FPF2700MX [FAIRCHILD]
Adjustable Over-Current Protection Load Switches; 可调式过电流保护负载开关
| 型号： | FPF2700MX |
| 厂家： | 
FAIRCHILD SEMICONDUCTOR |
| 描述： | Adjustable Over-Current Protection Load Switches |
| 文件： | 总19页 (文件大小：1103K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
January 2011
FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A
Adjustable Over-Current Protection Load Switches
Features
Description
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2.8V to 36V Input Voltage Range
The AccuPower™ FPF270X series is a family of
current-limit load switches that provide full protection to
systems and loads from excess current conditions.
Minimum current limit is adjustable from 0.4A to 2.0A.
The FPF270X contains a slew-rate-controlled N-channel
MOSFET and slew-rated turn-on to prevent power bus
disturbances from being caused by “hot plugging” loads
or momentary excess load demands. The input voltage
range is 2.8V to 36V. Loads can be activated or
deactivated with a low-voltage logic-compatible ON pin.
Fault conditions can be monitored using the error flag
pin and/or the power-good pin.
Typical RDS(ON)=88m
0.4A to 2A Adjustable Current Limit (Min.)
Slew Rate Controlled
ESD Protected, above 2000V HBM
Thermal Shutdown
Active LOW Enable
UVLO Protection
Power-Good Output
Applications
Each member of the FPF270X family serves a category
of load-fault response. All devices clamp the load
current so that it cannot exceed an externally
programmed current level. An over temperature feature
provides further device protection in case of excessive
levels of power dissipation.
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Motor Drives
Digital Cameras
Consumer Electronics
Industrial
FPF2700 responds to an overload condition that lasts
longer than a fixed blanking period by turning off the
load, followed by a retry after the auto-restart time.
Computing
Hard Disk Drives
Telecom Equipment
FPF2701 responds to an overload condition that lasts
longer than a fixed blanking period by latching off the
load. The load remains off unless either the ON pin is
toggled or the input voltage cycles through UVLO.
FPF2702 is intended to be used with external fault
management. Like the FPF2700 and FPF2701, it sets
the fault signal pin LOW when it activates current
clamping. This device is intended for applications where
external fault management coordinates the overload
response with the FPF2702.
Figure 1. MLP (Top View) Figure 2. MLP (Bottom View)
The FPF270X is available in a space-saving Pb and
Halogen free, 8-lead MLP 3x3mm and SO8 packages.
Figure 3. SO8 (Top View)
Ordering Information
Part
Number
Current Limit
Blanking Time [ms]
Auto-Restart
Time [ms]
ON Pin
Activity
Current Limit [A]
Package
FPF2700MPX
FPF2701MPX
FPF2702MPX
FPF2700MX
FPF2701MX
FPF2702MX
0.4 – 2.0
0.4 – 2.0
0.4 – 2.0
0.4 – 2.0
0.4 – 2.0
0.4 – 2.0
0.5
0.5
NA
0.5
0.5
NA
127.5
NA
Active LOW
Active LOW
Active LOW
Active LOW
Active LOW
Active LOW
MLP3X3
MLP3X3
MLP3X3
SO8
NA
127.5
NA
SO8
NA
SO8
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
Application Diagram
36V MAX.
TO LOAD
VIN
ON
VOUT
FLAGB
PGOOD
OFF
ON
COUT
VIN
2.8V – 36V
CIN
ISET
RSET
GND
Figure 4. Typical Application
Block Diagram
Figure 5. Block Diagram
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
2
Pin Configurations
1
2
3
VIN
VOUT
8
7
VOUT
8
1
2
VIN
PGOOD
FLAGB
FLAGB
7
PGOOD
GND
6
5
NC
ISET
ON
3
4
ISET
ON
NC
6
5
GND
4
GND
Figure 6. MLP (Bottom View)
Figure 7. SO8 (Top View)
Pin Definitions
Pin #
Name
Description
1
VIN
Supply Input. Input to the power switch and the supply voltage for the IC.
Power-Good Output. Open-drain output to indicate that output voltage has reached 90% of
input voltage.
2
PGOOD
3
4
5
6
ISET
ON
Current Limit Set Input. A resistor from ISET to ground sets the current limit for the switch.
ON Control Input. Active LOW.
Ground
GND
NC
No connection. Leave open or connect to ground.
Fault Output. Active LOW, open-drain output that indicates current limit, under-voltage, or
over -temperature state.
