VPA2000 datasheet(20/25 Pages) RENESAS

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VPA2000

Product Data

March 11, 2010

DESIGN EXAMPLE

To design a boost converter with VIN=3.3V, VOUT=8V,

IOUT=400mA, and assume the efficiency is 85%. Refer to

Figure 39, choose R8=4.99k . Use equation [2] to

calculate R7. Thus, R7=28k .

Inductor Selection

The value of the inductor will affect the boost converter

efficiency and output voltage ripple. A 4.7µH inductor

works for most applications.

The inductor current ripple should be around 40% of the

inductor current for a good compromise between the size

of inductor, cost, and power loss. Thus, the minimum

inductor value is calculated with the following equation:

























−













0.85

OUT

VDD

MIN

[8]

where fSW is the boost converter switching frequency

which is 1.2MHz. Therefore, LMIN=4.25µH, so choose a

4.7µH inductor.

Vendors usually provide inductor DC current value, IDC

and inductor saturated current value, ISAT. Choose the

inductor that offers both ratings at higher than the inductor

peak current level. Use the following equation to calculate

the inductor peak current:





































OUT

VDD

[9]

The calculated peak current level is 1.37A. The boost

converter current limit level should be higher than the

inductor peak current level. Connect RLIM pin to VIN to set

the current limit level to 2.35A (default value).

Diode Selection

A Schokkty diode should be chosen to reduce the power

loss of the diode. The diode current rating should be

higher than the output current level, and the reverse

breakdown voltage should be higher than the output

voltage.

Input Capacitor Selection

A 10µF or greater value input capacitor should be used.

Place a 4.7µF and 1µF capacitor close to the VIN1 pin and

VIN2 pin, respectively, to bypass the input voltage.

Ceramic capacitors should be chosen for their low ESR,

which greatly reduces the input voltage ripple.

Output Capacitor Selection

The value of output capacitor helps to reduce output

voltage ripple as well as to stabilize the boost converter. A

total of 20µF output capacitance is suitable for most

applications.

The output voltage ripple is affected by the ESR of the

output capacitor (∆VESR) as well as the variations in the

charge stored in the output capacitors (∆VC). However,

since ceramic capacitor ESR is fairly low, the output

voltage ripple is mainly affected by ∆VC, and the estimated

output voltage ripple is:

























−

∆V

OUT

VDD

[10]

Table 14. VPA2000 Components Selection

CIRCUIT 1

CIRCUIT 2

CIRCUIT 3

VIN

3.3V

AVDD

9.7V

12V

16V

IOUT

400mA

200mA

4.7µH

6.8µH

5.6µH

CAVDD

20µF

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