RT9602GS RICHTEK [Richtek Technology Corporation], RT9602GS Datasheet - Page 7

• Manufacturer Part Number: RT9602GS
• Description: Dual Channel Synchronous-Rectified Buck MOSFET Driver
• Manufacturer: RICHTEK [Richtek Technology Corporation]

According to the design of RT9602, 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 "D
MOSFETs turned on
Before the low side MOSFET is turned on, the C
been charged to Vi. Thus, as C
g
It is helpful to calculate these currents in a typical case.
Assume a synchronous rectified BUCK converter, input
voltage V
is PHB83N03LT whose C
= 14nS. The low side MOSFET is PHB95N03LT whose
C
equation (1) and (2) we can obtain
DS9602-08 March 2007
2
iss
l
l
l
l
l
l
is charged up to 12V, the required current is
gs1
gs2
gd1
gd2
gs1
gs2
= 2200pF, C
= C
= C
=
= C
=
= C
1660 10
i
2200 10
gs1
g1
= 12V, V
gs2
gd2
dV
14 10
dV
30 10
dt
dV
dV
×
dt
dt
×
dt
×
×
g1
g2
= C
rss
2
= C
g1
-12
" had been turned on before high side
-12
=
-9
-9
=
= 500pF, and t
gd1
= V
×
×
C
gd2
12
C
12
gs1
g2
gs2
t
12V
iss
r1
t
Vi+12V
t
= 12V. The high side MOSFET
×
r1
= 1.428 (A)
= 0.88 (A)
r2
= 1660pF, C
12
×
t
r2
12
gd2
reverses its polarity and
r
= 30nS, from the
rss
= 380pF,and t
gd2
have
(2)
(3)
(1)
(4)
(5)
(6)
r
from equation. (3) and (4)
the total current required from the gate driving source is
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 RT9602. The
converter operates for the input rang from 5V to 12V.
Figure 2. Two- Phase Synchronous-Buck Converter Circuit
V
12V
CORE
Vin
I
I
l
l
gs1
gs2
g1
g2
1500uF
1500uF
C5
= I
1.2uH
= I
=
=
L1
C6
gs1 gd1
gs2
380 10
500 10
+I
C3
1000uF
+I
14 10
×
×
gd2
1000uF
C1
2uH
2uH
L2
L3
×
30 10
Q3
Q1
Q2
= (1.428+0.326) = 1.745(A)
-12
-12
= (0.88+0.4) = 1.28(A)
×
PHB83N03LT
PHB83N03LT
Q4
PHB95N03LT
-9
×
PHB95N03LT
×
1uF
1uF
C2
C4
12
(12+12)
-9
Cb2
1uF
Cb1
1uF
= 0.326 (A)
12
13
4
9
8
7
UGATE1
PHASE1
LGATE1
UGATE2
PHASE2
LGATE2
BOOT1
11
= 0.4(A)
RT9602
10
BOOT2
D1
PWM1
PWM2
PGND
VCC
PVCC
GND
D2
14
RT9602
5
1
2
3
6
www.richtek.com
1uF
C7
PWM1
PWM2
R1
10
(10)
(8)
(7)
(9)
12V
7