RT9728B
®
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Features
±±
±±
±10% Current Limit Accuracy @ 1.3A
Adjustable Current Limit : 75mA to 1.8A (typ.)
Meets USB Current Limiting Requirements
Operating Voltage Range : 2.5V to 5.5V
Reverse Input−−
−−
−Output Voltage Protection
Built-in Soft-Start
120mΩΩ
ΩΩ
Ω P-MOSFET
120μμ
μμ
μA Supply Current
RoHS Compliant and Halogen Free
120mΩΩ
ΩΩ
Ω, 1.8A Power Switch with Adjustable Current Limit
General Description
The RT9728B is a cost effective, low voltage, single
P-MOSFET power switch IC for USB application with a
adjustable current limit feature. Low switch-on resistance
(typ. 120mΩ) and low supply current (typ. 120μA) are
realized in this IC. The RT9728B can offer a adjustable
current limit threshold between 75mA and 1.8A (typ.) via
an external resistor. The ±10% current limit accuracy can
be realized for all current limit settings. In addition, a flag
output is available to indicate fault conditions to the local
USB controller. Furthermore, the chip also integrates an
embedded delay function to prevent mis-operation due to
high inrush current. The RT9728B is an ideal solution for
USB power supplies and can support flexible applications
since it is suitable for various current limit requirements.
It is available in the SOT-23-6 and WDFN-6L 2x2 packages.
Applications
USB Bus/Self Powered Hubs
USB Peripheral Ports
ACPI Power Distribution
Battery Power Equipment
3G/3.5G Data Card, Set-Top Boxes
Simplified Application Circuit
Ordering Information
Note :
Richtek products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
RT9728B
Package Type
E : SOT-23-6
QW : WDFN-6L 2x2
H : Chip Enable High
L : Chip Enable Low
Lead Plating System
G : Green (Halogen Free and Pb Free)
VIN
RT9728B
VIN
ILIM
RILIM
VOUT
FAULT
EN/EN
RFAULT
CIN
VOUT
GND
FAULT Signal
Enable
RT9728B
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Marking Information
Pin Configuration
(TOP VIEW)
SOT-23-6 WDFN-6L 2x2
VOUT ILIM
VIN GND
4
23
56
FAULT
EN/EN
VOUT
ILIM
VIN
GND
5
4
1
2
3
6
GND
7EN/ENFAULT
Pin No. Pin Name Pin Functi on
SOT-23-6 WDFN-6L 2x2
1 6 VIN Power input.
2 5,
7 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
3 4
EN/EN Enable control input.
4 3
FAULT Active-low open-drain output. Asserted during over-current,
over-temperature, or reverse-voltage conditions.
5 2 ILIM
Current limit setting. Connect an external resistor to set current
limit threshold. 15k RILIM 232k is recommended.
6 1
VOUT Power switch output.
Functional Pin Description
1Q : Product Code
W : Date Code
RT9728BLGQW
RT9728BLGE
0J= : Product Code
DNN : Date Code
0K= : Product Code
DNN : Date Code
RT9728BHGE
1R : Product Code
W : Date Code
RT9728BHGQW
0K=DNN 0J=DNN
1RW 1QW
RT9728B
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Functional Block Diagram
UVLO
Current
Limit
7.5ms
Deglitch
4ms
Deglitch
Thermal
Sense
Drive
Reverse Voltage
Comparator
Switch
well
Current
Sense
+
-
VOUT
ILIM
GND
EN/EN
VIN
FAULT
Operation
The RT9728B is a current-limited power switch using
P-MOSFET for applications where short-circuit or heavy
capacitive loads will be encountered. These devices allow
users to adjust the current limit threshold between 75mA
and 1.8A (typ.) via an external resistor. Additional device
shutdown features include over-temperature protection and
reverse-voltage protection.
The RT9728B provides built-in soft-start function. The driver
controls the gate voltage of the power switch. The driver
incorporates circuitry that controls the rising time and
falling time of the output voltage to limit large inrush current
and voltage surges. The RT9728B enters constant-current
mode when the load exceeds the current limit threshold.
