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PDF RT9728B Data sheet ( Hoja de datos )
| Número de pieza | RT9728B | |
| Descripción | 1.8A Power Switch | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT9728B
120mΩ, 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
z USB Bus/Self Powered Hubs
z USB Peripheral Ports
z ACPI Power Distribution
z Battery Power Equipment
z 3G/3.5G Data Card, Set-Top Boxes
Features
z ±10% Current Limit Accuracy @ 1.3A
z Adjustable Current Limit : 75mA to 1.8A (typ.)
z Meets USB Current Limiting Requirements
z Operating Voltage Range : 2.5V to 5.5V
z Reverse Input−Output Voltage Protection
z Built-in Soft-Start
z 120mΩ P-MOSFET
z 120μA Supply Current
z RoHS Compliant and Halogen Free
Ordering Information
RT9728B
Package Type
E : SOT-23-6
QW : WDFN-6L 2x2
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
H : Chip Enable High
L : Chip Enable Low
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.
Simplified Application Circuit
VIN
RFAULT
FAULT Signal
Enable
VIN VOUT
CIN RT9728B
FAULT
ILIM
RILIM
EN/EN GND
VOUT
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS9728B-00 August 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
1 page  
RT9728B
Parameter
Symbol
Test Conditions
Reverse Voltage Comparator
Trip Point (VOUT − VIN)
FAULT Output Low Voltage VOL
FAULT Off State Leakage
IFAULT = 1mA
VFAULT = 5.5V
FAULT Deglitch
FAULT assertion or de-assertion due to
over-current condition
FAULT assertion or de-assertion due to
reverse-voltage condition
Min Typ
-- 135
-- 180
-- 1
5 7.5
24
Max
--
--
--
10
6
Unit
mV
mV
μA
ms
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.
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS9728B-00 August 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
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/Bypass Capacitor
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
RT9728B
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
and FAULT will be asserted accordingly. The under-voltage
lockout detection functions only when the switch is
enabled.
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
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS9728B-00 August 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
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| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT9728B.PDF ] | |
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