VISHAY SI4779CY

Si4779CY
New Product
Vishay Siliconix
High-Side N-Channel Switch with Current Limit
FEATURES
APPLICATIONS
D
D
D
D
D
D
D
D
D
User Set Over Current Limit From 400 mA to 2.4 A
Low rDS(on) 45 mW (max) at 25_C
Fault Indicator
Under Voltage Lockout
Notebook Computers Power Management
USB Power Distribution
Hot Plug In Power Supplies
Power Supply/Load Protection
Battery-Charger Circuits
DESCRIPTION
The Si4779CY n-channel high-side switch combines a low
rDS(on) MOSFET switch with a user set, pulse gate control
(PGC) based current limit. This switch is designed to protect
the system power supply from overloads and short circuit
conditions in applications such as USB. The PGC based
approach to the current limiter provides the additional benefit
of keeping the MOSFET junction temperature within
specification, thereby eliminating the need for thermal
shutdown. The low quiescent current makes the Si4779CY
ideal for use in battery powered devices. The Si4779CY
operates on both 3-V and 5-V busses, and is packaged in the
LITTLE FOOTr SO-8 package.
FUNCTIONAL BLOCK DIAGRAM
OUT
IN
–
+
FAULT
Control
Circuit
SET
VR
ON
GND
See page 7 for a detailed block diagram.
Document Number: 71664
S-04276—Rev. A, 16-Jul-01
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Si4779CY
Vishay Siliconix
New Product
ABSOLUTE MAXIMUM RATINGS (TA = 25_C UNLESS OTHERWISE NOTED)
Parameter
Symbol
Steady State
Voltage, IN to GND
VIN
–0.3 to 7
Voltage, ON
VON
–0.3 to 7
Continuous Drain Current (TJ = 150rC)
r a
Maximum Power Dissipationa
TA = 25rC
TA = 85rC
TA = 70rC
Operating Junction and Storage Temperature Range
Unit
V
2.4
ID
A
2.4
PD
0.65
W
Tj, Tstg
–65 to 125
_C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation
of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING CONDITIONS
Parameter
Voltage, IN to GND
Symbol
Steady State
VIN
3.0 to 5.0
Voltage, ON or FAULT to GND
VON, VFAULT
0 to 5.0
Operating Temperature Range
TA
0 to 85
Unit
V
_C
THERMAL RESISTANCE RATINGS
Parameter
Junction-to-Ambienta
Junction-to-Foot (Drain)b
Steady State
Symbol
Typical
Maximum
RthJA
98
120
RthJF
37
46
Unit
_
_C/W
Notes
a. Surface mounted on 1” x1” FR4 board, 0.062” thick, 2-oz copper double sided.
b. Junction-to-foot thermal impedance represents the effective thermal impedance of all heat carrying leads in parallel and is intended for use in conjunction with
the thermal impedance of the PC board pads to ambient (RthJA = RthJF + RthPCB-A). It can also be used to estimate chip temperature if power dissipation and
the lead temperature of a heat carrying (drain) lead is known.