RT9728B
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Electrical Characteristics
(VIN = 3.6V, 15kΩ ≤ RILIM ≤ 232kΩ, TA = 25°C, unless otherwise specified)
Parameter Symbol Test Conditions Min Typ Max Unit
EN Input Voltage
Logic-High VIH 1.1 -- --
V
Logic-Low VIL -- -- 0.66
Current Limit Threshold
Resistor Range RILIM (nominal 1%) from ILIM to GND 15 -- 232 k
Under-Voltage Lockout
Threshold VUVLO VIN rising -- 2.3 -- V
VIN falling -- 2.1 --
Shutdown Current ISHDN V
IN = 3.6V, no load on VOUT, VEN = 0V -- 1 3 A
Quiescent Current IQ VIN = 5.5V,
no load on VOUT
RILIM = 20k -- 120 170
A
RILIM = 210k -- 120 170
Reverse Leakage Current IREV V
OUT = 5V, VIN = 0V -- 1 10 A
Thermal Shutdown Threshold TSD -- 160 -- °C
Static Drain-Source On-State
Resistance RDS(ON) I
SW = 0.2A -- 120 -- m
Current Limit ILIM
RILIM = 20k 1166 1295 1425
mA
RILIM = 49.9k 468 520 572
RILIM = 210k 104 130 156
ILIM shorted to VIN -- 75 --
Absolute Maximum Ratings (Note 1)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- −0.3V to 6V
Other Pins------------------------------------------------------------------------------------------------------------------- −0.3V to 6V
Power Dissipation, PD @ TA = 25°C
SOT-23-6 -------------------------------------------------------------------------------------------------------------------- 0.4W
WDFN-6L 2x2 -------------------------------------------------------------------------------------------------------------- 0.606W
Package Thermal Resistance (Note 2)
SOT-23-6, θJA --------------------------------------------------------------------------------------------------------------- 250°C/W
WDFN-6L 2x2, θJA --------------------------------------------------------------------------------------------------------- 165°C/W
WDFN-6L 2x2, θJC -------------------------------------------------------------------------------------------------------- 7°C/W
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- 260°C
Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions (Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.5V to 5.5V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
RT9728B
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Parameter Symbol Test Conditions Min Typ Max Unit
Reverse Voltage Comparator
Trip Point (VOUT VIN) -- 135 -- mV
FAULT Output Low Voltage VOL IFAULT = 1mA -- 180 -- mV
FAULT Off State Leakage VFAULT = 5.5V -- 1 -- A
FAULT Deglitch
FAULT assertion or de-assertion due to
over-current condition 5 7.5 10
ms
FAULT assertion or de-assertion due to
reverse-voltage condition 2 4 6
Note 1. Stresses beyond those listed “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 may
affect device reliability.
Note 2. θJA is measured at TA = 25°C on a low effective thermal conductivity single-layer test board per JEDEC 51-3. θJC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
RT9728B
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Typical Application Circuit
VIN
RT9728B
VIN
ILIM
RILIM
VOUT
150µF
FAULT
EN/EN
RFAULT
CIN
VOUT
GND
FAULT Signal
100k
10µF
Enable
RT9728B
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Typical Operating Characteristics
Supply Current vs. Temperature
80
90
100
110
120
130
140
150
-50 -25 0 25 50 75 100 125
Temperature (°C)
Supply Current (μA
)
Fault Deglitch Timing vs. Temperature
5
6
7
8
9
10
-50 -25 0 25 50 75 100 125
Temperature (°C)
Fault Deglitch Timing (ms
)
Under Voltage Lock out vs. Tempe rature
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
-50 -25 0 25 50 75 100 125
Temperature (°C)
Under Voltage Lockout (V
)
Rising
Falling
EN/EN Threshold Voltage vs. Temperature
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
-50 -25 0 25 50 75 100 125
Temperature (°C)
EN/EN Threshold Voltage (V) 1
Rising
Falling
On- Resistance vs. Temperature
60
70
80
90
100
110
120
130
140
150
-50-25 0 255075100125
Temperature (°C)
On-Resistance (m )
Ω
VIN = 3.6V
VIN = 5V
Current Lim it vs. Temperature
1.1
1.2
1.3
1.4
1.5
1.6
-50 -25 0 25 50 75 100 125
Temperature (°C)
Current Limit (A)
RILIM = 20kΩ
RT9728B
