ISL8088EVAL1Z Intersil, ISL8088EVAL1Z Datasheet - Page 16

• Manufacturer Part Number: ISL8088EVAL1Z
• Description: EVAL BOARD 1 FOR ISL8088
• Manufacturer: Intersil

Specifications of ISL8088EVAL1Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

output inductor value can be increased. The inductor
ripple current can be expressed as shown in Equation 1:
ΔI
The inductor’s saturation current rating needs be at least
larger than the peak current. The ISL8088 protects the
typical peak current 1.2A. The saturation current needs
be over 1.8A for maximum output current application.
ISL8088 uses internal compensation network and the
output capacitor value is dependent on the output
voltage. The ceramic capacitor is recommended to be
X5R or X7R. The recommended minimum output
capacitor values are shown in Table 2 for the ISL8088.
In Table 2, the minimum output capacitor value is given
for different output voltage to make sure the whole
converter system is stable.
Output Voltage Selection
The output voltage of the regulator can be programmed
via an external resistor divider that is used to scale the
output voltage relative to the internal reference voltage
and feed it back to the inverting input of the error
amplifier. Refer to “Typical Application” on page 2.
TABLE 2. OUTPUT CAPACITOR VALUE vs V
=
V
-------------------------------------- -
O
•
V
L f
⎛
⎜
⎝
(V)
0.8
1.2
1.6
1.8
2.5
3.3
3.6
OUT
1
•
–
S
---------
V
V
IN
O
⎞
⎟
⎠
16
C
(µF)
6.8
8.6
OUT
10
10
10
10
10
OUT
1.0~2.2
1.0~2.2
1.0~2.2
1.5~3.3
1.5~3.3
1.5~4.7
1.5~4.7
(µH)
L
ISL8088
(EQ. 1)
ISL8088
The output voltage programming resistor, R
Channel 2), will depend on the desired output voltage of
the regulator. The value for the feedback resistor is
typically between 0Ω and 750kΩ as shown in Equation 2.
Let R
If the output voltage desired is 0.6V, then R
unpopulated and short R
performance, add 47pF in parallel to R
Input Capacitor Selection
The main functions for the input capacitor is to provide
decoupling of the parasitic inductance and to provide
filtering function to prevent the switching current flowing
back to the battery rail. One 10µF X5R or X7R ceramic
capacitor is a good starting point for the input capacitor
selection for both channels.
PCB Layout Recommendation
The PCB layout is a very important converter design step
to make sure the designed converter works well. For
ISL8088, the power loop is composed of the output
inductor (L’s), the output capacitor (C
the LX’s pins, and the GND pin. It is necessary to make
the power loop as small as possible and the connecting
traces among them should be direct, short and wide. The
switching node of the converter, the LX_ pins, and the
traces connected to the node are very noisy, so keep the
voltage feedback trace away from these noisy traces. The
input capacitor should be placed as closely as possible to
the VIN pin. The ground of input and output capacitors
should be connected as closely as possible. The heat of
the IC is mainly dissipated through the thermal pad.
Maximizing the copper area connected to the thermal
pad is preferable. In addition, a solid ground plane is
helpful for better EMI performance. It is recommended to
add at least 5 vias ground connection within the pad for
the best thermal relief.
R
2
=
3
R
3
= 100kΩ, then R
⎛
⎜
⎝
V
--------------- - 1
V
OUT
FB
–
⎞
⎟
⎠
2
2
will be:
. For faster response
OUT1
2
.
and C
2
3
(or R
is left
April 29, 2010
OUT2
(EQ. 2)
FN6858.1
5
in
)
,