ISL6522A Datasheet, PDF (11/13 Pages) Intersil Corporation – Buck and Synchronous Rectifier Pulse-Width Modulator (PWM) Controller

ISL6522A
V_CC less the input supply. For +5V main power and +12V_DC
for the bias, the gate-to-source voltage of Q1 is 7V. A logic-level
MOSFET is a good choice for Q1 and a logic-level MOSFET
can be used for Q2 if its absolute gate-to-source voltage rating
exceeds the maximum voltage applied to PV_CC.
Schottky Selection
Rectifier D2 is a clamp that catches the negative inductor
swing during the dead time between turning off the lower
MOSFET and turning on the upper MOSFET. The diode must
be a Schottky type to prevent the lossy parasitic MOSFET
body diode from conducting. It is acceptable to omit the diode
and let the body diode of the lower MOSFET clamp the
negative inductor swing, but efficiency will drop one or two
percent as a result. The diode's rated reverse breakdown
voltage must be greater than the maximum input voltage.
12V_CC
V_IN
RTN
C1-3
3x 680µF
ISL6522A DC-DC Converter Application
Circuit
Figure 11 shows a DC-DC converter circuit for a
microprocessor application, originally designed to employ
the HIP6006 controller. Given the similarities between the
HIP6006 and ISL6522A controllers, the circuit can be
implemented using the ISL6522A controller without any
modifications. Detailed information on the circuit, including a
complete bill of materials and circuit board description, can
be found in Application Note AN9722. See Intersil’s home
page on the web: http://www.intersil.com.
C17-18
2x 1µF
1206
ENABLE
C13
0.1µF
C12
1µF
R7
1206
10K
VCC
6
SS 3
14
MONITOR AND
PROTECTION
RT ₁
R1
SPARE
OSC
U1
ISL6522A
REF
C19
1000pF
2 OCSET ^R6
10 BOOT
9 UGATE
3.01K
Q1
8 ^PHASE
13 ^PVCC
--
FB 5 ⁺⁺
+
+
--
12 ^LGATE
Q2
11 PGND
4
7
R2
1K
C14
COMP
GND
JP1
33pF
C15
R5
0.01µF 15K
C16
COMP
TP1
R3
SPARE
R4
1K
SPARE
CR1
4148
PHASE
TP2
C20
0.1µF
L1
CR2
MBR
340
C6-9
4x 1000µF
V_OUT
RTN
Component Selection Notes:
C1-C3 - Three each 680µF 25W VDC, Sanyo MV-GX or equivalent.
C6-C9 - Four each 1000µF 6.3W VDC, Sanyo MV-GX or equivalent.
L1 - Core: micrometals T50-52B; winding: ten turns of 17AWG.
CR1 - 1N4148 or equivalent.
CR2 - 3A, 40V Schottky, Motorola MBR340 or equivalent.
Q1, Q2 - Fairchild MOSFET; RFP25N05
FIGURE 11. DC-DC CONVERTER APPLICATION CIRCUIT
11
FN9122.2
April 13, 2005