Maximum Power Dissipation 0.76 W

Operating Junction Temperature -40 to 150 °C

Storage Temperature -55 to 150 °C

Lead Temperature (Soldering, 10 sec) 300 °C

ELECTRICAL CHARACTERISTICS

(VIN = 12V, TA = 25°C, unless otherwise specified.)

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT

Input Voltage VIN VOUT = 5V, ILOAD = 0A to 1A 7 20 V

Feedback Voltage VFB 4.75V ≤ VIN ≤ 20V, VCOMP = 1.5V 1.267 1.293 1.319 V

High-Side Switch On Resistance RONH 0.20 Ω

Low-Side Switch On Resistance RONL 4.7 Ω

SW Leakage VEN = 0 0 10 µA

Current Limit ILIM 2.4 2.85 A

COMP to Current Limit

Transconductance GCOMP 1.8 A/V

Error Amplifier Transconductance GEA ΔICOMP = ±10µA 550 µA/V

Error Amplifier DC Gain AVEA 4000 V/V

Switching Frequency fSW 350 420 490 kHz

Short Circuit Switching Frequency VFB = 0 50 kHz

Maximum Duty Cycle DMAX VFB = 1.1V 90 %

Minimum Duty Cycle VFB = 1.4V 0 %

Enable Threshold Voltage Hysteresis = 0.1V 0.7 1 1.3 V

Enable Pull-Up Current Pin pulled up to 4.5V typically

when left unconnected 2 µA

Supply Current in Shutdown VEN = 0 8 20 µA

IC Supply Current in Operation VEN = 3V, VFB = 1.4V 0.7 mA

Thermal Shutdown Temperature Hysteresis = 10°C 160 °C

: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may

affect device reliability.

ACT4060

Innovative Products. Active Solutions. - 4 - www.active-semi.com

Rev8, 24-Jul-07

FUNCTIONAL BLOCK DIA GRAM

FUNCTIONAL DESCRIPTION

As seen in Functional Block Diagram, the ACT4060

is a current mode pulse width modulation (PWM)

converter. The converter operates as follows:

A switching cycle starts when the rising edge of the

Oscillator clock output causes the High-Side Power

Switch to turn on and the Low-Side Power Switch to

turn off. With the SW side of the inductor now con-

nected to IN, the inductor current ramps up to store

energy in the magnetic field. The inductor current

level is measured by the Current Sense Amplifier

and added to the Oscillator ramp signal. If the re-

sulting summation is higher than the COMP voltage,

the output of the PWM Comparator goes high.

When this happens or when Oscillator clock output

goes low, the High-Side Power Switch turns off and

the Low-Side Power Switch turns on. At this point,

the SW side of the inductor swings to a diode volt-

age below ground, causing the inductor current to

decrease and magnetic energy to be transferred to

output. This state continues until the cycle starts

again.

The High-Side Power Switch is driven by logic using

BS as the positive rail. This pin is charged to VSW +

6V when the Low-Side Power Switch turns on.

The COMP voltage is the integration of the error

between FB input and the internal 1.293V refer-

ence. If FB is lower than the reference voltage,

COMP tends to go higher to increase current to the

output. Current limit happens when COMP reaches

its maximum clamp value of 2.55V.

The Oscillator normally switches at 420kHz. How-

ever, if FB voltage is less than 0.7V, then the

switching frequency decreases until it reaches a

typical value of 50kHz at VFB = 0.5V.

Shutdown Control

The ACT4060 has an enable input EN for turning

the IC on or off. When EN is less than 0.7V, the IC

is in 8μA low current shutdown mode and output is

discharged through the Low-Side Power Switch.

When EN is higher than 1.3V, the IC is in normal

operation mode. EN is internally pulled up with a

2μA current source and can be left unconnected for

always-on operation. Note that EN is a low voltage

input with a maximum voltage of 6V, it should never

be directly connected to IN.

Thermal Shutdown

The ACT4060 automatically turns off when its junc-

tion temperature exceeds 160°C.

COMP

LOGIC

THERMAL

SHUTDOWN

REGULATOR

REFERENCE

OSCILLATOR

RAMP

FOLDBACK

CONTROL

1.293V

ERROR

AMPLIFIER

ENABLE

0.2Ω

HIGH-SIDE

POWER

SWITCH

+-+--

PWM

COMP

CURRENT SENSE

AMPLIFIER

4.7ΩLOW-SIDE

POWER SWITCH

ACT4060

Innovative Products. Active Solutions. - 5 - www.active-semi.com

Rev8, 24-Jul-07

Figure 1 shows the connections for setting the out-

put voltage. Select the proper ratio of the two feed-

back resistors RFB1 and RFB2 based on the output

voltage. Typically, use RFB2 ≈ 10kΩ and determine

RFB1 from the following equation:

The inductor maintains a continuous current to the

output load. This inductor current has a ripple that is

dependent on the inductance value: higher induc-

tance reduces the peak-to-peak ripple current. The

trade off for high inductance value is the increase in

inductor core size and series resistance, and the

reduction in current handling capability. In general,

select an inductance value L based on ripple current

requirement:

VOUT 1.5V 1.8V 2.5V 3.3V 5V

L 6.8μH 6.8μH 10μH 15μH 22μH

where IOUTMAX is the maximum output current, KRIP-

PLE is the ripple factor, RESR is the ESR of the output

capacitor, fSW is the switching frequency, L is the

inductor value, and COUT is the output capacitance.

