BL2555
Load Switch with Adjustable Current Limit
DESCRIPTION
The BL2555 is a load switch which provides full
protection to systems and loads which may
encounter large current conditions.
BL2555 offers a 95mΩ current-limited switch which
can operate over an input voltage range of 2.5-5.5V.
The current limit can be externally programmed by
a precision resistor, ranges from 75mA to 1.7A.
Switch control is by a logic input (EN) capable of
interfacing directly with low voltage control signals.
Current is prevented from flowing when the switch
is off and the output voltage is higher than the input
voltage.
BL2555 also features thermal shutdown protection
which shuts off the switch to prevent damage to the
part when a continuous over-current condition
causes excessive heating. When the switch current
reaches the current limit, the parts operate in a
constant-current mode to prohibit excessive
currents from causing damage.
BL2555 is in a tiny DFN2x2-6L package
FEATURES
Up to 1.5A Max Load current
Accurate Current-limit threshold: +/-5%
Programmable Current-limit : 75mA to 1.7A
Fast Over-Current Response
Reversed Current blocking
Thermal Shutdown, UVLO protection
Tiny DFN2x2-6L Package
APPLICATIONS
USB ports/Hubs
Hot Swaps
Cellphones
Tablet PC
Set Top Box
PC motherboard
Handheld Devices
TYPICAL APPLICATION
USB
input
4.7uF
Output
IN
OUT
120µF
BL2555 ILIM
R
ILIM
EN
GND
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BL2555
PIN ASSIGNMENT
MARKING INFORMATION
HL
YW
OUT
ILIM
NC
1
2
3
6
5
4
IN
GND
EN
HL: product code
Y: Year code, 1 for 2011, 2 for 2012…
W: Week code, A-Z for 01-26, Ā- for 27-52
DFN2x2-6L
Top View
ABSOLUTE MAXIMUM RATINGS
Parameter
Input Voltage
OUT, ILIM, EN to GND
OUT to GND current
Maximum Power Dissipation
Operating Temperature Range
Storage Temperature
Lead Temperature & Time
Value
-0.3V to 5.5V
-0.3V to VIN+0.3V
Internally limited
1.0 W
-40 - 85C
-40C - 150C
260C, 10S
Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions
may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Vin=5V Ta=25
C,
unless otherwise specified)
Symbol
Vin
V_uvlo
Iq
I_SD
Ron
Parameter
Input Voltage Range
Input UVLO
Input Supply Current
Input Shutdown Current
Power Switch On Resistance
Isw=500mA
Conditions
Rising, hysteresis=25mV
R
ILIM
=20K
Min
2.5
Typ
2.35
320
0.5
95
Max
5.5
Unit
V
V
uA
1.5
145
uA
mohm
mohm
A
A
A
%
Isw=500mA, Tj:
-40C - 120C
R
ILIM
=15K
1.705
1.295
0.520
50
0.8
0.66
160
1.2
R
ILIM
=20K
R
ILIM
=49.9K
Percentage of Limit Current above
Second Current Limit
I
lim
2
Second Current Limit
Threshold
First Current Limit Threshold
First Current Limit Timeout
EN Input Logic High Threshold
EN Input Logic Low Threshold
Thermal Shutdown
I
lim
1
T_lim1
V_enh
V_enl
T_SD
1.6
1
ms
V
V
C
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BL2555
PINOUT DESCRIPTION
PIN #
1
2
3
4
5
6
NAME
OUT
ILIM
NC
EN
GND
IN
DESCRIPTION
Current limit Output. Bypass with a capacitor that is greater than 120F if used for USB
Current limit threshold setting pin. Connect a resistor from this pin to GND to set different
current limit values
No Connect
Enable pin
Ground
Power input. Bypass with a 4.7F capacitor to GND
BLOCK DIAGRAM
IN
Current Limit
+
Reverse-Voltage Block
-
OUT
ILIM
UVLO
THERMAL
SHUT
DOWN
Control
Logic
GND
EN
FUNCTION DESCRIPTION
The BL2555 is a load switch which provides full
protection to systems and loads which may encounter
large current conditions. BL2555 offers a 95mΩ
current-limited switch which can operate over an
input voltage range of 2.5-5.5V. The current limit can
be externally programmed by a precision resistor,
ranges from 75mA to 1.7A.