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Document Number: 71664
S-04276—Rev. A, 16-Jul-01
Si4779CY
New Product
Vishay Siliconix
SPECIFICATIONS
Test Conditions Unless Specified
Parameter
Typa
Max
Unit
5.5
V
VIN = 4.75 V, ID = 2 A
0.035
0.045
VIN = 3.0 V, ID = 2 A
0.045
0.055
Min
TA = 25_C, VIN = 5 V
Symbol
Limits
Basic Operations
Operating Voltage
VIN
On-State Resistance
2.7
rDS(on)
Supply Current
ON Input Low Voltage
ON Input High Voltage
ISUP(off)
ON = IN, VIN = 5.5 V, VOUT = 0 V
2
ISUP(on)
ON = GND, VIN = VOUT = 5.5 V, IOUT = 0 A
70
VONL
VIN = 2.7 to 5.5 V
VONH
ON Input Current
W
m
mA
0.8
VIN = 2.7 to 3.6 V
2.0
VIN = 4.5 to 5.5 V
2.4
ION
VON = 5.5 V
Over Current Limit Rangeb
ILIMIT
Tolerance = "20%, VIN = 5 V
Under Voltage Lockout (falling edge)
UVLO
V
0.01
"1
mA
2.4
A
Protection
2.0
2.3
DUVLO
Under Voltage Hysteresis
FAULT Output Voltage
0.4
Lowb
FAULT Logic Output Leakage Current
2.6
0.1
VFAULT
ISINK = 100 mA
IFL
VIN = VFAULT = 5.5 V
V
0.4
0.01
mA
1
Dynamicb
Turn-On Time
ton
Rise Time
Turn-Off Time
3
VIN = 5 V, RL = 11 W,
W CL = 40 m
mF
tr
ms
3.5
toff
Fall Time
1.5
VIN = 5 V, IOUT = 500 mA
tf
Cycle Time
VIN = 5 V, RL = 0.5 W
tcyc
m
ms
0.5
8
ms
Notes
a. Typical values at TA = 25_C are for DESIGN AID ONLY, not guaranteed nor subject to production testing.
b. Guaranteed by design. Derived from ISET current ratio, current-limit amplifier and external set resistor accuracy.
TIMING DIAGRAMS
ON
50%
ON
50%
ON
ON
90%
50%
OUT
50%
OUT 10%
OUT
ton
toff
FIGURE 1.
Document Number: 71664
S-04276—Rev. A, 16-Jul-01
90%
OUT
10%
trise
tfall
FIGURE 2.
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Si4779CY
New Product
Vishay Siliconix
TIMING DIAGRAMS
ON
VRSET
ILIMIT
tcyc
FIGURE 3.
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
RSET vs. ILIMIT
2.5
I LIMIT (A)
2.0
VIN = 5 V
1.5
1.0
0.5
RSET value is measured in circuit
0.0
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
RSET (W)
Supply Current, Output Disalble vs.
Ambient Temperature Over Operating Voltage
Normalized On-Resistance
vs. Ambient Temperature
1.4
1000
r DS(on) – On-Resistance ( W)
(Normalized)
ON Input Current (nA)
VIN = 5.5 V
100
10
1.2
1.0
0.8
0.6
1
–40
–20
0
20
40
60
TA – Ambient Temperature (_C)
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4
80
100
0.4
–40
–25
–10
5
20
35
50
65
80
95
TA – Ambient Temperature (_C)
Document Number: 71664
S-04276—Rev. A, 16-Jul-01
Si4779CY
New Product
Vishay Siliconix
TYPICAL WAVEFORMS (VIN = 5 V, TA = 25_ UNLESS OTHERWISE NOTED)
20 ms/div
1 ms/div
CH1:
CH2:
CH3:
IOUT, 2 A/div
VOUT, 5 V/div, CL = 47 mF
ON, 5 V/div
FIGURE 4. Switch Turn-ON/OFF Time
50 ms/div
CH1:
CH2:
CH3:
IOUT, 0.5 A/div
VOUT, 5 V/div, CL = 10 mF
ON, 5 V/div
FIGURE 5. Switch Turn-ON Time
200 ms/div
CH1:
CH2:
CH3:
IOUT, 0.5 A/div
VOUT, 5 V/div, CL = 10 mF
ON, 5 V/div
CH1:
CH2:
CH3:
IOUT, 0.5 A/div
VOUT, 5 V/div, CL = 150 mF
ON, 5 V/div
NOTE: Discharge time based primarily on external R and C
NOTE: Discharge time based primarily on external R and C
FIGURE 6. Switch Turn-OFF Time
FIGURE 7. Switch Turn-OFF Time
Document Number: 71664
S-04276—Rev. A, 16-Jul-01
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Si4779CY
Vishay Siliconix
New Product
TYPICAL WAVEFORMS (VIN = 5 V, TA = 25_ UNLESS OTHERWISE NOTED)
2 ms/div
CH1:
CH2:
CH3:
CH4:
2 ms/div
ON, 5 V/div
VOUT, 5 V/div, RL = 0.5 W, CL = 47 mF
FAULT, 5 V/div
IOUT, 1 A/div
FIGURE 8. FAULT to Short Response (tcyc)
2 ms/div
CH1:
CH2:
CH3:
CH4:
FIGURE 10. Power Supply Droops vs. Short
6
ON, 5 V/div
VRESET, 500 mV/div
VOUT, 5 V/div, RL = 5.6 W, CL = 100 mF
IOUT, 1 A/div
FIGURE 9. VRESET to Over Current Response
2 ms/div
ON, 5 V/div
PS Droops, 50 mV/div, Offset = 5 V
VOUT, 1 V/div, RL = 0.5 W, CL = 100 mF
IOUT, 0.5 A/div
NOTE: Special test with 820-mF capacitor at PS and RSET
setup for 0.5 A.