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Current Limit
Time (2.5ms/Div)
Short Circuit to Full Load (5Ω)
VOUT
(2V/Div)
Fault
(5V/Div)
IIN
(1A/Div)
VIN = 5V, COUT = 150μF,
RILIM = 20kΩ
VOUT
(2V/Div)
Fault
(5V/Div)
IIN
(1A/Div)
Current Limit
Time (2.5ms/Div)
VIN = 5V, COUT = 150μF,
RILIM = 20kΩ
Full Load (5Ω) to Short Circuit
Power On from EN
Time (500μs/Div)
VOUT
(5V/Div)
VEN
(10V/Div)
IIN
(1A/Div)
RT9728BH, VIN = 5V, COUT = 150μF,
RILIM = 20kΩ, ROUT = 5Ω
Power Off from EN
Time (500μs/Div)
VOUT
(5V/Div)
VEN
(10V/Div)
IIN
(1A/Div)
RT9728BH, VIN = 5V, COUT = 150μF,
RILIM = 20kΩ, ROUT = 5Ω
Power Off from EN
Time (500μs/Div)
VOUT
(5V/Div)
VEN
(10V/Div)
IIN
(1A/Div)
RT9728BL, VIN = 5V, COUT = 150μF,
RILIM = 20kΩ, ROUT = 5Ω
Power On from EN
Time (500μs/Div)
VOUT
(5V/Div)
VEN
(10V/Div)
IIN
(1A/Div)
RT9728BL, VIN = 5V, COUT = 150μF,
RILIM = 20kΩ, ROUT = 5Ω
RT9728B
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Static Drain-Source Current vs. VIN - VOUT
0
20
40
60
80
100
120
140
160
0 200 400 600 800 1000
VIN - VOUT (mV)
Static Drain-Source Current (mA) 1
VIN = 5.5V, RILIM = 200kΩ
Static Drain-Source Current vs. VIN - VOUT
0
200
400
600
800
1000
1200
1400
1600
0 200 400 600 800 1000
VIN - VOUT (mV)
Static Drain-Source Current (mA)1
VIN = 5.5V, RILIM = 20kΩ
Current Limit
Short Circuit to No Load
VOUT
(2V/Div)
Fault
(5V/Div)
IIN
(1A/Div)
VIN = 5V, COUT = 150μF,
RILIM = 20kΩ
Time (2.5ms/Div)
Current Limit
Time (2.5ms/Div)
No Load to Short Circuit
VOUT
(2V/Div)
Fault
(5V/Div)
IIN
(1A/Div)
VIN = 5V, COUT = 150μF,
RILIM = 20kΩ
RT9728B
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Applications Information
The RT9728B is a single P-MOSFET power switch with
an active-high/low enable input, optimized for self-powered
and bus-powered Universal Serial Bus (USB) applications.
The switch's low RDS(ON) meets USB voltage drop
requirements and a flag output is available to indicate fault
conditions to the local USB controller.
Current Limit and Short-Circuit Protection
When a heavy load or short-circuit situation occurs while
the switch is enabled, a large transient current may flow
through the device. The RT9728B includes current-limit
circuitry to prevent the MOSFET switch and the hub
downstream ports from damage due to large transient
current. The RT9728B provides an adjustable current limit
threshold between 120mA and 1.8A (typ) via an external
resistor, RILIM, whose resistance is between 15kΩ and
232kΩ. However, if the ILIM pin is connected to VIN, the
current limit threshold will be 75mA (typ). Once the current
Figure 1. Current Limit Threshold vs. RILIM
limit threshold is exceeded, the device enters constant-
current mode until either thermal shutdown occurs or the
fault is removed. Figure 1 shows the curve of current limit
value vs. RILIM resistor. The recommended RILIM resistor
selection is shown in Table 1.
Table 1. Recommended RILIM Resistor Selection
Ω
Current Limit Threshold vs. RILIM
0
250
500
750
1000
1250
1500
1750
2000
0 30 60 90 120 150 180 210 240
RILIM (k )
Current Limit Threshold (mA
)
Desired Nominal
Current Limit (mA ) Ideal Resistor
(k) Clo set 1%
Resistor (k) Actual Limits (Include R Tolerance)
IOS Min (mA) IOS Nom (mA) IOS Max (mA)
75 Short ILIM to VIN 50.0 75.0 100.0
120 226.1 226.0 101.3 120.0 142.1
200 134.0 133.0 173.7 201.5 233.9
300 88.5 88.7 262.1 299.4 342.3
400 65.9 66.5 351.1 396.7 448.7
500 52.5 52.3 443.9 501.6 562.4
600 43.5 43.2 535.1 604.6 674.1
700 37.2 37.4 616.0 696.0 776.0
800 32.4 32.4 708.7 800.8 892.9
900 28.7 28.7 797.8 901.5 1005.2
1000 25.8 26.1 875.4 989.1 1102.8
1100 23.4 23.2 982.1 1109.7 1237.3
1200 21.4 21.5 1057.9 1195.4 1332.9
1300 19.7 19.6 1158.0 1308.5 1459.0
1400 18.5 18.7 1225.7 1385.0 1544.3
1500 17.3 17.4 1317.3 1488.5 1659.7
1600 16.2 16.2 1414.8 1598.7 1782.6
1700 15.2 15.0 1528.1 1726.7 1925.3
1800 14.4 14.3 1602.9 1811.2 2019.5
RT9728B
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Fault Flag
The RT9728B provides a FAULT signal pin which is an
open-drain N-MOSFET output. This open-drain output is
pulled low when current exceeds current limit threshold.