7
8
FLAGB
VOUT
Switch Output. Output of the power switch.
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
3
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device
reliability. The absolute maximum ratings are stress ratings only.
Symbol
Parameter
Min.
-0.3
-0.3
-0.3
Max.
40
Unit
V
PGOOD, FLAGB, VIN to GND
VOUT to GND
ON to GND
VIN + 0.3
6
V
V
MLP 3x3(1), See Figure 8
SO8(1), See Figure 10
1.25
1.00
3.5
PD
Power Dissipation (TA=25°C)
W
ISW
TJ
Maximum Continuous Switch Current
Operating Junction Temperature
Storage Temperature
A
-40
-65
+125
+150
°C
°C
TSTG
Human Body Model, JESD22-A114
2000
2000
Electrostatic Discharge
Protection Level
ESD
V
Charged Device Model, JESD22-C101
MLP 3x3(1), See Figure 8
SO8(1), See Figure 10
80
Thermal Resistance,
Junction to Ambient
°C/W
JA
102
Note:
1. Thermal resistance, θJA, is determined with the device mounted on a one inch square pad, 2oz copper pad, and
a 1.5 x 1.5in. board of FR-4 material.
Figure 8. 80°C/W Mounted on a 1in2 Pad of
2oz. Copper
Figure 9. 226°C/W Mounted on a Minimum Pad of
2oz. Copper
Figure 10. 102°C/W mounted on a 1in2 Pad of
2oz. Copper
Figure 11. 181°C/W Mounted on a Minimum Pad of
2oz. Copper
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to Absolute Maximum Ratings.
Symbol
VIN
Parameter
Min.
2.8
Max.
36.0
85
Unit
V
Input Supply Voltage
Ambient Operating Temperature
TA
-40
°C
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
4
Electrical Characteristics
VIN=2.8 to 36V and TA=-40 to +85°C unless otherwise noted. Typical values are at VIN=12V and TA=25°C.
Symbol
Parameter
Conditions
Min. Typ. Max. Unit
Basic Operation
VIN
IQ
Operating Voltage
Quiescent Current
2.8
36.0
140
14
V
VIN=12V, VON=0V, IOUT=0A
VIN=36V, VON=3.3V, IOUT=0A
TA=25°C, VIN=12V
92
5
μA
μA
ISHDN
Shutdown Current
88
114
140
114
140
TA=-40 to +85°C, VIN=12V
TA=25°C, VIN=5V
RON
On-Resistance
mΩ
88
TA=-40 to +85°C, VIN=5V
VIN=2.8 to 36V
VIH
VIL
ON Input Logic HIGH Voltage
ON Input Logic LOW Voltage
ON Input Leakage
2.0
-1
V
V
VIN=2.8 to 36V
0.8
1
ILK
VON=5.5V or GND
μA
μA
V
ISWOFF
Off Switch Leakage
VIN=36V, VON=3.3V, VOUT=0V
VIN=5V, ISINK=1mA
0.01
0.1
VFLAGB(LO) FLAGB Output Logic LOW Voltage
0.2
1
FLAGB Output Logic HIGH Leakage
IFLAGB(HI)
Current
VIN=36V, Switch On, VFLAGB=36V
μA
VIN=5V, VOUT as Percent of VIN,
VPGOOD
PGOOD Trip Voltage
90
%
VOUT Rising
VIN=5V, VOUT as Percent of VIN,
VPGOOD(HYS) PGOOD Hysteresis
VPGOOD(LO) PGOOD Output Logic LOW Voltage
IPGOOD(HI) PGOOD Output High Leakage Current
Protections
3
%
V
VOUT Falling
VIN=5V, ISINK=1mA
0.1
0.2
1
VIN=36V, Switch ON,
μA
VPGOOD=36V
0.8 x 1.0 x 1.2 x
ILIM
ISC
Current Limit
TA=25°C
A
A
INOM
INOM
INOM
VOUT < 2V, Switch in Over-
Current Condition
0.75 x
INOM
Short Circuit Current Limit
Shutdown Threshold
Return from Shutdown
Hysteresis
140
110
30
TSD
Thermal Shutdown
°C
UVLO
Under-Voltage Shutdown
VIN Increasing
2.3
2.5
100
2.7
V
UVLO_HYST Under-Voltage Shutdown Hysteresis
mV
Dynamic
tdon
tdoff
Turn On Delay
2.7
0.1
Turn Off Delay
RL=500Ω, CL=2uF
ms
tR
VOUT Rise Time
7.5
tF
VOUT Fall Time
1.5
tBLANK
tRESTART
tCLR
Over-Current Blanking Time
Auto-Restart Time
Current-Limit Response Time
FPF2700/1, TA=25°C
FPF2700, TA=25°C
VIN=12V, VON=0V
0.25
0.50
0.75
ms
ms
μs
63.8 127.5 191.2
50
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
5
Timing Diagram
90
90
10
10
VOUT
VON
tR
tF
3.3
50
50
90
10
VOUT
tdon
tdoff
tON = tR + tdon tOFF = tF + tdoff
Figure 12. Timing Diagram
Typical Performance Characteristics
VIN = 12V and TA = 25°C.
