ISL8105BCBZ-T Intersil, ISL8105BCBZ-T Datasheet - Page 14

• Manufacturer Part Number: ISL8105BCBZ-T
• Description: IC PWM CTRLR BUCK 1PHASE 8-SOIC
• Manufacturer: Intersil

Specifications of ISL8105BCBZ-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 330kHz
• Duty Cycle: 100%
• Voltage - Supply: 6.5 V ~ 14.4 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: 8-SOIC (3.9mm Width)
• Frequency-max: 330kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

heatsink may be necessary depending upon MOSFET
power, package type, ambient temperature and air flow.
Where:
D is the duty cycle = V
t
f
When operating with a 12V power supply for V
to a minimum supply voltage of 6.5V), a wide variety of
N-Channel MOSFETs can be used. Check the absolute
maximum V
above the highest V
usually means a 20V V
with a 30V V
(around 1V or below) are not recommended for the reasons
explained in the next paragraph.
For 5V-only operation, given the reduced available gate bias
voltage (5V), logic-level transistors should be used for both
N-MOSFETs. Look for r
should be exercised with devices exhibiting very low
V
present aboard the ISL8105 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. Also avoid MOSFETs
with excessive switching times; the circuitry is expecting
transitions to occur in under 50ns or so.
Bootstrap Considerations
Figure 12 shows the top-side gate drive (BOOT pin) supplied
by a bootstrap circuit from V
C
LX pin. The supply is refreshed to a voltage of V
the boot diode drop (V
SW
S
Losses while Sinking Current
Losses while Sourcing Current
GS(ON)
BOOT
is the switching frequency.
P
P
P
P
P
is the combined switch ON and OFF time, and
TOP
TOP
BOTTOM
TOP
BOTTOM
, develops a floating supply voltage referenced to the
characteristics. The shoot-through protection
= Io
=
=
GS
Io
Io
DS
2
= Io
2
2
x r
=
rating for both MOSFETs; it needs to be
×
×
maximum rating). Low threshold transistors
Io
DS(ON)
2
r
r
DS ON
DS ON
x r
2
BIAS
×
(
(
DS(ON)
r
OUT
D
DS ON
GS
DS(ON)
) each time the lower MOSFET, Q
x D
)
)
(
voltage allowed in the system; that
×
×
rating (which typically correlates
D
D
/ V
x (1 - D)
BIAS
14
)
+
+
×
IN
1
1
-- - Io
-- - Io
2
2
ratings at 4.5V. Caution
(
,
1 D
⋅
⋅
. The boot capacitor,
–
×
×
)
V
V
+
IN
IN
1
-- - Io
2
×
×
⋅
t
t
SW
SW
×
BIAS
V
×
×
IN
BIAS
F
F
S
S
×
(or down
t
(EQ. 14)
SW
less
×
2
F
ISL8105B
,
S
turns on. Check that the voltage rating of the capacitor is
above the maximum V
rating should be sufficient for a 12V system. A value of 0.1µF
is typical for many systems driving single MOSFETs.
If V
option is to connect the BOOT pin to 12V and remove the
BOOT cap (although, you may want to add a local cap from
BOOT to GND). This will make the TGATE V
equal to (12V - 5V = 7V). That should be high enough to
drive most MOSFETs, and low enough to improve the
efficiency slightly. Do NOT leave the BOOT pin open, and try
to get the same effect by driving BOOT through V
the internal diode; this path is not designed for the high
current pulses that will result.
For low V
important, an external BOOT diode (in parallel with the
internal one) may be considered. The external diode drop
has to be lower than the internal one. The resulting higher
V
gain in efficiency should be balanced against the extra cost
and area of the external diode.
For information on the Application circuit, including a
complete Bill-of-Materials and circuit board description, can
be found in Application Note AN1288.
http://www.intersil.com/data/an/AN1288.pdf
G-S
ISL8105B
FIGURE 12. UPPER GATE DRIVE - BOOTSTRAP OPTION
BIAS
+
-
of the top-side FET will lower its r
+V
is 12V, but V
BIAS
BIAS
GND
+
-
+V
V
D
voltage applications where efficiency is very
BIAS
LX
BOOT
TGATE
BGATE
IN
BIAS
is lower (such as 5V), then another
C
voltage in the system. A 16V
+1V TO +12V
BOOT
Q
Q
1
2
DS(ON)
V
GS
NOTE:
V
G-S
G-S
. The modest
voltage
≈V
≈V
BIAS
April 15, 2010
BIAS
BIAS
FN6447.2
and
- V
D