ISL6529A Datasheet, PDF (13/15 Pages) Intersil Corporation – Dual Regulator.Synchronous Rectified Buck PWM and Linear Power Controller

ISL6529A
Ensure that the MOSFET is within its maximum junction
temperature at high ambient temperature by calculating the
temperature rise according to package thermal-resistance
specifications. A separate heatsink may be necessary
depending upon MOSFET power, package type, ambient
temperature, air flow, and load current requirements.
The gate drive to the switching transistors ranges from
slightly below 12V to ground. Because of the large voltage
swing, logic-level transistors are not necessary in this
application.
However, if logic-level transistors or transistors with low
V_GS(on) are used, close attention to layout guidelines should
be exercised, as the low gate threshold could lead to some
shoot-through despite counteracting circuitry present aboard
the ISL6529A.
N-Channel MOSFET Transistor Selection
The main criteria for selection of the linear regulator pass
transistor is package selection for efficient removal of heat.
Select a package and heatsink that maintains the junction
temperature below the rating with a maximum expected
ambient temperature.
The power dissipated in the linear regulator is:
P_LINEAR ≅ I_O × (V_IN – V_OUT)
(EQ. 18)
where I_O is the maximum output current and V_OUT is the
nominal output voltage of the linear regulator.
Linear Regulator Output Capacitors
The output capacitors for the linear regulator provide
dynamic load current. Output capacitors should be selected
for transient load regulation.
ISL6529A Converter Application Circuit
L2
+3.3V
1µH
C7
1000µF
+5V
+12V
C6
470µF
C8
4.7µF
C5
1µF
C15
1µF
Q3
R13
5VCC
DRIVE2
12VCC _UGATE
1.0kΩ
C4
470pF
ISL6529A _LGATE
VOUT2
(1A)
R12
R5
6.8kΩ
COMP
2.5V
4.64kΩ
FB2
GND
FB
PGND
C14
C12
R6
1µF
1500µF ^2.15kΩ
Q1, Q2
Q3
L1
L2
IRF7313
MTD3055V
919AS-4R7M
919AS-1R0N
IR
Fairchild
TOKO
TOKO
Q1
L1
Q2 4.7µH
C9
470µF
C1
47nF
R2
10.7kΩ
C2
1.2nF
R1
1.0kΩ
VOUT1
(6A)
1.6V
C10
1µF
R4
1.0kΩ
R3
C3
10Ω 47nF
FIGURE 9. POWER SUPPLY APPLICATION CIRCUIT FOR A GRAPHICS CONTROLLER
13
FN9127.1
December 28, 2004