BL2553 BL2553

BL2553
BL2553
Precision Load Switch
with Adjustable Current Limit
DESCRIPTION
APPLICATION
The BL2553 is a load switch which provides full
protection to systems and loads which may
encounter large current conditions. BL2553 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. BL2553 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. The
BL2553 will not turn off after a current limit fault, but
will rather remain in the constant current mode
indefinitely. The nFAULT output asserts low during
over-current and reverse-voltage conditions.
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USB ports/Hubs
Hot Swaps
Cellphones
Tablet PC
Set Top Box
PC motherboard
Handheld Devices
FEATURES
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Up to 1.5A Max Load current
Accurate Current-limit threshold: +/-5%
Programmable Current-limit : 75mA to 1.7A
Fast Over-Current Response
Fault Flag Output: nFAULT Pin
Reversed Current blocking
Thermal Shutdown, UVLO protection
Tiny DFN2x2-6L Package
BL2553 is housed in a tiny DFN2x2-6L package。
TYPICAL APPLICATION
1
BL2553
PIN CONFIGURATION
OUT 1
ILIM
6
ABSOLUTE ＭAXIMUM RATINGS
IN
2
5
GND
nFAULT 3
4
EN
(Note: Exceeding these limits may damage the device. Exposure to
absolute maximum rating conditions for long periods may affect device
reliability.)
IN to GND…..............................................–0.3V to 6V
OUT, ILIM, nFAULT, EN to GND…..–0.3V to VIN+0.3V
OUT to GND Current …………………..Internally limited
Maximum Power Dissipation………….…………...1.0W
Operating Temperature Range …….…. –40°C to 85°C
Storage Temperature Range….………–55°C to 150°C
ELECTRICAL CHARACTERISTICS
(VIN = 5V, unless otherwise specified. Typical values are at TA = 25oC.)
PARAMETER
Input Voltage Range
Input UVLO
Input Supply Current
Input Shutdown Current
Power Switch On Resistance
Current limit Threshold
Response time to Short-circuit
Reverse-voltage Threshold
Reverse Leakage Current
EN Input Logic High threshold
EN Input Logic Low threshold
nFAULT Output Low Voltage
nFAULT Output Leakage
nFAULT Deglitch Time
Thermal Shutdown
Thermal Shutdown In Current
Limit
Thermal Shutdown Hysteresis
CONDITIONS
MIN
2.5
Rising, Hysteresis=25mV
RILIM=20K
TYP
2.35
120
0.5
95
ISW =500mA
ISW =500mA, -40°C≤TJ≤120°C
RILIM=15K
RILIM=20K
RILIM=49.9K
MAX
5.5
1.5
145
1.705
1.295
0.520
1
150
0.5
VOUT-VIN
VOUT=5.5V,Vin=0V,VEN=High
VnFAULT=5.5V
2
1
0.66
InFAULT =1mA
70
De-assertion due to Over-current
De-assertion due to Reverse-Voltage
9
4.5
160
135
15
170
1
UNITS
V
V
A
A
m
m
A
A
A
S
mV
A
V
V
mV
A
mS
o
o
o
C
C
C
2
BL2553
PIN DESCRIPTION
PIN #
NAME
1
OUT
2
ILIM
3
nFAULT
4
5
6
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
Fault flagging pin. Connect a pull up resistor to IN, when in fault conditions, this pin
is asserted low
Enable pin
Ground
Power input. Bypass with a 4.7F capacitor to GND
FUNCTION DESCRIPTION
The BL2553 is a load switch which provides full
protection to systems and loads which may
encounter large current conditions. BL2553 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.
BL2553 also features reverse voltage blocking,
UVLO, and thermal shutdown to protect IC from
overheating. An nFAULT flag output provides a
pull-down signal to indicate fault conditions.
the input side of the BL2553 by preventing
significant current from sinking into the input
capacitance. The BL2553 allow the power
MOSFET to turn on once the output voltage goes
below the input voltage for the same 4-ms
deglitch time. The reverse-voltage condition also
asserts the nFAULT output (active-low) after 4-ms.
During “OFF” condition, the reverse-voltage
blocking function is still in effect, preventing any
current floating from OUT to IN even when the
device is not in use.
