ISL6526CB Intersil, ISL6526CB Datasheet - Page 9

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ISL6526CB

Manufacturer Part Number
ISL6526CB
Description
IC CTRLR PWM SYNC BUCK 14-SOIC
Manufacturer
Intersil
Datasheet

Specifications of ISL6526CB

Pwm Type
Voltage Mode
Number Of Outputs
1
Frequency - Max
325kHz
Duty Cycle
100%
Voltage - Supply
2.97 V ~ 3.63 V
Buck
Yes
Boost
No
Flyback
No
Inverting
No
Doubler
No
Divider
No
Cuk
No
Isolated
No
Operating Temperature
0°C ~ 70°C
Package / Case
14-SOIC (3.9mm Width), 14-SOL
Frequency-max
325kHz
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

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(such as to other distributed loads on the rail or through a
voltage limiting protection device), the capacitance on this
rail will absorb the current. This situation will allow the
voltage level of the input rail to increase. If the voltage level
of the rail is boosted to a level that exceeds the maximum
voltage rating of any components attached to the input rail,
then those components may experience an irreversible
failure or experience stress that may shorten their lifespan.
Ensuring that there is a path for the current to flow other than
the capacitance on the rail will prevent this failure mode.
Application Guidelines
Layout Considerations
Layout is very important in high frequency switching
converter design. With power devices switching efficiently at
300kHz or 600kHz, 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
minimize the voltage spikes in the converters.
As an example, consider the turn-off transition of the PWM
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 minimize the magnitude of voltage spikes.
There are two sets of critical components in a DC/DC
converter using the ISL6526, ISL6526A. 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.
9
IN
and C
OUT
could each
ISL6526, ISL6526A
The switching components should be placed close to the
ISL6526, ISL6526A first. Minimize the length of the connections
between the input capacitors, C
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 MOSFET and the load.
The critical small signal components include any bypass
capacitors, feedback components, and compensation
components. Position the bypass capacitor, C
the 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.
Feedback Compensation
Figure 5 highlights the voltage-mode control loop for a
synchronous-rectified buck converter. The output voltage
(V
error amplifier (Error Amp) output (V
the oscillator (OSC) triangular wave to provide a pulse
width modulated (PWM) wave with an amplitude of V
OUT
FIGURE 4. PRINTED CIRCUIT BOARD POWER PLANES
ISL6526, ISL6526A
) is regulated to the Reference voltage level. The
CPVOUT
KEY
UGATE
PHASE
LGATE
AND ISLANDS
COMP
BOOT
GND
VCC
VIA CONNECTION TO GROUND PLANE
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT PLANE LAYER
FB
C
C
VCC
BP
R
C
C
2
2
BOOT
PHASE
R4
+3.3V V
IN
D1
C
1
, and the power switches by
C
IN
3
Q1
Q2
R
1
R
E/A
3
C
L
IN
OUT
) is compared with
C
OUT
BP
November 24, 2008
, close to
V
OUT
FN9055.10
IN
at

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