TA = 25°C
VIN = 12V
VIH
VIH
VIL
VIL
Figure 13. ON Threshold vs. Supply
Figure 14. ON Threshold vs. Temperature
VON = 0V
TA = 125°C
VON = 5V
TA = 125°C
TA = 85°C
TA = 25°C
TA = 85°C
TA = 25°C
TA = ‐40°C
TA = ‐40°C
Figure 15. Quiescent Current vs. Supply Voltage (ON) Figure 16. Quiescent Current vs. Supply Voltage (OFF)
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
6
Typical Performance Characteristics
VIN = 12V and TA = 25°C.
Figure 17. On Resistance vs. Supply Voltage
Figure 18. On Resistance vs. Junction Temperature
VIN = 12V
RL = 500
CL = 2µF
Figure 19. Turn-On Delay vs. Junction Temperature Figure 20. Output Rise Time vs. Junction Temperature
Figure 21. Turn-Off Delay vs. Junction Temperature Figure 22. Output Fall Time vs. Junction Temperature
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
7
Typical Operation Characteristics of FPF2700 and FPF2701
When VOUT<2V, the current limit is set to 75% of ILIM
.
Figure 23. Normal Startup to 0.5X ILIM
Figure 24. OUT Shorted to GND, Short Condition
Persists (SOA Protection Followed by Current-Limited
Operation)
Figure 25. OUT Overloaded with 1.5X ILIM
(Long-Duration Overload)
Figure 26. OUT Shorted to GND, Short Condition
Removed (SOA Protection Followed by
Normal Operation)
Figure 27. OUT Overloaded with 1.5X ILIM
(Transient Overload)
© 2010 Fairchild Semiconductor Corporation
www.fairchildsemi.com
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
8
Typical Operation Characteristics of FPF2702
Figure 28. OUT Shorted to GND, Short Condition Persists
(SOA Protection Current Limit Followed by Current Limit)
Figure 29. OUT Overloaded with 1.5X ILIM (Long-Duration Overload)
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
9
Typical Performance Characteristics FPF270X
VIN = 12V and TA = 25°C.
Figure 30. 12V Turn-On Delay (RL=500, COUT=2µF)
Figure 31. 12V Turn-Off Delay (RL=500, COUT=2µF)
Figure 32. 12V Blanking Time
(Output Overloaded and tblank Expired, FPF2700/01,
Figure 33. 12V Restart Time
(Switch Turned ON into Persistent Over-Current
Condition,tRESTART~127.5ms)
(2)
I
LIM=1A, ILOAD=3.3A, COUT=µF, RLOAD=500) VOC
Figure 34. Soft Overload and Constant Current
(ILOAD > ILIM, FPF2702 Enters Constant Current Mode,
Figure 35. OUT Shorted to GND, Short Condition
Removed (SOA Protection Followed by a Normal
Operation, FPF2700 / FPF2701)
Running at ILIM
)
Note:
2. VOC signal forces the device into an over-current condition by loading a 500m resistor to the output through an
NMOS. VOC is the gate drive of the NMOS.
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
10
Application Information
Description of Operation
Current Limiting
The FPF270X family of current limit load switches is
designed to meet the power requirements of a variety of
applications with wide input voltage range of 2.8V to 36V
and adjustable current-limit value. The FPF270X family
offers control and protection while providing optimum
operation current for safe design practices. The core of
each switch is a typical 88mΩ (VIN = 12V) N-channel
MOSFET and a controller capable of functioning over an
input voltage range of 2.8V to 36V.
The current limit ensures that the current through the
switch doesn't exceed a maximum value while not
limiting at less than a minimum value. The current-limit
level is adjustable through an external resistor
connected between the ISET pin and GND.
