PCMB065T-2R2MS datasheet(16/22 Pages) IRF

16 / 22 page

March 27, 2013 | V2.2 | PD97601

IR3473

6A Highly Integrated SupIRBuck

DESIGN EXAMPLE

DESIGN CRITERIA

• Input Voltage, VIN = 6V to 21V

• Output Voltage, VOUT = 1.25V

• Switching Frequency, Fs = 400kHz

• Inductor Ripple Current, 2ΔI = 2A

• Maximum Output Current, IOUT = 6A

• Over Current Trip, IOC = 9A

• Current Transient Step Size = 3A

• Overshoot Allowance, VOS = VOUT + 50mV

• Undershoot Allowance, VDROP = 50mV

Find RFF:

Pick a standard value 158 kΩ, 1% resistor.

Find RSET:

Pick a 11.5kΩ, 1% standard resistor.

Find a resistive voltage divider for VOUT = 1.25V:

R2 = 1.33kΩ, R1 = 1.96 kΩ, both 1% standard resistors.

Choose the soft start capacitor:

Once the soft start time has chosen, such as 1000µs to

reach to the reference voltage, a 22nF for CSS is used to

meet 1000µs.

Choose an inductor to meet the design specification:

Choose the inductor with the lowest DCR and AC power

loss as possible to increase the overall system efficiency.

For instance, choose a PCMB065T‐1R5MS manufactured by

CYNTEC. The inductance of this part is 1.5µH and has 6.7mΩ

DCR. Ripple current needs to be recalculated using the chosen

inductor.

Choose an input capacitor:

A Panasonic 10µF (ECJ3YB1E106M) accommodates 6 Arms of

ripple current at 300kHz. Due to the chemistry of multilayer

ceramic capacitors, the capacitance varies over temperature

and operating voltage, both AC and DC. One 10µF capacitor is

recommended. In a practical solution, one 1µF capacitor is

required along with 10µF. The purpose of the 1µF capacitor is

to suppress the switching noise and deliver high frequency

current.

Choose an output capacitor:

To meet the undershoot and overshoot specification,

equations 7b and 8 will be used to calculate the minimum

output capacitance. As a result, 110μF will be needed for 3A

load removal. To meet the stability requirement, choose an

output capacitor with ESR larger than 9mΩ. Combine those

two requirements, one can choose a set of output capacitors

from manufactures such as SP‐Cap (Specialty Polymer

Capacitor) from Panasonic or POSCAP from Sanyo. A 150μF

(4TPE150MI) from Sanyo with 18mΩ ESR will meet both

requirements.

If an all ceramic output capacitor solution is desired, the

external slope injection circuit composed of R6, C13, and C14

is required as explained in the Stability Considerations

section. In this design example, we can choose C14 = 1nF and

C13 = 100nF. To calculate the value of R6 with PCMB065T‐

1R5MS as our inductor:

Pick a standard value for R6 = 2.26kΩ.

156

400k

1.25

RFF

⋅

24m

RSET

0.5

OUT

⋅

()

1.5

400k

1.25

ΔI

OUT

⋅

−

(

)

400k

1.5

1.25

2Δ

⋅

1.25

IN_RMS

⎟

⎠

⎞

⎜

⎝

⎛

⋅

DCR

100

PCMB065T-2R2MS датащи(PDF) 16 Page - International Rectifier

PCMB065T-2R2MS датащи(HTML) 16 Page - International Rectifier

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

датащи скачать

ссылки URL