 |
Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
|
Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
SMH4802 Datasheet(PDF) 8 Page - Summit Microelectronics, Inc. |
|
||||||||||||||||||||||||||||||
SMH4802 Datasheet(HTML) 8 Page - Summit Microelectronics, Inc. |
|
|
8 / 20 page  8 SMH4802 2062 2.3 6/19/03 SUMMIT MICROELECTRONICS, Inc. Preliminary Information APPLICATIONS INFORMATION Powering VDD The 12V shunt regulator between the VDD and VSS pins allows the SMH4802 to operate over a wide range of supply voltages. It is necessary to use a series dropping resistor (RD) between the host power supply and the VDD pininordertobiastheshuntregulatorandlimitcurrentintothe device. System Enable The EN/TS input provides an active high comparator input that may be used as a master enable or temperature sense input. Under-/Over-Voltage Sensing The Under-Voltage (UV) and Over-Voltage (OV) inputs provide a set of comparators that act in conjunction with an external resistor divider network to sense when the host supply voltage exceeds the user defined limits. If the input to the UV pin rises above 2.5V, and the input to the OV pin falls below 2.5V, the power-up sequence may be initiated. If UV falls below 2.5V, or OV rises above 2.5V, the PG# and VGATE outputs will be shut down immediately. Under-/Over-Voltage Filtering The SMH4802 may also be configured so that an out of tolerance condition on UV/OV will not shut off the output immediately. A filter delay can be inserted so that only sustained under-voltage or over-voltage conditions will shut off the output. An out of tolerance condition on UV/ OV for longer than the filter delay time (tUOFLTR) will latch the VGATE and PG outputs in the off state if the UV/OV filter option is enabled. The Under-/Over-Voltage Filter- ing feature is disabled in the default configuration of the device. Under-Voltage Hysteresis The Under-Voltage comparator input may be configured with a programmable level of hysteresis. The compare level may be set in steps (up to 15) of 62.5mV below 2.5V. The default under-voltage hysteresis level is set to 62.5mV. Soft Start Slew Rate Control Once all of the preconditions for powering up the DC/DC converters have been met, the SMH4802 provides a means to soft start the external power FET limiting the in-rush current. Current limiting is generally needed due to the bulk capacitance across the power rails of the DC/DC convert- ers. The VGATE output of the SMH4802 is current limited to IVGATE, allowing the slew rate to be easily modified using external passive components. Load Control — Turning on a DC/DC Converter Once power has been ramped to the DC/DC converter, two conditions must be met before the PG# output can be asserted: the DRAIN SENSE voltage must be below 2.5V, and the VGATE voltage must be greater than V DD – VGT. The DRAIN SENSE input ensures the power MOSFET is not absorbing too much steady state power from operat- ing at a high V DS. (This sensor remains active at all times, except during the current regulation period). The VGATE sensor ensures the power MOSFET is operating well into its saturation region before allowing the loads to be switched on. Once VGATE reaches V DD – V GT this sensor is latched. After the external MOSFET is properly switched on, the PG# output will be asserted after a delay of t PGD. The delay time is programmable from 5ms to 160ms. NOTE: The PG# output has a 12V withstand capability, so high voltages must not be connected to this pin. A bipolar transistor or an opto-isolator can be used to boost the withstand voltage to that of the host supply. Force Shutdown — Secondary Feedback The Force Shutdown signal (FS#) is an active low input that provides a method of receiving feedback from the secondary side of the DC/DC controllers. A built-in hold- off timer allows the SMH4802 to ignore the state of the FS# input until the time period expires. The FS# input must be driven high by the end of this time period. If not, a low level on this input will shut off the VGATE and PG# outputs. The purpose of the hold-off timer is to allow enough time for devices on the secondary side of the DC/DC controller to power-up and stabilize. This unique feature of the SMH4802 allows supervisory circuits, such as an SMS44, to control the shutdown of the primary side soft start circuit, even though the secondary side initially has no power. Circuit Breaker Operation The SMH4802 provides a number of circuit breaker functions to protect against over current conditions. A sustained over-current event could damage the host supply and/or the load circuitry. The board’s load current passes through a series resistor (R S) connected between the MOSFET source (which is tied to CBSENSE) and V SS. The breaker trips (Figure 4) whenever the voltage drop across R S is greater than 50mV for more than t CBD (a programmable filter delay ranging from 10µs to 500µs). |
Número de pieza similar - SMH4802 |
|
Descripción similar - SMH4802 |
|
|
|
Enlace URL |
| Política de Privacidad |
| ALLDATASHEET.ES |
| ¿ALLDATASHEET es útil para Ud.? [ DONATE ] |
Todo acerca de Alldatasheet | Publicidad | Contáctenos | Política de Privacidad | Intercambio de Enlaces | 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 |
Spanish ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
