BELLING BL2555 Load switch with adjustable current limit Datasheet

BL2555
Load Switch with Adjustable Current Limit
FEATURES
DESCRIPTION
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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.
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
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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.
USB ports/Hubs
Hot Swaps
Cellphones
Tablet PC
Set Top Box
PC motherboard
Handheld Devices
BL2555 is in a tiny DFN2x2-6L package
TYPICAL APPLICATION
Output
USB
input
IN
OUT
120µF
BL2555 ILIM
4.7uF
RILIM
EN
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1
GND
BL2555
MARKING INFORMATION
PIN ASSIGNMENT
OUT
1
6
IN
ILIM
2
5
GND
NC
3
4
EN
HL
YW
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
Value
Input Voltage
OUT, ILIM, EN to GND
OUT to GND current
Maximum Power Dissipation
Operating Temperature Range
Storage Temperature
Lead Temperature & Time
-0.3V to 5.5V
-0.3V to VIN+0.3V
Internally limited
1.0 W
-40 - 85C
-40C - 150C
260C, 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
Parameter
Input Voltage Range
Typ
2.5
Max
Unit
5.5
V
Rising, hysteresis=25mV
2.35
V
Input Supply Current
RILIM=20K
320
uA
Input Shutdown Current
Ron
Power Switch On Resistance
Ilim1
Min
Input UVLO
I_SD
Ilim2
Conditions
Second Current Limit
Threshold
First Current Limit Threshold
T_lim1
First Current Limit Timeout
V_enh
EN Input Logic High Threshold
V_enl
EN Input Logic Low Threshold
T_SD
Thermal Shutdown
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0.5
Isw=500mA
1.5
95
Isw=500mA, Tj: -40C - 120C
uA
mohm
145
mohm
RILIM=15K
1.705
A
RILIM=20K
1.295
A
RILIM=49.9K
0.520
A
50
%
Percentage of Limit Current above
Second Current Limit
0.8
1.2
0.66
ms
1
V
V
160
2
1.6
C
BL2555
PINOUT DESCRIPTION
PIN #
1
NAME
OUT
2
ILIM
3
4
5
6
NC
EN
GND
IN
DESCRIPTION
Current limit Output. Bypass with a capacitor that is greater than 120F 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 4.7F capacitor to GND
BLOCK DIAGRAM
IN
Current Limit
+
Reverse-Voltage Block
-
OUT
ILIM
UVLO
Control
Logic
GND
EN
THERMAL
SHUT
DOWN
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.
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
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
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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)
RILIM (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
Current Limit Threshold(mA)
1800
1600
1400
1200
1000
800
600
Ilim
400
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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BL2555
OUTPUT CAPACITANCE REDUCTION COMPARISION
Test condition, Vin=5V, I_load=2A for 1.5ms, RIlimit=27K
BL2555 response, with Cout=580uF, output voltage drop 2.4V.
Blue:
Output Voltage
Red:
Current through
BL2555
TPS2553 (conventional single level current limit) response, with Cout=580uF, output voltage drop 3.2V.
Blue:
Output Voltage
Red:
Current through
TPS2553
BL2555 response the same voltage drop (3.2V) with only 380uF output capacitance. 33% saved.
Blue:
Output Voltage
Red:
Current through
BL2555
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BL2555
PACKAGE OUTLINE
Package
DFN2x2-6L
Devices per reel
5000
Package specification:
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7
Unit
mm
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