The typical current limit level is adjustable from 500mA
to 2.5A. The minimum current limit (ILIM(MIN)) range is
from 0.4A to 2.0A, including 20% current-limit tolerance.
The FPF2700 and FPF2701 have a blanking time during
which the switch acts as a constant-current source
(Figure 27). If the over-current condition persists beyond
the blanking time, the FPF2700 latches off and shuts the
switch off (Figure 32). If the ON pin is kept active, an
auto-restart feature releases the switch and turns the
switch on again after the auto-restart time (Figure 33). If
the over-current condition persists beyond the blanking
time, the FPF2701 latch-off feature shuts the switch off.
The switch is kept off until the ON pin is toggled or input
power is cycled. The FPF2702 has no current-limit
blanking period, so it remains in a constant-current state
until the ON pin is deactivated or the thermal shutdown
turns off the switch.
FPF270X offers adjustable current limiting, under-
voltage lockout (UVLO), power-good indicator
(PGOOD), fault flag output (FLAGB), and thermal
shutdown protection. In the event of an over-current
condition, the load switch limits the load to the current
limit value. The current limit value for each switch can
be adjusted from 400mA to 2A through the ISET pin.
On/Off Control
The ON pin is active LOW for and controls the state of
the switch. Pulling the ON pin continuously to LOW
holds the switch in ON state. The switch moves into
OFF state when the ON pin is pulled HIGH. The ON pin
can be pulled HIGH to a maximum voltage of 5.5V.
Besides the current-limiting functionality, the switch is
protected by the thermal shutdown protection and an
independent SOA protection circuit is available.
An under-voltage condition on the input voltage or a
junction temperature in excess of 140°C overrides the
ON control and turns off the switch. In addition, an over-
current condition causes the switch to turn off in the
FPF2700 and FPF2701 after the expiration of the
blanking time. The FPF2700 has an auto-restart feature
that automatically turns the switch ON again after the
auto-restart time. For the FPF2701, the ON pin must be
toggled to turn the switch on again. The FPF2702 does
not turn off in response to an over-current condition; it
remains operating in Constant-Current Mode as long as
ON is enabled and the thermal shutdown or UVLO have
not activated. The ON pin does not have internal pull-
down or pull-up resistors and should not be left floating.
SOA Protection Current Limit (IOUT > 12A)
FPF270X has an SOA protection feature to protect the
load switch in response to current surges exceeding 12A
in normal operation. If a short-circuit event occurs
(IOUT>12A), the switch is turned off in about 1µs by an
independent Safe Operating Area (SOA) protection
circuit (Figure 26, Figure 28). This feature protects the
switch in case of sudden, high-current events at the
output, such as a short to GND. The switch turns on
automatically after a turn-on delay of about 2.7ms.
Short-Circuit Current Limit (VOUT < VSCTH = 2V)
Fault Reporting
When the output voltage drops below the short-circuit
threshold voltage, VSCTH, the current-limit value re-
conditions itself to the short-circuit current limit value,
Upon detection of an over-current condition, an input
UVLO, or an over-temperature condition, the FLAGB
signals the Fault Mode by activating LOW. In the event
of an over-current condition for the FPF2700 or
FPF2701, the FLAGB goes LOW at the end of the
blanking time (Figure 24 and Figure 25). FLAGB goes
LOW immediately for the FPF2702 (Figure 29). If the
over-current condition lasts longer than blanking time,
FLAGB remains LOW through the auto-restart time for
the FPF2700. For the FPF2701, FLAGB is latched LOW
and ON must be toggled to release it.
which is 75% of the nominal current limit (0.75 x ILIM,
)
(Figure 24). This prevents early thermal shutdown by
reducing the power dissipation of the device. The VSCTH
value is set at 2V. At about VOUT = 2.1V, the switch is
removed from short-circuit current-limiting mode and the
current limit is set to the nominal current limit value.
Setting the Current Limit Value
For FPF2702, FLAGB is LOW during a fault and
immediately returns HIGH at the end of the fault
condition. FLAGB is an open-drain MOSFET that
requires a pull-up resistor. The maximum pull-up voltage
is 36V (Figure 29).
The FPF270X has an adjustable 0.4A to 2.0A minimum
current limit set through an external resistor, RSET
,
connected between ISET and GND. A precision RSET
value must be used, such as 1% tolerance or lower, to
minimize the total current limit tolerance of the system.
