FPF1039 Fairchild Semiconductor, FPF1039 Datasheet - Page 11

• Manufacturer Part Number: FPF1039
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FPF1038 / FPF1039 • Rev. 1.0.3
Application Information
Input Capacitor
This IntelliMAX™ switch doesn’t require an input
capacitor. To reduce device inrush current, a 0.1µF
ceramic capacitor, C
VIN pin. A higher value of C
voltage drop experienced as the switch is turned on into
a large capacitive load.
Output Capacitor
While this switch works without an output capacitor: if
parasitic board inductance forces V
when switching off; a 0.1µF capacitor, C
placed between V
Fall Time
Device output fall time can be calculated based on RC
constant of the external components as follows:
where t
C
The same equation works for a device with a pull-down
output resistor. R
pull-down and an external output resistor combination as:
where t
R
output capacitor.
Resistive Output Load
If resistive output load is missing, the IntelliMAX switch
without a pull-down output resistor does not discharge
the output voltage. Output voltage drop depends, in that
case, mainly on external device leaks.
Application Specifics
t
t
F
F
L
PD
is output capacitor.
=
=
=65Ω is output pull-down resistor, and C
R
R
R
L
L
L
F
F
×
×
+
is 90% to 10% fall time, R
C
is 90% to 10% fall time, R
R
R
L
PD
PD
×
Figure 37.
2
×
2 .
C
L
OUT
L
is replaced by a parallel connected
×
IN
and GND.
2
, is recommended close to the
2 .
Device Setup
IN
can be used to reduce the
L
is output load, and
OUT
L
is output load,
OUT
below GND
, should be
L
is the
(1)
(2)
At maximum operational voltage (V
inrush current might be higher than expected. Spike
current should be taken into account if V
output capacitor is much larger than the input capacitor.
Input current can be calculated as:
where switch and wire resistances are neglected and
capacitors are assumed ideal.
Estimating
formula for slew rate (dV
written as:
where supply voltage V
micro farads, and resistance is in ohms.
Example: If V
R
Maximum spike current is 1.8A, while average ramp-up
current is:
Output Discharge
FPF1039 contains a 65Ω on-chip pull-down resistor for
quick output discharge. The resistor is activated when
the switch is turned off.
Recommended Layout
For best thermal performance and minimal inductance
and parasitic effects, it is recommended to keep input
and output traces short and capacitors as close to the
device as possible. Figure 38 is a recommended layout
for this device to achieve optimum performance.
max(
I
I
max
≈
IN
IN
LOAD
Figure 38.
. 2
) t (
(
) t
75
( )
I
I
IN
=50Ω; calculate the spike current by:
≈
IN
≈
/
)
V
V
50
R
R
=
=
OUT
OUT
LOAD
LOAD
10
10
+
5
100
∗
R
5 .
(
V
) t (
50
V
) t
LOAD
OUT
IN
∗
IN
Recommended Land Pattern, Layout
+
+
. 0
+
=5.5V, C
(
(
(t)=V
(
C
0022
C
100
LOAD
LOAD
+
(
C
−
IN
=
LOAD
10
IN
/10 and
. 0
−
−
OUT
)(
is in volts, capacitances are in
C
275
C
LOAD
. 0
IN
IN
(t)/dt), spike current can be
−
05
)
A
)
C
dV
=100µF, C
dV
∗
IN
5
IN
dt
5 .
OUT
)



dt
(
. 0
) t
−
using
05
. 0
) t (
255
V
IN
IN
=5.5V), device
A )
IN
−
IN
www.fairchildsemi.com
experimental
>5V and the
. 0
=10µF, and
=
255
1
8 .
A



(3)
(4)
(6)
(5)