AIC2511-50PM5TB 查看數據表（PDF） - Analog Intergrations

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AIC2511-50PM5TB

3A STEP-DOWN PWM CONVERTER

Analog Intergrations 

AIC2511

APPLICATION INFORMATION (Continued)

Components Selection

Assume the input voltage is 12V, output voltage is

5V and maximum load current is 3A. The output

Inductor

ripple must be smaller than 2% of output voltage

The inductor selection depends on the operating

frequency of the AIC2511. The ripple current ∆IL

interrelates with inductor value. A lower inductor

value gets a higher ripple current. Besides, a

higher VIN or VOUT can also get the same result.

The inductor value can be calculated as the

Inductor selection

L

=

(f

1

)(∆I L )VOUT

⎜⎜⎝⎛1 −

VOUT

VIN

⎟⎟⎠⎞

= 1 × 5 × ⎜⎛1 − 5 ⎟⎞ = 32.4uH

150k × 0.6 ⎝ 12 ⎠

following formula.

L

=

1

(f )(∆IL

)

VOUT ⎜⎜⎝⎛1−

VOUT

VIN

⎟⎟⎠⎞

Here, the delta IL is 0.6A. So we choose 33uH

inductor.

Users can define the acceptable ∆IL to gain a

suitable inductor value.

Diode

The diode current rating must be higher than 1.3

times maximum load current. Also, if the power

supply needs to resist a continuous output short,

the diode should have a current ration equal to the

maximum current limit of the AIC2511. The

reverse voltage rating of the diode should be

higher than 1.25 times input voltage and the diode

must be fast. The reverse recovery time of the

diode is short.

Capacitor

The selection of output capacitor depends on the

suitable ripple voltage. Lower ripple voltage

corresponds to lower ESR (Equivalent Series

Resistor) of output capacitor. Typically, once the

ESR is satisfied with the ripple voltage, the value

of capacitor is adequate for filtering. The formula

of ripple voltage is as below:

∆VOUT

=

∆IL ⎜⎜⎝⎛ESR +

1

8fCOUT

⎟⎟⎠⎞

The typical input capacitor is 470uF. But as the

temperature decreases, the input capacitor needs

to increase to stabilize the circuit.

Output capacitor selection

∆VOUT

=

∆I

L

⎜⎜⎝⎛

ESR

+

8

1

fCOUT

⎟⎟⎠⎞ < 100mV

We choice the capacitor value: ESR=0.12,

capacitance=220uF

⇒

∆VOUT

=

∆I L

⎜⎜⎝⎛ ESR+

8

1

fCOUT

⎟⎟⎠⎞

=

74mV

< 100mV

The full load is 3A and delta IL is 0.6A, so the

diode current rating must be higher than 3.6A.

CF Capacitor for adj version

As using the AIC2511 adj version, the CF

capacitor is required to provide additional stability.

In different condition, the CF capacitor must be

changed to make the circuit stable.

Output

Input

R1 R2 CF

Voltage (V) Voltage (V) (Ω) (Ω) (pF)

1.8

7

36k 82k 1000

4

12

180k 82k 360

6

12

180k 47k 360

8

15

180k 33k 360

10

18

150k 22k 470

15

25

110k 10k 560

Table 1

Example

9

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