During shutdown, the pull-down on FLAGB is disabled to
reduce current draw from the supply. A 100KΩ pull-up
resistor is recommended in the application.
Use the following equation to calculate the value of the
resistor for intended typical current limit value:
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
11
277.5
RSET (K)
Power Good
(1)
ILIM(TYP)(A)
FPF270X has a power good feature. The PGOOD pin is
an open-drain MOSFET that asserts HIGH when the
output voltage reaches 90% of the input voltage (Figure
26). A typical 3% PGOOD hysteresis is added to
PGOOD to prevent PGOOD from chattering as VOUT
falls near the PGOOD threshold voltage.
ILIM(TYP) is the typical current limit value based on a given
RSET
.
Table 1. RSET Selection Guide
Current Limit [A]
RSET
(k)
Tol. (%)
The PGOOD pin requires an external pull-up resistor
connected to an external voltage source compatible with
input levels of other chips connected to this pin. PGOOD
is kept LOW when the device is inactive. To save
current in the OFF state, the pull-up resistor of the
PGOOD pin can be connected to the output voltage
when there is no battery, provided that compatibility with
the input levels of other devices connected to PGOOD is
observed. A typical value of 100kΩ is recommended for
the pull up resistor. When the power-good feature is not
used in the application, the PGOOD pin can be
connected to GND.
Min.
Typ.
2.50
2.24
1.89
1.52
1.26
1.01
0.74
0.51
Max.
111
124
147
182
220
274
374
549
2.00
1.79
1.51
1.22
1.01
0.81
0.59
0.40
3.00
2.69
2.27
1.83
1.51
1.22
0.89
0.61
20
20
20
20
20
20
20
20
Thermal Shutdown
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
100
Thermal shutdown protects the die from internally or
externally generated excessive temperatures. During an
over-temperature condition; as the temperature
increases above 140°C, FLAGB is activated and the
switch is turned off.
When the die cools down sufficiently (die temperature
drops below the threshold level), the switch
automatically turns on again. To avoid unwanted thermal
oscillations, a 30°C (typical) thermal hysteresis is
implemented between thermal shutdown entry and exit
temperatures. Proper board layout is required to prevent
premature thermal shutdown (see Figure 38 for thermal
shutdown behavior on FPF2702).
200
300
400
500
600
R
SET (k)
Figure 36. ILIM vs. RSET
Under-Voltage Lockout (UVLO)
The under-voltage lockout feature turns off the switch if
the input voltage drops below the under-voltage lockout
threshold. With the ON pin active (ON pin pulled LOW),
the input voltage rising above the under-voltage lockout
threshold causes a controlled turn-on of the switch
(Figure 37). The UVLO threshold voltage is set internally
at 2.5V for VIN rising. The under-voltage lockout
threshold has a 0.1V hysteresis.
Figure 38. FPF2702 Thermal Shutdown Behavior
Figure 37. Under-Voltage Lockout Performance
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
12
SOA (FPF2702)
During extended output-short conditions, excessive
power dissipation occurs in the load switch. FPF2700
and PFP2701 are protected by turning off the load
switch after blanking time. FPF2702 has no blanking
time feature; please refer to Note 3.
It is possible to estimate the SOA for the two FPF2702
packages, MPX and MX, through their respective SOA
curves shown in Figure 39 and Figure 40. These curves
provide a reference on how long the load switch
survives under the worst-case scenario with minimum
pad size of one square inch.(1)
Figure 39. FPF2702 MPX SOA
Figure 40. FPF2702 MX SOA
Note:
3. To protect FPF2702 from an extended short condition, additional protection must be implemented in the system
to protect the device. For example, the FLAGB and PGOOD signal can be used to monitor the short-circuit fault
condition. In applications where FPF2702 can be exposed to persistent short-circuit conditions, it should be used
only with external fault management control to protect the switch.
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
13
Input Capacitor
Power Dissipation
To limit the voltage drop on the input supply caused by
transient inrush currents when the switch is turned on
into a discharged load capacitor or short-circuit; an input
capacitor, CIN, is recommended between the IN and
GND pins. The FPF270X features a fast current limit
response time (50μs). During this period, the device
relies on the input capacitor to supply the load current. A
10μF to 100μF ceramic capacitor is adequate for CIN in
most cases. Larger CIN values may be required in high-
voltage or high-current applications. An electrolytic
capacitor can be used in parallel to further reduce the
voltage drop.
