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PDF RT9721A Data sheet ( Hoja de datos )
| Número de pieza | RT9721A | |
| Descripción | 500mA High-Side Power Switches | |
| Fabricantes | RichTek | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RT9721A (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
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RT9721A/B
80mΩ, 500mA High-Side Power Switches with Flag
General Description
Features
The RT9721A/B are low voltage, single N-MOSFET high-
side power switches, optimized for self-powered and bus-
powered Universal Serial Bus (USB) applications. The
RT9721A/B series provides a charge pump circuitry to drive
the internal MOSFET switch; the switch's low RDS(ON),
80mΩ, meets USB voltage drop requirements; and a flag
output is available to indicate fault conditions to the local
USB controller.
Additional features include soft-start to limit inrush current
during plug-in, thermal shutdown to prevent catastrophic
switch failure from high-current loads, under-voltage lockout
(UVLO) to ensure that the device remains off unless there
is a valid input voltage present. The maximum current is
limited to typically 750mA in dual ports in accordance with
the USB power requirements, lower quiescent current as
50uA making this device ideal for portable battery-operated
equipment.
z Compliant to USB Specifications
z Built-In N-MOSFET
` Typical RDS(ON) : 80mΩ
z Output Can Be Forced to Higher Than Input (Off-
State)
z Low Supply Current :
` 50μA Typical at Switch On State
` 0.1μA Typical at Switch Off State
z Guaranteed 500mA Continuous Load Current
z Wide Input Voltage Ranges : 2.5V to 5.5V
z Open-Drain Fault Flag Output
z Hot Plug-In Application (Soft-Start)
z 2.15V Typical Under-Voltage Lockout (UVLO)
z Current Limiting Protection
z Thermal Shutdown Protection
z Reverse Current Flow Blocking (no body diode)
z UL Approved−E219878
z RoHS Compliant and Halogen Free
The RT9721A is designed without output auto-discharge
function and RT9721B is designed with output auto-
discharge function.
The RT9721A/B are available in SOT-23-5 package
requiring minimum board space and smallest components.
Applications
z USB Bus/Self Powered Hubs
z USB Peripherals
z Notebook, Motherboard PCs
Ordering Information
RT9721
Pin Configurations
(TOP VIEW)
Package Type
B : SOT-23-5
Lead Plating System
G : Green (Halogen Free and Pb Free)
VOUT
5
FLG
4
23
Output Discharge Function
A : Without Auto-Discharge Function
B : With Auto-Discharge Function
VIN GND EN
SOT-23-5
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.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
DS9721A/B-02 April 2011
www.richtek.com
1
1 page  
Typical Operating Characteristics
On Resistance vs. Input Voltage
110
IOUT = 100mA
105
100
95
90
85
80
2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Switch On Supply Current vs. Input Voltage
45
No Load
42.5
40
37.5
35
32.5
30
27.5
25
2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Switch Off Supply Current vs. Input Voltage
0.30 No Load
0.25
0.20
0.15
0.10
0.05
0.00
2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
DS9721A/B-02 April 2011
RT9721A/B
On Resistance vs. Temperature
150
VIN = 5V, IOUT = 100mA
130
110
90
70
50
-50
-25
0 25 50 75
Temperature (°C)
100 125
Switch On Supply Current vs. Temperature
45.0 VIN = 5V, No Load
42.5
40.0
37.5
35.0
32.5
30.0
27.5
25.0
-50
-25
0 25 50 75
Tmeperature (°C)
100 125
Switch Off Supply Current vs. Temperature
0.8 VIN = 5V, No Load
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-50
-25
0 25 50 75
Temperature (°C)
100 125
www.richtek.com
5
5 Page 
RT9721A/B
Voltage Drop
The USB specification states a minimum port-output voltage
in two locations on the bus, 4.75V output of a Self-Powered
Hub port and 4.4V output of a Bus-Powered Hub port. As
with the Self-Powered Hub, all resistive voltage drops for
the Bus-Powered Hub must be accounted for to guarantee
voltage regulation (see Figure 7-47 of Universal Serial
Specification Revision 2.0 ).
The following calculation determines VOUT(MIN) for multiple
ports (NPORTS) ganged together through one switch (if using
one switch per port, NPORTS is equal to 1) :
VOUT(MIN) = 4.75V − [ II x (4 x RCONN + 2 x RCABLE) ] −
(0.1A x NPORTS x RSWITCH) − VPCB
Where
RCONN : Resistance of connector contacts (two contacts
per connector)
RCABLE : Resistance of upstream cable wires (one 5V and
one GND)
RSWITCH : Resistance of power switch (80mΩ typical for
RT9721A/B)
VPCB : PCB voltage drop
The USB specification defines the maximum resistance
per contact (RCONN) of the USB connector to be 30mΩ
and the drop across the PCB and switch to be 100mV.
This basically leaves two variables in the equation : the
resistance of the switch and the resistance of the cable.
If the hub consumes the maximum current (II) of 500mA,
the maximum resistance of the cable is 90mΩ.
The resistance of the switch is defined as follows :
RSWITCH = { 4.75V − 4.4V − [ 0.5A x (4 x 30mΩ + 2 x
90mΩ)] − VPCB} / (0.1A x NPORTS)
= (200mV − VPCB ) / (0.1A x NPORTS )
If the voltage drop across the PCB is limited to 100mV,
the maximum resistance for the switch is 250mΩ for four
ports ganged together. The RT9721A/B, with its maximum
110mΩ on-resistance over temperature, easily meets this
requirement.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of IC
package, PCB layout, the rate of surroundings airflow and
temperature difference between junction to ambient. The
maximum power dissipation can be calculated by following
formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
Where TJ(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT9721A/B, the maximum junction temperature is 125°C.
The junction to ambient thermal resistance θJA is layout
dependent. For SOT-23-5 package, the thermal resistance
θJA is 250°C/W on the standard JEDEC 51-3 single layer
thermal test board. The maximum power dissipation at TA
= 25°C can be calculated by following formula :
PD(MAX) = (125°C - 25°C) / (250°C/W) = 0.4W for
SOT-23-5 package
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal resistance
θJA. For the RT9721A/B, Figure 1 shows the maximum
power dissipation allowed under various ambient
temperatures.
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
Single Layers PCB
SOT-23-5
25 50 75 100
Ambient Temperature (°C)
125
Figure 1. Maximum Power Dissipation Derating Curve
DS9721A/B-02 April 2011
www.richtek.com
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet RT9721A.PDF ] | |
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