RT9607 datasheet(12/15 Pages) RICHTEK

12 / 15 page

RT9607/A

DS9607/A-07 April 2011

www.richtek.com

According to the design of RT9607/A, before driving the

gate of the high side MOSFET up to 12V (or 5V), the low

side MOSFET has to be off; and the high side MOSFET

is turned off before the low side is turned on. From Figure

1, the body diode

2" had been turned on before high

side MOSFETs turned on

Before the low side MOSFET is turned on, the Cgd2 have

been charged to Vi. Thus, as Cgd2 reverses its polarity

and g2 is charged up to 12V, the required current is

It is helpful to calculate these currents in a typical case.

Assume a synchronous rectified BUCK converter, input

voltage Vi = 12V, Vg1 = Vg2 = 12V. The high side MOSFET

is PHB83N03LT whose Ciss = 1660pF, Crss = 380pF,and tr

= 14nS. The low side MOSFET is PHB95N03LT whose

Ciss = 2200pF, Crss = 500pF, and tr = 30nS, from the

equation (1) and (2) we can obtain

the total current required from the gate driving source is

Ig1 = Igs + Igd1 = (1.428 + 0.326) = 1.745A

(9)

Ig2 = Igs2 + Igd2 = (0.88 + 0.4) = 1.28A

(10)

By a similar calculation, we can also get the sink current

required from the turned off MOSFET.

Layout Consider

Figure 2. shows the schematic circuit of a two-phase

synchronous-buck converter to implement the

RT9607/A. The converter operates for the input rang from

5V to 12V.

When layout the PC board, it should be very careful. The

power-circuit section is the most critical one. If not

configured properly, it will generate a large amount of EMI.

The junction of Q1, Q2, L2 and Q3, Q4, L4 should be very

close. The connection from Q1, and Q3 drain to positive

sides of C1, C2, C3, and C4; the connection from Q2, and

Q4 source to the negative sides of C1, C2, C3, and C4

should be as short as possible.

Next, the trace from Ugate1, Ugate2, Lgate1, and Lgate2

should also be short to decrease the noise of the driver

output signals. Phase1 and phase2 signals from the

junction of the power MOSFET, carrying the large gate

drive current pulses, should be as heavy as the gate drive

trace. The bypass capacitor C7 should be connected to

PGND directly. Furthermore, the bootstrap capacitors (Cb1,

Cb2) should always be placed as close to the pins of the

IC as possible.

Select the Bootstrap Capacitor

Figure 3. shows part of the bootstrap circuit of RT9607/A.

The VCB (the voltage difference between BOOT1 and

PHASE1 on RT9607/A) provides a voltage to the gate of

the high side power MOSFET. This supply needs to be

ensured that the MOSFET can be driven. For this, the

capacitance CB has to be selected properly. It is

In Figure 1, the current Ig1 and Ig2 are required to move the

gate up to 12V.The operation consists of charging Cgd

and Cgs. Cgs1 and Cgs2 are the capacitances from gate to

source of the high side and the low side power MOSFETs,

respectively. In general data sheets, the Cgs is referred as

“C

iss” which is the input capacitance. Cgd1 and Cgd2 are

the capacitances from gate to drain of the high side and

the low side power MOSFETs, respectively and referred

to the data sheets as "Crss," the reverse transfer

capacitance. For example, tr1 and tr2 are the rising time of

the high side and the low side power MOSFETs

respectively, the required current Igs1 and Igs2, are showed

below

gs2

gs1

(1)

(2)

0.88A

2200

1.428A

1660

gs2

-12

gs1

(6)

(5)

gd2

12V

(4)

gd1

12V

(3)

0.4A

12)

(12

500

0.326A

380

gs2

-12

gs1

(8)

(7)

from equation. (3) and (4)

RT9607 датащи(PDF) 12 Page - Richtek Technology Corporation

RT9607 датащи(HTML) 12 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

датащи скачать

ссылки URL