During normal operation as a switch, the power
dissipation of the device is small and has little effect on
the operating temperature of the part. The maximum
power dissipation for the switch in normal operation
occurs just before the switch enters into current limit.
This may be calculated using the equation:
2
PD _ MAX ( NormalOper ation ) (ILIM ( Max )
)
RON ( MAX )
(3)
The maximum junction temperature should be limited to
125°C under normal operation. Junction temperature
can be calculated using the equation:
TJ PD JA TA
(4)
Output Capacitor
where:
A 0.1μF to 1μF capacitor, COUT, should be placed
between the OUT and GND pins. This capacitor helps
prevent parasitic board inductances from forcing the
output voltage below ground when the switch turns
off. This capacitor should have a low dissipation
factor. An X7R Multilayer Ceramic Chip (MLCC)
capacitor is recommended.
.
.
.
TJ is junction temperature;
PD is power dissipation on the switch;
Θ
JA is the thermal resistance, junction-to-ambient of
the package; and
.
TA is ambient temperature.
During startup, the total output current consists of both
the load current and the charge current of the output
capacitor. For the FPF2700 and FPF2701; if the total
output current exceeds the set current limit threshold
(determined via RSET) for longer than the blanking time,
the device may not be able to start properly. This
imposes an upper limit to the value of the output
capacitor, given the load current and the selected
current limit value. COUT should not exceed the COUTmax
calculated in Equation 2 or the switch does not start
properly due to the set current limit:
Design Example
For a 12V application and ILIM
power dissipation in a normal operation is calculated as:
= 1A, maximum
(Max)
PD _MAX(NormalOperation)(VIN12V ) (1)2 0.140 140mW
(5)
FPF2702 PD(Max) during OC:
If device is in over-current condition and VOUT>2V,
power dissipation can be calculated as:
PD = (VIN - VOUT) x ILIM (Max)
(6)
COUT max ILIM _MIN 500s /V
(2)
If device is in short-circuit current limit and VOUT < 2V,
power dissipation can be calculated as:
High-Voltage Operation (Output Capacitor)
During a hard short condition on the output while
operating at greater than 24V VIN, a large instantaneous
inrush current is delivered to the shorted output. A
capacitor must be placed at the OUTPUT pin, acting as
a current source to support the instantaneous current
draw (Table 2). A low-ESR capacitor is recommended.
Once the value of the output capacitor is determined
from Table 2, Equation 2 must be reevaluated.
PD = (VIN - VOUT) x (0.75 x ILIM (Max)
)
(7)
Design Example:
Using FPF2702 in a VIN = 5V application where ILIM (Max)
= 2A, assuming VOUT = 2.5V; power dissipation across
the switch is calculated as:
PD = (5 - 2.5) x 2 = 5W
(8)
Table 2. COUT Selection Guide
Whereas in a short-circuit current-limit condition (VOUT
0V), power dissipation is calculated as:
≈
VIN (V)
Capacitance (μF)
24< VIN ≤ 27
27< VIN ≤ 32
32< VIN ≤ 36
22
47
68
PD = ((VIN - VOUT) x (0.75 x ILIM (Max)) = (5 - 0) x
(0.75 x 2) = 7.5W
(9)
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
14
PCB Layout Recommendations
For the best performance, all traces should be as short
as possible. To be most effective, the input and output
capacitors should be placed close to the device to
minimize the effects that parasitic trace inductances
may have on normal and short-circuit operation (Figure
42). Using wide traces for IN, OUT, and GND pins helps
minimize parasitic electrical effects as well as the case-
to-ambient thermal impedance.
3. The IN, OUT, and GND pins dissipate most of the
heat generated during high-load current condition.
The layout suggested in Figure 42 and Figure 43 is
strongly recommended illustrating a proper layout
for devices in MLP 3x3 packages. IN, OUT, and
GND pins are connected to adequate copper so
that heat may be transferred as efficiently as
possible out of the device. The low-power FLAGB
and ON pins traces may be laid-out diagonally from
the device to maximize the area available to the
ground pad. Place the input and output capacitors
as close as possible to the device.
To minimize the interference between analog ground
(chip ground, pin 5) and power ground during load
current excursion, the ground terminal of the input and
output capacitors and the RSET resistor should be routed
directly to chip ground and away from power ground.