In the case of ceramic output capacitors, RESR is

very small and does not contribute to the ripple.

Therefore, a lower capacitance value can be used

for ceramic type. In the case of tantalum or electro-

lytic capacitors, the ripple is dominated b y RESR

multiplied by the ripple current. In that case, the

output capacitor is chosen to have sufficiently low

ESR.

For ceramic output capacitor, typically choose a

capacitance of about 22µF. For tantalum or electro-

lytic capacitors, choose a capacitor with less than

50mΩ ESR.

Rectifier Diode

Use a Schottky diode as the rectifier to conduct cur-

rent when the High-Side Power Switch is off. The

Schottky diode must have current rating higher than

the maximum output current and a reverse voltage

rating higher than the maximum input voltage.

Inductor Selection

APPLICATIONS INFORMATION

where VIN is the input voltage, VOUT is the output

voltage, fSW is the switching frequency, IOUTMAX is

the maximum output current, and KRIPPLE is the rip-

ple factor. Typically, choose KRIPPLE = 30% to corre-

spond to the p eak-to-peak ripple current being 30%

of the maximum output current.

With this inductor value, the peak inductor current is

IOUT × (1 + KRIPPLE/2). Make sure that this peak in-

ductor current is less that the 3A current limit. Fi-

nally, select the inductor core size so that it does

not saturate at 3A. Typical inductor values for vari-

ous output voltages are shown in Table 1.

(1)

(2)

Figure 1:

Output Voltage Setting











 1

V293.1V

RR OUT

2FB1FB





RIPPLEOUTMAXSWIN

OUTINOUT KIfV VVV

L



(3)

ESRRIPPLEOUTMAXRIPPLE RKIV 

OUT

INLCf28 V





Input Capacitor

The input capacitor needs to be carefull y selected

to maintain sufficiently low ripple at the supply input

of the converter. A low ESR capacitor is highly rec-

ommended. Since large current flows in and out of

this capacitor during switching, its ESR also affects

efficiency.

The input capacitance needs to be higher than

10µF. The best choice is the ceramic type, how-

ever, low ESR tantalum or electrolytic types may

also be used provided that the RMS ripple current

rating is higher than 50% o f the output current. The

input capacitor should be placed close to the IN and

G pins of the IC, with the shortest traces possible.

In the case of tantalum or electrolytic types, they

can be further a way if a small parallel 0.1µF ce-

ramic capacitor is placed right next to the IC.

Output Capacitor

The output capacitor also needs to have low ESR to

keep low output voltage ripple. The output ripple

voltage is:

Output Voltage Setting

RFB1

RFB2

VOUT

ACT4060

Table 1:

Typical Inductor Values

ACT4060

Innovative Products. Active Solutions. - 6 - www.active-semi.com

Rev8, 24-Jul-07

STABILITY COMPENSATION STEP 2. Set the zero fZ1 at 1/4 of the cross over

frequency. If RCOMP is less than 15kΩ, the equation

for CCOMP is:

If RCOMP is limited to 15kΩ, then the actual cross

over frequency is 3.4 / (VOUTCOUT). Therefore:

STEP 3. If the output capacitor’s ESR is high

enough to cause a zero at lower than 4 times the

cross over f requency, an additional compensation

capacitor CCOMP2 is required. The condition for using

CCOMP2 is:

And the proper value for CCOMP2 is:

Though CCOMP2 is unnecessary when the output ca-

pacitor has sufficiently low ESR, a small value

CCOMP2 such as 100pF may improve stability against

PCB layout parasitic effects.

Table 2 shows some calculated results based on

the compensation method above.

Table 2:

Typical Compensation for Different Output

Voltages and Output Capacitors

VOUT COUT RCOMP CCOMP CCOMP2

2.5V 22μF Ceramic 8.2kΩ 2.2nF None

3.3V 22μF Ceramic 12kΩ 1.5nF None

5V 22μF Ceramic 15kΩ 1.5nF None

2.5V 47μF SP CAP 15kΩ 1.5nF None

3.3V 47μF SP CAP 15kΩ 1.8nF None

5V 47μF SP CAP 15kΩ 2.7nF None

2.5V 470μF/6.3V/30mΩ 15kΩ 15nF 1nF

3.3V 470μF/6.3V/30mΩ 15kΩ 22nF 1nF

5V 470μF/6.3V/30mΩ 15kΩ 27nF None

: CCOMP2 is needed for high ESR output capacitor.

