RT9612A Datasheet, PDF (12/15 Pages) Richtek Technology Corporation – Synchronous-Rectified Buck MOSFET Driver

RT9612A/B
standard JEDEC 51-7 four-layer thermal test board. The
maximum power dissipation at T_A = 25°C can be calculated
by the following formulas :
P_D(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for
SOP-8 package
P_D(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W for
SOP-8 (Exposed Pad) package
P_D(MAX) = (125°C − 25°C) / (70°C/W) = 1.429W for
WDFN-8EL 3x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T_J(MAX) and thermal
resistance, θ_JA. The derating curves in Figure 5 allow the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
SOP-8
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
25
Four-Layer PCB
SOP-8 (Exposed Pad)
WDFN-8EL 3x3
50
75
100
125
Ambient Temperature (°C)
Figure 5. Derating Curve of Maximum Power Dissipation
Layout Consideration
Figure 6 shows the schematic circuit of a synchronous
buck converter to implement the RT9612A/B. The
converter operates from 5V to 12V of input Voltage.
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 GND directly. Furthermore, the
bootstrap capacitors (C_B) should always be placed as close
to the pins of the IC as possible.
V_IN
12V
L1
C1
V_CORE
Q1
L2
C3
Q2
C2
1
BOOT
CB
8 _UGATE
7 _PHASE
PHB83N03LT
12V
R1
VCC ⁴
C4
2
PWM PWM
PHB95N03LT ⁵ _LGATE
GND ⁶
Figure 6. Synchronous Buck Converter Circuit
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
is a registered trademark of Richtek Technology Corporation.
DS9612A/B-03 June 2012