Improving Thermal Performance
Improper layout could result in higher junction
temperature and trigger thermal shutdown protection.
This is particularly significant for the FPF2702, where
the device operates in Constant Current Mode under
overload conditions. During fault conditions, the power
dissipation of the switch could exceed the maximum
absolute power dissipation.
The following techniques improve the thermal
performance of this family of devices. These techniques
are listed in order of the significance of their impact.
Figure 42. Proper Layout of Output and Ground
Copper Area (Top, SST, and AST Layers)
1. Thermal performance of the load switch can be
improved by connecting the Die Attach Pad (DAP) of
the MLP 3x3 package to the GND plane of the PCB.
2. Embedding two exposed through-hole vias into the
DAP provides a path for heat to transfer to the back
GND plane of the PCB. A drill size of round, 15 mils
(0.4mm)
with
1-ounce
copper
plating
is
A
recommended for appropriate solder reflow.
smaller-size hole prevents the solder from
penetrating into the via, resulting in device lift-up.
Similarly, a larger hole consumes excessive solder
and may result in voiding the DAP.
Figure 43. Proper Layout (Bottom and ASB Layers)
Figure 41. Two Through-Hole Open Vias Embedded
in the DAP
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
15
FPF270x Demonstration Board
The FPF270X demonstration board has components
and circuitry to demonstrate the load switch’s functions
and features. Thermal performance of the board is
improved using the techniques recommended in the
layout recommendations section. Additional information
about demonstration board can be found in the
FPF270X board users guide.
Figure 44. Top, SST, and AST Layers
Figure 45. Bottom and ASB Layers
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
16
Physical Dimensions
5.00
4.80
A
0.65
3.81
8
5
B
1.75
6.20
5.80
4.00
3.80
5.60
1
4
PIN ONE
INDICATOR
1.27
1.27
(0.33)
M
0.25
C B A
LAND PATTERN RECOMMENDATION
SEE DETAIL A
0.25
0.10
0.25
0.19
C
1.75 MAX
0.10
C
0.51
0.33
OPTION A - BEVEL EDGE
0.50
0.25
x 45°
R0.10
R0.10
GAGE PLANE
OPTION B - NO BEVEL EDGE
0.36
NOTES: UNLESS OTHERWISE SPECIFIED
8°
0°
0.90
A) THIS PACKAGE CONFORMS TO JEDEC
MS-012, VARIATION AA, ISSUE C,
B) ALL DIMENSIONS ARE IN MILLIMETERS.
C) DIMENSIONS DO NOT INCLUDE MOLD
FLASH OR BURRS.
SEATING PLANE
(1.04)
0.406
D) LANDPATTERN STANDARD: SOIC127P600X175-8M.
E) DRAWING FILENAME: M08AREV13
DETAIL A
SCALE: 2:1
Figure 46. 8-Lead, Small Outline Package (SOP)
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner
without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or
obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the
warranty therein, which covers Fairchild products.
Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings:
http://www.fairchildsemi.com/packaging/.
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
17
Physical Dimensions
0.15 C
2X
3.00
A
2.52
B
5
8
1.94
3.00
1.70
3.30
PIN1
IDENT
0.56 8X
0.15 C
1
4
TOP VIEW
2X
0.47 8X
0.65
RECOMMENDED LAND PATTERN
0.80 MAX
0.10 C
(0.20)
0.08 C
0.05
0.00
NOTES:
C
SIDE VIEW
A. PACKAGE CONFORMS TO JEDEC MO-229
EXCEPT WHERE NOTED.
SEATING
PLANE
B. DIMENSIONS ARE IN MILLIMETERS.
C. DIMENSIONS AND TOLERANCES PER
ASME Y14.5M, 1994.
D. LAND PATTERN RECOMMENDATION IS
BASED ON FSC DESIGN ONLY.
2.45
2.35
(0.35) 4X
PIN 1
IDENT
E. DRAWING FILENAME: MKT-MLP08Vrev1.
1
4
1.75
1.65
0.40
8X
0.30
0.10
0.05
C A B
C
8
5
0.40
0.30
0.65
8X
BOTTOM VIEW
Figure 1.
8-Lead, 3x3mm Molded Leadless Package (MLP)
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner
without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or
obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the
warranty therein, which covers Fairchild products.
Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings:
http://www.fairchildsemi.com/packaging/.
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
18
© 2010 Fairchild Semiconductor Corporation
FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2
www.fairchildsemi.com
19
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