ISL6530/31EVAL1 INTERSIL [Intersil Corporation], ISL6530/31EVAL1 Datasheet - Page 11

• Manufacturer Part Number: ISL6530/31EVAL1
• Description: Dual 5V Synchronous Buck Pulse-Width Modulator (PWM) Controller for DDRAM Memory VDDQ and VTT Termination
• Manufacturer: INTERSIL [Intersil Corporation]

nodes. Use copper filled polygons on the top and bottom
circuit layers for the phase nodes. Use the remaining printed
circuit layers for small signal wiring. The wiring traces from
the GATE pins to the MOSFET gates should be kept short
and wide enough to easily handle the 1A of drive current.f
The switching components should be placed close to the
ISL6531 first. Minimize the length of the connections
between the input capacitors, C
by placing them nearby. Position both the ceramic and bulk
input capacitors as close to the upper MOSFET drain as
possible. Position the output inductor and output capacitors
between the upper MOSFET and lower diode and the load.
FIGURE 7. PRINTED CIRCUIT BOARD POWER PLANES
KEY
ISL6531
VIA CONNECTION TO GROUND PLANE
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT PLANE LAYER
UGATE1
UGATE2
PHASE1
PHASE2
LGATE1
SENSE1
LGATE2
SENSE2
COMP1
BOOT1
PGND1
BOOT2
PGND2
AND ISLANDS
GND
VCC
FB1
C
+5V V
BP
R
C
C
C
2A
PHASE2
2A
IN
PHASE1
D2
BOOT2
BOOT1
R4
+5V V
11
C
D1
IN
V
1A
IN
DDQ
C
, and the power switches
R
3A
Q1
Q2
Q3
Q4
1A
R
3A
L
L
C
OUT1
OUT2
IN
C
C
OUT1
OUT2
V
V
DDQ
TT
ISL6531
The critical small signal components include any bypass
capacitors, feedback components, and compensation
components. Position the bypass capacitor, C
VCC pin with a via directly to the ground plane. Place the
PWM converter compensation components close to the FB
and COMP pins. The feedback resistors for both regulators
should also be located as close as possible to the relevant
FB pin with vias tied straight to the ground plane as required.
V
This section discusses the feedback compensation of the
V
control loop for a synchronous-rectified buck converter. The
output voltage (V
level. The error amplifier (error amp) output (V
compared with the oscillator (OSC) triangular wave to
provide a pulse-width modulated (PWM) wave with an
amplitude of V
smoothed by the output filter (L
The modulator transfer function is the small-signal transfer
function of V
gain and the output filter (L
break frequency at F
the modulator is simply the input voltage (V
peak-to-peak oscillator voltage ∆V
Modulator Break Frequency Equations
DV
F
DDQ
DDQ
LC
FIGURE 8. VOLTAGE-MODE BUCK CONVERTER
OSC
=
----------------------------------------- -
2π x
regulator. Figure 8 highlights the voltage-mode
Feedback Compensation
OSC
COMPARATOR
OUT
L
1
ERROR
AMP
COMPENSATION DESIGN
O
DETAILED COMPENSATION COMPONENTS
IN
V
ISL6531
x C
PWM
E/A
/V
OUT
at the PHASE node. The PWM wave is
E/A
Z
+
O
-
FB
-
+
COMP
REFERENCE
LC
) is regulated to the Reference voltage
C
. This function is dominated by a DC
REFERENCE
2
and a zero at F
C
+
-
1
O
DRIVER
DRIVER
R
and C
F
Z
2
O
ESR
IN
and C
OSC
=
FB
O
Z
), with a double pole
------------------------------------------ -
2π x ESR x C
FB
O
.
ESR
PHASE
(PARASITIC)
).
V
C
IN
3
IN
L
Z
R
. The DC gain of
1
O
IN
1
) divided by the
BP
ESR
R
E/A
C
, close to the
3
O
V
OUT
O
) is
V
OUT