RT9618GSW 데이터 시트보기 (PDF) - Richtek Technology
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RT9618GSW Datasheet PDF : 12 Pages
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RT9618/A
This dissipation is a function of switching frequency and
total gate charge of the selected MOSFET. Figure 3 shows
the power dissipation test circuit. CL and CU are the UGATE
and LGATE load capacitors, respectively. The bootstrap
capacitor value is 0.01uF.
10
+12V
1N4148
CBOOT
1uF
+12V
1uF
5V
PWM
BOOT
VCC UGATE
RT9618/A
PHASE
OD
PWM LGATE
PGND
2N7002
CU
3nF
2N7002
20
CL
3nF
Figure 3. Test Circuit
Figure 4 shows the power dissipation of the RT9618/A as
a function of frequency and load capacitance. The value of
the CU and CL are the same and the frequency is varied
from 100kHz to 1MHz.
Power Dissipation vs. Frequency
1000
900
CU=CL=3nF
800
700
600
500
CU=CL=2nF
400
300
CU=CL=1nF
200
100
0
0
200
400
600
800
1000
Frequency (kHz)
Figure 4. Power Dissipation vs. Frequency
TJ = (160°C/W x 100mW) + 25°C = 41°C
(11)
where the ambient temperature is 25°C.
The method to improve the thermal transfer is to increase
the PCB copper area around the RT9618/A first. Then,
adding a ground pad under IC to transfer the heat to the
peripheral of the board.
Layout Consideration
Figure 5 shows the schematic circuit of a two-phase
synchronous buck converter to implement the RT9618/A.
The converter operates from 5V to 12V of VIN.
When layout the PCB, 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 should be very close.
Next, the trace from UGATE, and LGATE should also be
short to decrease the noise of the driver output signals.
PHASE 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 C4
should be connected to PGND directly. Furthermore, the
bootstrap capacitors (CB) should always be placed as close
to the pins of the IC as possible.
L1
VIN
12V 1.2uH
VCORE
C3
1500uF
C1
C2
1000uF
1uF
PHB83N03LT
Q1
L2
2uH
Q2
D1
1
CB
1uF BOOT VCC 4
8 UGATE
7 PHASE
5 LGATE
2
PWM
3
OD
PGND 6
PHB95N03LT
12V
R1
10
C4
1uF
PWM
5V
Figure 5. Two-Phase Synchronous Buck Converter Circuit
The operating junction temperature can be calculated from
the power dissipation curves (Figure 4). Assume
VCC =12V, operating frequency is 200kHz and the
CU=CL=1nF which emulate the input capacitances of the
high side and low side power MOSFETs. From Figure 4,
the power dissipation is 100mW. For RT9618/A, the
SOP-8 package thermal resistance θJA is 160° C/W, the
operating junction temperature is calculated as :
www.richtek.com
10
DS9618/A-06 April 2011
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