BL2555 also features reverse voltage blocking, UVLO,
and thermal shutdown to protect IC from overheating.
CURRENT LIMITING
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 at
which the parts will limit is adjustable through the
selection of an external resistor connected to ILIM.
Information for selecting the resistor is found in the
Application Info section.
THERMAL PROTECTION
BL2555 thermal cycles if an overload condition is
present long enough to activate thermal limiting in any
of the above cases. The device turns off when the
junction temperature exceeds 135°C (typ) while in
current limit. The device remains off until the junction
temperature cools 10°C (typ) and then restarts
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BL2555
REVERSE-VOLTAGE BLOCKING
The reverse-voltage protection feature turns off the
Power MOSFET whenever the output voltage exceeds
the input voltage by 150mV (typ) for 4-ms (typ). This
prevents damage to devices on the input side of the
BL2555 by preventing significant current from sinking
into the input capacitance. The BL2555 allow the
power MOSFET to turn on once the output voltage
goes below the input voltage for the same 4-ms
deglitch time.
APPLICATION INFORMATION
INPUT OUTPUT CAPACITANCE
Input and output capacitance improves the performance of the device; the actual capacitance should be optimized for
the particular application. For all applications, a 4.7µF or greater ceramic bypass capacitor between IN and GND is
recommended as close to the device as possible for local noise de-coupling. This precaution reduces ringing on the
input due to power-supply transients. Additional input capacitance may be needed on the input to reduce voltage
overshoot from exceeding the absolute maximum voltage of the device during heavy transient conditions. This is
especially important during bench testing when long, inductive cables are used to connect the evaluation board to the
bench power-supply. Placing a high-value electrolytic capacitor on the output pin is recommended when large
transient currents are expected on the output.
SETTING THE CURRENT LIMIT THRESHOLD
Typical Current Limit (mA)
R
ILIM
(K)
200
138
180
152
151
179
100
266
82
324
68
389
51
520
43
612
30
873
20
1295
15.1
1705
Current Limit Threshold VS RILIM
1800
1600
1400
1200
1000
800
600
400
Current Limit Threshold(mA)
Ilim
200
0
0
50
100
150
Rset(Kohm)
200
250
THERMAL CONSIDERATIONS
During normal operation as a switch, the power dissipated in the part will depend upon the level at which the current
limit is set. The maximum allowed setting for the current limit is 1A and this will result in a power dissipation of,
2
2
P = (ILIM) x RDS = (1) x 0.10 = 100mW
If the part goes into current limit the maximum power dissipation will occur when the output is shorted to ground.
This is more power than the package can dissipate, but the thermal shutdown of the part will activate to protect the
part from damage due to excessive heating. A short on the output will cause the part to operate in a constant current
state dissipating a worst case power of,
P(max) = VIN(max) x ILIM(max) = 5.5 x 1 = 5W
This large amount of power will activate the thermal shutdown and the part will cycle in and out of thermal shutdown
so long as the ON pin is active and the short is present
.
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BL2555
TYPICAL PERFORMANCE CHARACTERISTICS
T=25°C unless specified.
The first and second current limit level
nd
st
Constant current load on BL2555, with 2 current limit level set to 500mA. The 1 current limit level is 50% higher
nd
st
than 2 level, and the 1 level current limiting duration is 1ms.
Blue:
Output Voltage
Red:
Current through
BL2555
Output Short Response
Short BL2552 to GND, and the internal short current limit is shown.
Green:
Input Voltage
Blue:
Output Voltage
Red:
Current through
BL2555
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