FAN2106 Fairchild Semiconductor, FAN2106 Datasheet - Page 11

• Manufacturer Part Number: FAN2106
• Description: This part is covered in Fairchild's href="http://www
• Manufacturer: Fairchild Semiconductor

© 2009 Fairchild Semiconductor Corporation
FAN2106 • Rev. 1.1.1
MOSFET is fully enhanced. The fault latch is set
immediately upon detection.
The OV and high-side short fault protections are active
all the time, including during soft-start.
Over-Temperature Protection (OTP)
The chip incorporates an over-temperature protection
circuit that sets the fault latch when a die temperature of
about 150°C is reached. The IC restarts when the die
temperature falls below 125°C.
Auto-Restart
After a fault, EN pin is discharged by a 1µA current sink
to a 1.1V threshold before the internal 800K pull-up is
restored. A new soft-start cycle begins when EN
charges above 1.35V.
Depending on the external circuit, the FAN2106 can be
configured to remain latched-off or to automatically
restart after a fault.
Table 1. Fault / Restart Configurations
EN Pin
Pull to GND
Pull-up to V
Open
Cap. to GND
When EN is left open, restart is immediate.
If auto-restart is not desired, tie the EN pin to the VCC
pin or pull it HIGH after V
to keep the 1µA current sink from discharging EN to
1.1V. Figure 23 shows one method to pull up EN to V
for a latch configuration.
Power-Good (PGOOD) Signal
PGOOD is an open-drain output that asserts LOW when
V
Thresholds are specified in the Electrical Specifications
section. PGOOD does not assert HIGH until the fault
latch is enabled (T1.0) (see Figure 22).
OUT
Figure 23.
is out of regulation, as measured at the FB pin.
CC
with 100K
Enable Control with Latch Option
100K
Controller / Restart State
OFF (Disabled)
No Restart – Latched OFF
(After V
Immediate Restart After Fault
New Soft-Start Cycle After:
t
CC
DELAY
comes up with a logic gate
3.3n
15
14
(ms)=3.9 • C(nf)
CC
EN
VCC
Comes Up)
FAN2106
CC
11
Application Information
Bias Supply
The FAN2106 requires a 5V supply rail to bias the IC
and provide gate-drive energy. Connect a  1.0µf X5R
or X7R decoupling capacitor between VCC and PGND.
Since V
supply current is frequency and voltage dependent.
Approximate V
where frequency (f) is expressed in KHz.
Setting the Output Voltage
The output voltage of the regulator can be set from 0.8V
to 80% of V
R
current rating may need to be de-rated depending upon
the ambient temperature, power dissipated in the
package and the PCB layout.
The external resistor divider is calculated using:
Connect R
If R1 is open (see Figure 1), the output voltage is not
regulated eventually causing a latched fault after the soft
start is complete (T1.0)
If the parallel combination of R1 and R
internal SS ramp is not released and the regulator does
not start.
Setting the Switching Frequency
Switching frequency is determined by an external resistor,
R
where R
The regulator cannot start if R
Calculating the Inductor Value
Typically the inductor value is chosen based on ripple
current (IL), which is chosen between 10 to 35% of the
maximum DC load. Regulator designs that require fast
transient response use a higher ripple-current setting,
while regulator designs that require higher efficiency
keep ripple current on the low side and operate at a
lower switching frequency. The inductor value is
calculated by the following formula:
I
R
R
BIAS
T,
CC
0
BIAS
connected between the R(T) pin and AGND:
T
8 .
(
K (
mA
V

in Figure 1). For output voltages > 5V, output
)
)
CC

T


is in K and frequency (f) is in KHz.
V
. 4
BIAS
(
is used to drive the internal MOSFET gates,
10
OUT
58
IN
6
CC
between FB and AGND.
R
by an external resistor divider (R1 and
/


65
1
) f
current (I
0
[(
8 .

V
135
V
CC
227


650
5
CC

) can be calculated using:
nA
T
. 0
is left open.
013
)

BIAS
f (

is  1K, the
128
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)]
(1)
(2)
(3)