ISL6532BCR Intersil, ISL6532BCR Datasheet - Page 10

• Manufacturer Part Number: ISL6532BCR
• Description: IC REG/CTRLR ACPI DUAL DDR 20QFN
• Manufacturer: Intersil

Specifications of ISL6532BCR

• Applications: Memory, DDR/DDR2 Regulator
• Current - Supply: 5.25mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Supply: -

spikes can degrade efficiency, radiate noise into the circuit,
and lead to device over-voltage stress. Careful component
layout and printed circuit board design minimizes these
voltage spikes.
As an example, consider the turn-off transition of the upper
MOSFET. Prior to turn-off, the MOSFET is carrying the full
load current. During turn-off, current stops flowing in the
MOSFET and is picked up by the lower MOSFET. Any
parasitic inductance in the switched current path generates a
large voltage spike during the switching interval. Careful
component selection, tight layout of the critical components,
and short, wide traces minimizes the magnitude of voltage
spikes.
There are two sets of critical components in the ISL6532B
switching converter. The switching components are the most
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 4
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
the ground pad, pin 21, 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
ISL6532B 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.
10
IN
IN
, and the power switches
and C
OUT
could each
TT
LDO,
ISL6532B
Feedback Compensation - PWM Buck Converter
Figure 5 highlights the voltage-mode control loop for a
synchronous-rectified buck converter. The output voltage
(V
error amplifier output (V
(OSC) triangular wave to provide a pulse-width modulated
(PWM) wave with an amplitude of V
The 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 ∆V
Modulator Break Frequency Equations
F LC
OUT
FIGURE 4. PRINTED CIRCUIT BOARD POWER PLANES
12V
=
KEY
ATX
) is regulated to the Reference voltage level. The
------------------------------------------ -
2π x
ISL6532B
GND PAD
VIA CONNECTION TO GROUND PLANE
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT PLANE LAYER
P12V
VDDQ(2)
P5VSBY
OUT
L O x C O
1
LGATE
5VSBY
UGATE
AND ISLANDS
VTT(2)
COMP
NCH
GND
GND
/V
FB
E/A
LC
C
C
BP
. This function is dominated by a DC
OUT2
and a zero at F
E/A
R
C
C
2
2
BP
O
) is compared with the oscillator
5VSBY
R
F ESR
4
and C
C
1
C
OSC
3
=
R
V
V
O
Q
Q
1
IN
DDQ
TT
------------------------------------------- -
2π x ESR x C O
R
), with a double pole
1
V
2
3
.
ESR
IN_DDR
at the PHASE node.
L
OUT
C
C
IN
IN
. The DC Gain of
OUT1
1
) divided by the
V
O
DDQ
and C
O
).