APW7176AQBI-TRG 查看數據表（PDF） - Anpec Electronics

零件编号

产品描述 (功能)

生产厂家

APW7176AQBI-TRG

Dual 1.5MHz, 1A Synchronous Step-Down Converter

Anpec Electronics 

APW7176A

Application Information (Cont.)

Output Capacitor Selection

The output voltage ripple is a significant parameter to

estimate the performance of a convertor. There are two

discrete components that affect the output voltage ripple

to be bigger or smaller. It is recommended to use the

criterion mentioned in the "Inductor Selection" to choose

a suitable inductor. Then, based on this known inductor

current ripple, the value and equivalent-series-resistance

(ESR) of output capacitor will affect the output voltage ripple

to be smaller or larger. The output voltage ripple consists

of two portions, one is the product of ESR and inductor

current ripple, the other portion is the function of the in-

ductor current ripple and the output capacitance. Figure-3

illustrates the waveform of the ripple voltage which is

generated when the inductor ripple current charges or

discharges the pure capacitor without the ESR.

0A

∆IL

I(COUT)

0.5TS

∆VOUT1

VOUT

Figure-3

Evaluate the ∆VOUT1 by the ideal of energy equalization.

According to the definition of Q,

Q

=

1

2





1

2

∆IL

⋅

1

2

TS





=

COUT

⋅ ∆VOUT1

....(6)

where TS is the inverse of switching frequency and the ∆IL

is the inductor current ripple. Move the COUT to the left side

to estimate the value of ∆VOUT1 as equation (7).

∆VOUT1

=

∆IL ⋅ TS

8 ⋅ COUT

................................(7)

As mentioned above, one part of output voltage ripple is

the product of the inductor current ripple and ESR of out-

put capacitor. The equation (8) explains the output volt-

age ripple estimation.

∆VOUT

=

∆IL

⋅ ESR +

TS

8 ⋅ COUT

.................(8)

Thermal Consideration

APW7176A is a high efficiency switching converter, it

means less power loss transferred into heat. Due to the

on resistance difference between internal power

PMOSFET and NMOSFET, the power dissipation at high

duty cycle is greater than the low duty cycle. The worst

case in the dropout operation is the conduction loss dis-

sipate mainly on the internal power PMOSFET. The power

dissipation is nearly defined as:

[ ] ( ) ( ) PD = IOUT 2 RDS−P ⋅D + RDS−N ⋅ 1− D .......(9)

The APW7176A provides internal over-temperature

protection. When the junction temperature reaches 150

degrees centigrade, the APW7176 will turn off both inter-

nal power PMOSFET and NMOSFET. The estimation of

the junction temperature, TJ, is defined as:

TJ = PD ⋅ θJA............................................(10)

where the θJA is the thermal resistance of the package

utilized by the APW7176A.

Output Voltage Setting

Then APW7176A has the adjustable version for output

voltage setting by the users. A suggestion of maximum

value of R2 is 300kΩ to keep the minimum current that

provides enough noise rejection ability through the re-

sistor divider. The output voltage is programmed by the

equation as below:

VOUT

=

0.6 ⋅ 1+

R1

R2

...............................(11)

VOUT

APW7176A

R1

FB

R2

Copyright © ANPEC Electronics Corp.

10

Rev. A.1 - Oct., 2012

www.anpec.com.tw

Share Link: