ISL6527AEVAL2 Intersil, ISL6527AEVAL2 Datasheet - Page 13

• Manufacturer Part Number: ISL6527AEVAL2
• Description: EVALUATION BOARD QFN ISL6527A
• Manufacturer: Intersil

Specifications of ISL6527AEVAL2

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 0.75 ~ 3V
• Current - Output: 5A
• Voltage - Input: 3.3 ~ 5V
• Regulator Topology: Buck
• Frequency - Switching: 600kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ISL6527A
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

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 19:
where Q
MOSFET, C
the bootstrap voltage immediately before turn-on, and
V
The bootstrap capacitor begins its refresh cycle when the gate
drive begins to turn-off the upper MOSFET. A refresh cycle
ends when the upper MOSFET is turned on again, which varies
depending on the switching frequency and duty cycle.
Q
BOOT2
GATE
+
-
ISL6527A
ISL6527,
FIGURE 7. UPPER GATE DRIVE BOOTSTRAP
=
GATE
is the bootstrap voltage immediately after turn-on.
C
BOOT
BOOT
is the maximum total gate charge of the upper
GND
×
is the bootstrap capacitance, V
UGATE
PHASE
(
CPVOUT
BOOT
LGATE
DBOOT
V
BOOT1
CBOOT
+
-
V
13
–
D
V
BOOT2
Q
Q
VIN
UPPER
LOWER
)
NOTE:
V
NOTE:
V
G-S
G-S
≈ V
BOOT1
≈ V
ISL6527, ISL6527A
CC
CC
(EQ. 19)
-V
is
D
The minimum bootstrap capacitance can be calculated by
rearranging Equation 19 and solving for CBOOT in
Equation 20.
Typical gate charge values for MOSFETs considered in
these types of applications range from 20 to 100nC. Since
the voltage drop across Q
simply V
minimize the voltage drop across the bootstrap capacitor
during the on-time of the upper MOSFET. Initial calculations
with V
bootstrap capacitor range.
For example, consider an upper MOSFET is chosen with a
maximum gate charge, Q
drop across the bootstrap capacitor to 1V results in a value
of no less than 0.1µF. The tolerance of the ceramic capacitor
should also be considered when selecting the final bootstrap
capacitance value.
A fast recovery diode is recommended when selecting a
bootstrap diode to reduce the impact of reverse recovery
charge loss. Otherwise, the recovery charge, Q
have to be added to the gate charge of the MOSFET and
taken into consideration when calculating the minimum
bootstrap capacitance.
ISL6527, ISL6527A DC/DC Converter
Application Circuit
Figure 8 shows an application circuit of a DC/DC Converter.
Detailed information on the circuit, including a complete
Bill-of-Materials and circuit board description, can be found
in Application Note AN1021.
http://www.intersil.com/data/an/an1021.pdf
C
BOOT
BOOT2
≥
CPVOUT
---------------------------------------------------- -
V
BOOT1
no less than 4V will quickly help narrow the
Q
GATE
- V
–
V
D
BOOT2
. A schottky diode is recommended to
g
LOWER
, of 100nC. Limiting the voltage
is negligible, V
November 18, 2008
RR
BOOT1
, would
(EQ. 20)
FN9056.10
is