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. BL2553 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
nFAULT FLAG
The FAULT open-drain output is asserted (active
low) during an overcurrent, over temperature or
reverse-voltage condition. The BL2553 asserts the
FAULT signal until the fault condition is removed
and the device resumes normal operation. The
nFAULT signal is de-asserted once device power is
cycled or the enable is toggled and the device
resumes normal operation. The BL2553 and
BL2553is designed to eliminate false nFAULT
reporting by using an internal delay "deglitch"
circuit for overcurrent (9-ms typ) and
reverse-voltage (4.5-ms typ) conditions without
the need for external circuitry. This ensures that
nFAULT is not accidentally asserted due to
normal operation such as starting into a heavy
capacitive load. The deglitching circuitry delays
entering and leaving fault conditions. Over
temperature conditions are not deglitched and
assert the nFAULT signal immediately.
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
3
BL2553
BLOCK DIAGRAM
IN
Current
Limit
Reverse-Voltage Block
nFAULT
+
-
OUT
ILIM
+
EN
THERMAL
SHUT
DOWN
-
UVLO
Control
Logic
GND
TYPICAL PERFORMANCE CHARACTERISTICS
Turn on Delay and Rise time
VIN=5V, RILIM=20K, ROUT=5Ω
CH1: Output Voltage; CH2: Enabled pin Voltage; CH4: Input Current
Device Enabled into short-Circuit
VIN=5V, RILIM=20K, ROUT=0Ω
CH2: Enabled pin Voltage; CH4: Input Current
Turn off Delay and Fall Time
VIN=5V, RILIM=20K, ROUT=5Ω
CH1: Output Voltage; CH2: Enabled pin Voltage; CH4: Input Current
Device Enabled into short-Circuit
VIN=5V, RILIM=20K, ROUT=0Ω
CH2: Enabled pin Voltage; CH4: Input Current
4
BL2553
Full Load to Short-Circuit
Short-Circuit to Full load
VIN=5V, RILIM=20K
VIN=5V, RILIM=20K
CH1: Output Voltage; CH2: nFault pin Voltage; CH4: Input Current CH1: Output Voltage; CH2: nFault pin Voltage; CH4: Input Current
No-load to Short-Circuit
VIN=5V, RILIM=20K
CH1: Output Voltage; CH2: nFAULT pin Voltage;
CH4: Input Current
No-load to 1 Ω-load
VIN=5V,RILIM=20K
CH1: Output Voltage; CH2: nFAULT pin Voltage
CH4: Input Current
Short-Circuit to No-load VIN=5V,RILIM=20K
CH1: Output Voltage;
CH2: nFAULT pin Voltage; CH4: Input Current
1 Ω-load to No-load
VIN=5V,RILIM=20K
CH1: Output Voltage; CH2: nFAULT pin Voltage
CH4: Input Current
5
BL2553
Input Voltage from 0V into 5V
Input Voltage from 5V into 0V
VOUT=5V, RILIM=20K, ROUT=10Ω
CH1: Output Voltage; CH2: nFAULT pin Voltage
CH3: Input Voltage; CH4: Input Current
VOUT=5V, RILIM=20K, ROUT=10Ω
CH1: Output Voltage; CH2: nFAULT pin Voltage
CH3: Input Voltage; CH4: Input Current
Switch current VS Drain-Source Voltage
Switch current VS Drain-Source Voltage
1400
300
1200
250
Ids(mA)
Ids(mA)
1000
800
600
200
150
100
400
200
50
Vin=5V,Rset=20K
Vin=5V,Rset=100K
0
0
0
200
400
600
800
1000
Vin-Vout(mV)
0
200
400
600
Vin-Vout(mV)
800
1000
Switch current VS Drain-Source Voltage
160
140
Ids(mA)
120
100
80
60
40
20
Vin=5V,Rset=200K
0
0
500
1000
1500
Vin-Vout(mV)
6
BL2553
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.
Current Limit Threshold VS RILIM
1800
Current Limit Threshold(mA)
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
1600
1400
1200
1000
800
600
Ilim
400
200
0
0
50
100
150
Rset(Kohm)
200
250
POWER DISSIPATION
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,
P = (ILIM)2 x RDS = (1)2 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.
7
BL2553
PACKAGE OUTLINE
8