Figure 3 s hows an example ACT4060 application circuit generat-

ing a 2.5V/2A output.

COMP

ESRCOUTOUT

2COMP R

C(13)

Figure 2:

Stability Compensation

(10)

(F)

COMP

COMP R108.1

C





(11)

(F)

OUTOUT

COMP CV102.1C 



: CCOMP2 is needed only for high ESR output capacitor

The feedback loop of the IC is stabilized by the

components at the COMP pin, as shown in Figure 2.

The DC loop gain of the system is determined by

the following equation:

The dominant pole P1 is due to CCOMP:

And finally, the third pole is due to RCOMP and

CCOMP2 (if CCOMP2 is used):

The following steps should be used to compensate

the IC:

STEP 1. Set the cross over frequency at 1/10 of the

switching frequency via RCOMP:

but limit RCOMP to 15kΩ maximum.

The first zero Z1 is due to RCOMP and CCOMP:

The second pole P2 is the output pole:

COMP2COMP

3P CRπ21

f(8)

(Ω) (9)

V3.1GG10 fCVπ2

RCOMPEA

SWOUTOUT

COMP 



OUTOUT

8CV107.1 

(4)

COMPVEA

OUT

VDC GA

IV3.1

A

(5)

COMPVEA

1P CAπ2G

f

(6)

OUTOUT

OUT

2P CVπ2I

f

(12)

(Ω)



















OUT

ESRCOUT V012.0,

C101.1

MinR

(7)

COMP2COMP

1Z CRπ21

f

ACT4060

Innovative Products. Active Solutions. - 7 - www.active-semi.com

Rev8, 24-Jul-07

Figure 3:

ACT4060 2.5V/2A Output Application

: D1 is a 40V, 3A Schottky diode with low forward voltage, an IR 30BQ040 or SK34 equivalent. C4 can be either a ceramic capacitor

(Panasonic ECJ-3YB1C226M) or SP-CAP (Specialty Polymer) Aluminum Electrolytic Capacitor such as Panasonic EEFCD0J470XR.

The SP-Cap is based on aluminum electrolytic capacitor technology, but uses a solid polymer electrolyte and has very stable capaci-

tance characteristics in both operating temperature and frequency compared to ceramic, polymer, and low ESR tantalum capacitors.

ACT4060

Innovative Products. Active Solutions. - 8 - www.active-semi.com

Rev8, 24-Jul-07

TYPICAL PERFORMANCE CHARACTERISTICS

Input Voltage (V)

5 10 15 20

ACT4060-002

Switching Frequency vs. Input Voltage

390

410

370

Switching Frequency (kHz)

430

450

-40 Junction Temperature (°C)

0 40 80 120

ACT4060-001

1.29

1.33

1.31

1.27

1.25

Feedback Voltage (V)

Feedback Voltage vs. Junction Temperature

(Circuit of Figure 3, unless otherwise specified.)

Output Current (A)

Efficiency (%)

ACT4060-003

0.1 0.5 0.9 1.3

Efficiency vs. Output Current

1.7

VIN = 7V

VOUT = 5V

ACT4060

Innovative Products. Active Solutions. - 9 - www.active-semi.com

Rev8, 24-Jul-07

Active-Semi, Inc. reserves the right t o modify the circuitry or specifications wit hout notice. Users should evaluate each

product to make sure that it is suitable for their applications. Active-Semi products are not intended o r authorized for use

as critical components in life-support devices or systems. Active-Semi, Inc. does not assume any liability arising out of

the use of any product or circuit described in this datasheet, nor does it convey any patent license.

Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and o ther products, contact

sales@active-semi.com or visit http://www.active-semi.com. For other inquiries, please send to:

1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA

PACKAGE OUTLINE

SOP-8 PACKAGE OUTLINE AND DIMENSIONS

SYMBOL DIMENSION IN

MILLIMETERS DIMENSION IN

INCHES

MIN MAX MIN MAX

A 1.350 1.750 0.053 0.069

A1 0.100 0.250 0.004 0.010

A2 1.350 1.550 0.053 0.061

B 0.330 0.510 0.013 0.020

C 0.190 0.250 0.007 0.010

D 4.700 5.100 0.185 0.201

E 3.800 4.000 0.150 0.157

E1 5.800 6.300 0.228 0.248

e 1.270 TYP 0.050 TYP

L 0.400 1.270 0.016 0.050

θ 0° 8° 0° 8°