ISL8118IRZ Intersil, ISL8118IRZ Datasheet - Page 15

• Manufacturer Part Number: ISL8118IRZ
• Description: IC CTRLR PWM 1-PHASE 28-QFN
• Manufacturer: Intersil

Specifications of ISL8118IRZ

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 2MHz
• Duty Cycle: 100%
• Voltage - Supply: 2.97 V ~ 22 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-VQFN Exposed Pad, 28-HVQFN, 28-SQFN, 28-DHVQFN
• Frequency-max: 2MHz
• Rohs Compliant: YES
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

As the VDIFF pin is connected internally to the
OV/UV/PGOOD comparator, an external resistor divider
must then be connected to VDIFF to provide correct voltage
information for the OV/UV comparator. An RC filter should
be used if VDIFF is to be connected directly to FB instead of
to VOUT through a separate resistor divider network. This
filter prevents noise injection from disturbing the
OV/UV/PGOOD comparators on VDIFF. VDIFF may also be
connected to the SS pin, which completely bypasses the
OV/UV/PGOOD functionality.
Application Guidelines
Layout Considerations
As in any high frequency switching converter, layout is very
important. Switching current from one power device to
another can generate voltage transients across the
impedances of the interconnecting bond wires and circuit
traces. These interconnecting impedances should be
minimized by using wide, short printed circuit traces. The
critical components should be located as close together as
possible using ground plane construction or single point
grounding.
Figure 7 shows the critical power components of the
converter. To minimize the voltage overshoot/undershoot the
interconnecting wires indicated by heavy lines should be part
of ground or power plane in a printed circuit board. The
components shown in Figure 8 should be located as close
together as possible. Please note that the capacitors CIN
and CO each represent numerous physical capacitors.
Locate the ISL8118 within 3 inches of the MOSFETs, Q1 and
Q2. The circuit traces for the MOSFETs’ gate and source
connections from the ISL8118 must be sized to handle up to
4A peak current.
VOUT (LOCAL)
GND (LOCAL)
FIGURE 6. SIMPLIFIED UNITY GAIN DIFFERENITAL SENSING IMPLEMENTATION
15
800mV
VCC
10Ω
10Ω
(REMOTE)
VSENSE-
VSENSN
R
C
OS
SEN
(REMOTE)
VSENSE+
VSENSP
ISL8118
R
GAIN = 1
FB
V
SS
Proper grounding of the IC is important for correct operation in
noisy environments. The PGND pin should be connected to
board ground at the source of the bottom side MOSFET with a
wide short trace. The GND pin should be connected to a large
copper fill under the IC which is subsequently connected to
board ground at a quite location on the board, typically found
at an input or output bulk (electrolytic) capacitor.
VDIFF
ISL8118
FIGURE 7. PRINTED CIRCUIT BOARD POWER AND
FIGURE 8. PRINTED CIRCUIT BOARD SMALL SIGNAL
C
SS
SS
Z
OV/UV
COMP
IN
GND
BGATE
TGATE
ISL8118
PGND
GROUND PLANES OR ISLANDS
LAYOUT GUIDELINES
LX
ERROR AMP
FB
PGND
Z
FB
LX
C
PVCC
BOOT
BOOT
+5V
V
Q2
Q1
RETURN
COMP
IN
C
PVCC
D1
C
Q1
+V
Q2
IN
IN
L
L
O
O
C
C
O
O
V
OUT
April 7, 2009
V
FN6325.1
OUT