ISL6526EVAL2

Manufacturer Part NumberISL6526EVAL2
DescriptionEVALUATION BOARD QFN ISL6526
ManufacturerIntersil
ISL6526EVAL2 datasheet
 


Specifications of ISL6526EVAL2

Main PurposeDC/DC, Step DownOutputs And Type1, Non-Isolated
Voltage - Output2.5VCurrent - Output5A
Voltage - Input3.3 ~ 5VRegulator TopologyBuck
Frequency - Switching300kHzBoard TypeFully Populated
Utilized Ic / PartISL6526Lead Free Status / RoHS StatusContains lead / RoHS non-compliant
Power - Output-  
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input voltage and a voltage rating of 1.5 times is a
conservative guideline. The RMS current rating requirement
for the input capacitor of a buck regulator is approximately
1/2 the DC load current.
The maximum RMS current required by the regulator may be
closely approximated using Equation 15:
V
1
2
OUT
×
×
I
=
------------- -
I
+
----- -
RMS
OUT
V
12
MAX
MAX
IN
For a through hole design, several electrolytic capacitors may
be needed. For surface mount designs, solid tantalum
capacitors can be used, but caution must be exercised with
regard to the capacitor surge current rating. These capacitors
must be capable of handling the surge-current at power-up.
Some capacitor series available from reputable manufacturers
are surge current tested.
MOSFET Selection/Considerations
The ISL6526, ISL6526A require two N-Channel power
MOSFETs. These should be selected based upon r
gate supply requirements, and thermal management
requirements.
In high-current applications, the MOSFET power dissipation,
package selection and heatsink are the dominant design
factors. The power dissipation includes two loss components;
conduction loss and switching loss. The conduction losses are
the largest component of power dissipation for both the upper
and the lower MOSFETs. These losses are distributed
between the two MOSFETs according to duty factor. The
switching losses seen when sourcing current will be different
from the switching losses seen when sinking current. When
sourcing current, the upper MOSFET realizes most of the
switching losses. The lower switch realizes most of the
switching losses when the converter is sinking current (see
Equations 16 and 17). These equations assume linear
voltage-current transitions and do not adequately model
power loss due the reverse-recovery of the upper and lower
MOSFET’s body diode. The gate-charge losses are
dissipated by the ISL6526, ISL6526A and don't heat the
MOSFETs. However, large gate-charge increases the
switching interval, t
which increases the MOSFET
SW
switching losses. Ensure that both MOSFETs are within their
maximum junction temperature at high ambient temperature
by calculating the temperature rise according to package
thermal-resistance specifications. A separate heatsink may be
necessary depending upon MOSFET power, package type,
ambient temperature and air flow.
Losses while Sourcing Current
1
2
×
×
-- - Io
P
=
Io
r
D
+
(
)
UPPER
DS ON
2
2
P
= Io
x r
x (1 - D)
LOWER
DS(ON)
12
ISL6526, ISL6526A
Losses while Sinking Current
P
UPPER
P
LOWER
2
V
V
V
IN
OUT
×
OUT
---------------------------- -
------------- -
×
L
f
V
Given the reduced available gate bias voltage (5V), logic-level
s
IN
or sub-logic-level transistors should be used for both
(EQ. 15)
N-MOSFETs. Caution should be exercised with devices
exhibiting very low V
protection present aboard the ISL6526, ISL6526A may be
circumvented by these MOSFETs if they have large parasitic
impedances and/or capacitances that would inhibit the gate of
the MOSFET from being discharged below its threshold level
before the complementary MOSFET is turned on.
Bootstrap Component Selection
External bootstrap components, a diode and capacitor, are
required to provide sufficient gate enhancement to the upper
,
DS(ON)
MOSFET. The internal MOSFET gate driver is supplied by the
external bootstrap circuitry, as shown in Figure 7. The boot
capacitor, C
referenced to the PHASE pin. This supply is refreshed each
cycle, when D
boot diode drop, V
-
+
Just after the PWM switching cycle begins and the charge
transfer from the bootstrap capacitor to the gate capacitance
is complete, the voltage on the bootstrap capacitor is at its
lowest point during the switching cycle. The charge lost on
the bootstrap capacitor will be equal to the charge
transferred to the equivalent gate-source capacitance of the
upper MOSFET as shown in Equation 18:
×
×
×
V
t
f
IN
SW
s
(EQ. 16)
Q
GATE
2
= Io
x r
x D
DS(ON)
1
2
×
×
(
)
×
Io
r
1 D
-- - Io
=
+
(
)
DS ON
2
Where: D is the duty cycle = V
/V
,
OUT
IN
t
is the combined switch ON and OFF time, and
SW
f
is the switching frequency.
s
characteristics. The shoot-through
GS(ON)
, develops a floating supply voltage
BOOT
conducts, to a voltage of CPVOUT less the
BOOT
, plus the voltage rise across Q
D
CPVOUT
ISL6526,
ISL6526A
D
+
BOOT
V
IN
V
D
-
BOOT
C
BOOT
UGATE
Q
UPPER
PHASE
Q
LGATE
LOWER
GND
FIGURE 7. UPPER GATE DRIVE BOOTSTRAP
×
(
)
=
C
V
V
BOOT
BOOT1
BOOT2
×
×
V
t
f
IN
SW
s
(EQ. 17)
.
LOWER
NOTE:
V
= V
-V
G-S
CC
D
NOTE:
V
= V
G-S
CC
(EQ. 18)
FN9055.10
November 24, 2008