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CH1:
CH2:
CH3:
CH4:
CH1:
CH2:
CH3:
CH4:
ON, 5 V/div
PS Droops, 100 mV/div, Offset = 5 V
VOUT, 1 V/div, RL = 0.5 W, CL = 100 mF
IOUT, 2 A/div
NOTE: Special test with 820-mF capacitor at PS and RSET
setup for 2.4 A.
FIGURE 11. Power Supply Droops vs. Short
Document Number: 71664
S-04276—Rev. A, 16-Jul-01
Si4779CY
New Product
Vishay Siliconix
PIN CONFIGURATION
PIN DESCRIPTION
SO-8
IN
1
8
OUT
IN
2
7
OUT
ON
3
6
FAULT
ET
4
5
GND
Si4778DY
Top View
Pin
Symbol
Description
1, 2
IN
Input. N-channel MOSFET drain, bypass IN with a 100-mF capacitor to GND.
3
ON
Active-low switch-on input, logic low turns switch on. ON needs to be connected to
VIN during power up, then connect to GND to activate the switch after power up.
4
SET
Current-limit input. A resistor from SET to GND sets the current limit for the switch.
5
GND
Ground
6
FAULT
7, 8
OUT
Fault indicator output. This open drain output goes low when the circuit is in current
limit or in short circuit protection mode.
Switch output. N-channel MOSFET source.
DETAILED BLOCK DIAGRAM
1
8
IN
IN
OUT
2
7
OUT
–
+
UVLO
EA
CP
BG
3
ON
QB
Q
S
R
+
6
FAULT
–
D
+
–
4
SET
5
GND
RSET
FIGURE 12.
Document Number: 71664
S-04276—Rev. A, 16-Jul-01
www.vishay.com
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Si4779CY
New Product
Vishay Siliconix
DETAILED DESCRIPTION
The SI4779CY limits the output current to a user-defined level.
When the output current passes through the main switch a
fraction of this current passes through a replica switch and
RSET.
time off is based on average power consumption, which is
designed to be kept under 500 mW.
If the output is shorted , the circuit will go into an on-off cycle
to protect the switch and to prevent the battery from draining
down.
RSET is an external sense resistor used to set the level of the
over current limit; the over current limit should be set between
0.4 A and 2.4 A (see graph for RSET value vs. current limit).
The circuit shuts down the switch when the current flowing
through the switch exceeds Ilimit. After a short period of time,
the circuit will slowly turn on the switch again. The length of
The fault output (FAULT) goes low when the circuit is in over
current limit or short circuit protection mode. A 100-kW pull-up
resistor from FAULT to IN provides a logic-control signal.
APPLICATIONS DIAGRAM
Line Input
Line Output
OUT
IN
100 mF
100 kW
FAULT
100 kW
Si4779CY
ON
100 mF
11 W
ON
SET
GND
RSET
FIGURE 13.
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Document Number: 71664
S-04276—Rev. A, 16-Jul-01