ISL6537CR Intersil, ISL6537CR Datasheet - Page 11

• Manufacturer Part Number: ISL6537CR
• Description: IC REG/CTRLR ACPI DUAL DDR 28QFN
• Manufacturer: Intersil

Specifications of ISL6537CR

• Applications: Memory, DDR/DDR2 Regulator
• Current - Supply: 7mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Supply: -

critical because they switch large amounts of energy, and
therefore tend to generate large amounts of noise. Next are
the small signal components which connect to sensitive
nodes or supply critical bypass current and signal coupling.
A multi-layer printed circuit board is recommended. Figure 2
shows the connections of the critical components in the
converter. Note that capacitors C
represent numerous physical capacitors. Dedicate one solid
layer, usually a middle layer of the PC board, for a ground
plane and make all critical component ground connections
with vias to this layer. Dedicate another solid layer as a
power plane and break this plane into smaller islands of
common voltage levels. Keep the metal runs from the
PHASE terminals to the output inductor short. The power
plane should support the input power and output power
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.
In order to dissipate heat generated by the internal V
LDO, the ground pad, pin 29, should be connected to the
internal ground plane through at least four vias. This allows
the heat to move away from the IC and also ties the pad to
the ground plane through a low impedance path.
The switching components should be placed close to the
ISL6537 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 and lower MOSFETs and the load.
The critical small signal components include any bypass
capacitors, feedback components, and compensation
components. Place the PWM converter compensation
components close to the FB and COMP pins. The feedback
resistors should be located as close as possible to the FB
pin with vias tied straight to the ground plane as required.
Feedback Compensation - PWM Buck Converter
Figure 3 highlights the voltage-mode control loop for a
synchronous-rectified buck converter. The output voltage
(V
amplifier output (V
triangular wave to provide a pulse-width modulated (PWM)
wave with an amplitude of V
PWM wave is 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 ΔV
OUT
) is regulated to the Reference voltage level. The error
OUT
/V
E/A
E/A
LC
) is compared with the oscillator (OSC)
. This function is dominated by a DC
and a zero at F
O
IN
11
and C
at the PHASE node. The
IN
IN
, and the power switches
OSC
and C
O
), with a double pole
ESR
.
OUT
IN
. The DC Gain of
) divided by the
O
could each
and C
TT
O
).
ISL6537
12V
FIGURE 2. PRINTED CIRCUIT BOARD POWER PLANES
KEY
ATX
ISL6537
GND PAD
VIA CONNECTION TO GROUND PLANE
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT AND/OR POWER PLANE LAYER
P12V
REFADJ4
VDDQ(2)
DRIVE2
LGATE
DRIVE4
DRIVE3
5VSBY
PHASE
UGATE
VTT(2)
COMP
GNDP
AND ISLANDS
FB2
FB4
FB3
FB
C
OUT2
R
C
C
C
2
2
BP
BP
R
R
5VSBY
R
8
6
4
R
C
R
7
1
5
C
3
R
5VDUAL
V
Q
Q
1
TT
R
1
2
3
Q
L
C
1
4
C
IN
OUT1
V
Q
Q
DDQ
5
3
C
V
C
OUT4
TT_GMCH/CPU
OUT4
V
DDQ
C
OUT3
V
July 18, 2007
GMCH
FN9142.6