The FAULT output is capable of sinking a 1mA load to
180mV (typ.) above ground. The FAULT pin requires a
pull-up resistor; this resistor should be large in value to
reduce energy drain. A 100kΩ pull-up resistor works well
for most applications. In case of an over-current condition,
FAULT will be asserted only after the flag response delay
time, tD, has elapsed. This ensures that FAULT is asserted
upon valid over-current conditions and that erroneous error
reporting is eliminated. For example, false over-current
conditions may occur during hot-plug events when
extremely large capacitive loads are connected, which
induces a high transient inrush current that exceeds the
current limit threshold. The FAULT response delay time,
tD, is typically 7.5ms.
Supply Filter/Bypa ss Ca pa citor
A 10μF low ESR ceramic capacitor connected from VIN to
GND and located close to the device is strongly
recommended to prevent input voltage drooping during hot-
plug events. However, higher capacitor values may be used
to further reduce the voltage droop on the input. Without
this bypass capacitor, an output short may cause sufficient
ringing on the input (from source lead inductance) to
destroy the internal control circuitry. Note that the input
transient voltage must never exceed 6V as stated in the
Absolute Maximum Ratings.
Output Filter Capacitor
A low ESR 150μF aluminum electrolytic capacitor
connected between VOUT and GND is strongly
recommended to meet the USB standard maximum droop
requirement for the hub, VBUS. Standard bypass methods
should be used to minimize inductance and resistance
between the bypass capacitor and the downstream
connector to reduce EMI and decouple voltage droop
caused by hot-insertion transients in downstream cables.
Ferrite beads in series with VBUS, the ground line and
the 0.1μF bypass capacitors at the power connector pins
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
SOT-23-6 packages, the thermal resistance, θJA, is 250°C/
W on a standard JEDEC 51-3 single-layer thermal test
board. For WDFN-6L 2x2 packages, the thermal
resistance, θJA, is 165°C/W on a standard JEDEC 51-3
single-layer thermal test board. The maximum power
are recommended for EMI and ESD protection. The bypass
capacitor itself should have a low dissipation factor to allow
decoupling at higher frequencies.
Chip Enable Input
The RT9728BH/L is disabled when the EN/EN pin is in a
logic-low/high condition. During this condition, the internal
circuitry and MOSFET are turned off, reducing the supply
current to 1μA typically. The maximum guaranteed voltage
for a logic-low at the EN/EN pin is 0.66V. A minimum
guaranteed voltage of 1.1V at the EN/EN pin will turn off
the RT9728B. Floating the input may cause unpredictable
operation. EN/EN should not be allowed to go negative
with respect to GND.
Under-Voltage Lockout
Under-Voltage Lockout (UVLO) prevents the MOSFET
switch from turning on until input voltage exceeds
approximately 2.3V. If input voltage drops below
approximately 2.1V, UVLO turns off the MOSFET switch.
RT9728B
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Figure 2. Derating Curve of Maximum Power Dissipation
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0 25 50 75 100 125
Ambient Temperature (°C)
Maximum Power Dissipation (W) 1
WDFN-6L 2x2
SOT-23-6
Single-Layer PCB
dissipation at TA = 25°C can be calculated by the following
formula :
PD(MAX) = (125°C − 25°C) / (250°C/W) = 0.400W for
SOT-23-6 package
PD(MAX) = (125°C − 25°C) / (165°C/W) = 0.606W for
WDFN-6L 2x2 package
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. The derating curves in Figure 2 allow the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
RT9728B
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Outline Dimension
AA1
e
b
B
D
C
H
L
SOT-23-6 Surface Mount Package
Dimensions In Millimeters Dimensions In Inches
Symbol Min Max Min Max
A 0.889 1.295 0.031 0.051
A1 0.000 0.152 0.000 0.006
B 1.397 1.803 0.055 0.071
b 0.250 0.560 0.010 0.022
C 2.591 2.997 0.102 0.118
D 2.692 3.099 0.106 0.122
e 0.838 1.041 0.033 0.041
H 0.080 0.254 0.003 0.010
L 0.300 0.610 0.012 0.024
RT9728B
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Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Customers should obtain the latest relevant information and data sheets before placing orders and should verify
that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek
product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use;
nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent
or patent rights of Richtek or its subsidiaries.
Dimensions In Millimeters Dimensions In Inches
Symbol Min Max Min Max
A 0.700 0.800 0.028 0.031
A1 0.000 0.050 0.000 0.002
A3 0.175 0.250
0.007 0.010
b 0.200 0.350 0.008 0.014
D 1.950 2.050 0.077 0.081
D2 1.000 1.450 0.039 0.057
E 1.950 2.050 0.077 0.081
E2 0.500 0.850 0.020 0.033
e 0.650 0.026
L 0.300 0.400
0.012 0.016
W-Type 6L DFN 2x2 Package
D
1
E
A3
A
A1
eb
L
D2
E2
SEE DETAIL A
11
2
2
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
DETAIL A
Pin #1 ID and Tie Bar Mark Options
