ISL6341 INTERSIL [Intersil Corporation], ISL6341 Datasheet - Page 13

• Manufacturer Part Number: ISL6341
• Description: 5V or 12V Single Synchronous Buck Pulse-Width Modulation (PWM) Controller
• Manufacturer: INTERSIL [Intersil Corporation]

.
Figure 11 shows the critical power components of the
converter. To minimize the voltage overshoot, the
interconnecting wires indicated by heavy lines should be part of
a ground or power plane in a printed circuit board. The
components shown should be located as close together as
possible. Please note that the capacitors C
represent numerous physical capacitors. For best results,
locate the ISL6341x within 1 inch of the MOSFETs, Q
The circuit traces for the MOSFET gate and source
connections from the ISL6341x must be sized to handle up to
2A peak current.
Figure 12 shows the circuit traces that require additional
layout consideration. Use single point and ground plane
construction for the circuits shown. Provide local V
decoupling between VCC and GND pins. Locate the
capacitor, C
PHASE pins. Locate the resistor, R
LGATE/OCSET pin because the internal current source is
only 10µA. Minimize any leakage current paths on the
COMP/EN pin. All components used for feedback
compensation and VOS resistor divider (inside the dotted
box) should be located as close to the IC as practical. Near
the load, pick a point V
run a single unloaded narrow trace from there to the
compensation components. The same trace can also be
used for VOS divider.
V
COMP/EN
FIGURE 11. PRINTED CIRCUIT BOARD POWER AND
C
FIGURE 12. PRINTED CIRCUIT BOARD SMALL SIGNAL
OUT
VCC
+V
LGATE/OCSET
CC
VOS
ISL6341x
VCC
FB
UGATE
PHASE
BOOT
ISL6341x
GND
GROUND PLANES OR ISLANDS
LAYOUT GUIDELINES
as close as practical to the BOOT and
OUT
LGATE/OCSET
BOOT
PHASE
C
BOOT
Q
V
Q
RETURN
that will be the regulation center;
R
2
IN
1
13
OCSET
+V
GD
OSCET
ISL6341, ISL6341A, ISL6341B, ISL6341C
C
IN
IN
L
+V
Q
Q
and C
close to the
O
1
2
IN
C
L
O
O
C
V
O
O
OUT
V
CC
may each
1
OUT
and Q
2
.
Feedback Compensation
This section highlights the design consideration for a
voltage-mode controller requiring external compensation. To
address a broad range of applications, a type-3 feedback
network is recommended, as shown in the top part of
Figure 13.
Figure 13 also highlights the voltage-mode control loop for a
synchronous-rectified buck converter, applicable to the
ISL6341x circuit. The output voltage (V
the reference voltage, V
(COMP pin voltage) is compared with the oscillator (OSC)
modified sawtooth wave to provide a pulse-width modulated
wave with an amplitude of V
PWM wave is smoothed by the output filter (L and C). The
output filter capacitor bank’s equivalent series resistance is
represented by the series resistor E.
The modulator transfer function is the small-signal transfer
function of V
gain, given by d
filter, with a double pole break frequency at F
F
channel inductance and its DCR, while C and E represent the
total output capacitance and its equivalent series resistance.
F
CE
LC
FIGURE 13. VOLTAGE-MODE BUCK CONVERTER
=
. For the purpose of this analysis, L and D represent the
CIRCUIT
---------------------------
2π
PWM
⋅
1
L C
COMP
OUT
⋅
COMPENSATION DESIGN
MAX
/V
HALF-BRIDGE
OSCILLATOR
COMP
V
OSC
ISL6341x
V
E/A
DRIVE
IN
R2
/V
REF
. This function is dominated by a DC
OSC
C2
F
+
-
VREF
CE
. The error amplifier output
IN
C1
, and shaped by the output
=
at the PHASE node. The
----------------------- -
2π C E
FB
UGATE
LGATE
PHASE
EXTERNAL CIRCUIT
⋅
1
⋅
R3
OUT
Ro
V
IN
R1
) is regulated to
LC
C3
L
and a zero at
December 2, 2008
V
D
OUT
C
E
FN6538.2
(EQ. 3)