ISL6532AEVAL1 Intersil, ISL6532AEVAL1 Datasheet - Page 12

• Manufacturer Part Number: ISL6532AEVAL1
• Description: EVALUATION BOARD 1 ISL6532A
• Manufacturer: Intersil

Specifications of ISL6532AEVAL1

• Main Purpose: Special Purpose DC/DC, DDR Memory Supply
• Outputs And Type: 3, Non-Isolated
• Voltage - Output: 1.25V, 1.5V, 2.5V
• Voltage - Input: 5V, 12V
• Regulator Topology: Buck
• Frequency - Switching: 250kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ISL6532A
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Power - Output: -

Application Guidelines
Layout Considerations
Layout is very important in high frequency switching
converter design. With power devices switching efficiently at
250kHz, the resulting current transitions from one device to
another cause voltage spikes across the interconnecting
impedances and parasitic circuit elements. These voltage
spikes can degrade efficiency, radiate noise into the circuit,
and lead to device overvoltage stress. Careful component
layout and printed circuit board design minimizes these
voltage spikes.
As an example, consider the turn-off transition of the control
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 ISL6532A
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
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
ISL6532A first. Minimize the length of the connections between
the input capacitors, C
them nearby. Position both the ceramic and bulk input
capacitors as close to the upper MOSFET drain as possible.
IN
, and the power switches by placing
12
IN
and C
OUT
could each
TT
ISL6532A
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 5 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
The PWM wave is smoothed by the output filter (L
OUT
FIGURE 4. PRINTED CIRCUIT BOARD POWER PLANES
12V
KEY
) is regulated to the Reference voltage level. The error
ATX
ISL6532A
GND PAD
VIA CONNECTION TO GROUND PLANE
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT PLANE LAYER
P12V
VDDQ(3)
P5VSBY
DRIVE2
LGATE
5VSBY
PHASE
UGATE
AND ISLANDS
VTT(2)
GNDP
COMP
GNDP
NCH
FB2
FB
E/A
) is compared with the oscillator (OSC)
C
C
BP
OUT2
R
C
C
2
2
BP
R
IN
5VSBY
R
6
4
at the PHASE node.
R
C
5
1
C
3
R
V
V
Q
Q
1
DDQ
TT
R
1
V
2
3
C
IN_DDR
L
OUT3
Q
OUT
C
3
C
IN
OUT1
V
V
IN_AGP
AGP
O
V
DDQ
and C
May 5, 2008
FN9099.5
O
).