 |
Os motores de busca de Datasheet de Componentes eletrônicos |
|
|
Os motores de busca de Datasheet de Componentes eletrônicos |
|
LM3543M-H Folha de dados(PDF) 9 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LM3543M-H Folha de dados(HTML) 9 Page - National Semiconductor (TI) |
|
|
9 / 12 page  Functional Description (Continued) In Figure 3, port 1 is enabled into a short. When this occurs, the MOSFET switch of port 1 repeatedly opens and closes as the device temperature rises and falls between 145˚C and 135˚C. In this example, the device temperature never rises above 160˚C. The second stage thermal shutdown is not used and port 2 remains operational. When port 1 is enabled into a short in the example illustrated in Figure 4, the device temperature immediately rises above 160˚C. A higher ambient temperature or a larger number of shorted outputs can cause the junction temperature to increase, resulting in the difference in behavior between the current example and the previous one. When the junction temperature reaches 160˚C, all three ports are disabled (port 3 is not shown in the figure) and all three fault-flag signals are asserted. Just prior to time index 2.5 ms, the device temperature falls below 135˚C, all three ports activate, and all three fault flags are removed. The short condition remains on port 1, however. For the remainder of the example, the device temperature cycles between 135˚C and 145˚C, causing port 1 to repeatedly turn on and off but allowing the un-shorted ports to function normally. Soft Start When a power switch is enabled, high levels of current will flow instantaneously through the LM3543 to charge the large capacitance at the output of the port. This is likely to exceed the over-current threshold of the device, at which point the LM3543 will enter its current-limit mode. The amount of current used to charge the output capacitor is then set by the current-limit circuitry. The device will exit the current-limit mode when the current needed to continue to charge the output capacitor is less than the LM3543 current-limit level. Fault Flag The fault flags are open-drain outputs, each capable of sinking up to a 10 mA load current to typically 100 mV above ground. A parasitic diode exists between the flag pins and V IN pins. Pulling the flag pins to voltages higher than V IN will forward bias this diode and will cause an increase in supply current. This diode will also clamp the voltage on the flag pins to a diode drop above V IN. The fault flag is active (pulled low) when any of the following conditions are present: under-voltage, current-limit, or thermal-shutdown. The LM3543 has an internal delay in reporting fault conditions that is typically 7 ms in length. In start-up, the delay gives the device time to charge the output capacitor(s) and exit the current-limit mode before a flag signal is set. This delay also prevents flag signal glitches from occurring when brief changes in operating conditions momentarily place the LM3543 into one of its three error conditions. If an error condition still exists after the delay interval has elapsed, the appropriate fault flag(s) will be asserted (pulled low) until the error condition is removed. In most applications, the 7 ms internal flag delay eliminates the need to extend the delay with an external RC delay network. Application Information Output Filtering The schematic in Figure 1 showed a typical application circuit for the LM3543. The USB specification requires 120 µF at the output of each hub. A three-port hub with 33 µF tantalum capacitors at each port output meets the specification. These capacitors provide short-term transient current to drive downstream devices when hot-plug events occur. Capacitors with low equivalent-series-resistance should be used to lower the inrush current flow through the LM3543 during a hot-plug event. The rapid change in currents seen during a hot plug event can generate electromagnetic interference (EMI). To reduce this effect, ferrite beads in series between the outputs of the LM3543 and the downstream USB port are recommended. Beads should also be placed between the ground node of the LM3543 and the ground nodes of connected downstream ports. In order to keep voltage drop across the beads to a minimum, wire with small DC resistance should be used through the ferrite beads. A 0.01 µF - 0.1 µF ceramic capacitor is recommended on each downstream port directly between the V bus and ground pins to further reduce EMI effects. Power Supply Filtering A sizable capacitor should be connected to the input of the LM3543 to ensure the voltage drop on this node is less than 330 mV during a heavy-load hot-plug event. A 33 µF, 16V 10125825 FIGURE 3. Thermal Shutdown Characteristics when only the First-Stage Thermal-Shutdown Mode is Needed 10125826 FIGURE 4. Thermal Shutdown Characteristics when Both First-Stage and Second-Stage Thermal-Shutdown Modes are Needed www.national.com 9 |
Nº de peça semelhante - LM3543M-H |
|
Descrição semelhante - LM3543M-H |
|
|
|
Ligação URL |
| Privacy Policy |
| ALLDATASHEETPT.COM |
| ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
Portuguese ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
