Electronic Components Datasheet Search |
|
MC3392T Datasheet(PDF) 7 Page - Motorola, Inc |
|
MC3392T Datasheet(HTML) 7 Page - Motorola, Inc |
7 / 12 page MC3392 7 MOTOROLA ANALOG IC DEVICE DATA Over Temperature Shutdown Internal Thermal Shutdown Circuitry is provided to protect the MC3392 in the event the Operating Junction Temperature (TJ) exceeds 150°C. Typically, Thermal Shutdown will occur at 160 ° to 170°C. The thermal shutdown sense element is embedded within the output PNP (Q4) in order to afford very fast thermal coupling of Q4 to the sense element. Any rise in temperature due to the ambient is translated directly to Q4 and the sense element. If the junction temperature rises excessively above 150 °C, the Thermal Shutdown circuit will turn ON, quickly pulling the gate of Q2 to ground, which pulls the base of Q4 to ground, turning it OFF. In addition, the Thermal Shutdown circuit simultaneously turns Q5 ON and with a suitable pull–up resistor at the Fault pin reports the presence of a fault (logic low). The output PNP will remain OFF until the junction temperature decreases to within the operating range at which time Thermal Shutdown turns OFF, ceasing to hold the gate of Q2 low, turning Q4 back ON. This process will repeat as long as the thermal over load exists. This mode of operation is a nondestructive safety feature of the device and will correct itself real time when the cause of over temperature is removed. A continued over temperature condition will thermally Pulse Width Modulate (PWM) the output and Fault and may be incorrectly interpreted as an oscillating load if one does not consider the simultaneous performance of the Fault pin. Current Limit The MC3392 protects itself against Vout to +VS hard shorts as well as any over current conditions by reducing the magnitude of output current (IO) to that of the short circuit current limit value (ISC). When the output current monitored by Q3 tries to exceed ISC, the Current Limit circuit lowers the gate voltage of Q2, lowering the base of Q4, causing the load current through Q4 to diminish. Simultaneously, when the load current exceeds ISC, Q5 will turn ON reporting a fault condition. If the output current is allowed to remain excessively high for the degree of heatsinking incorporated, and the junction temperature of the device is allowed to heat beyond 150 °C, the Thermal Shutdown circuit will activate and the output will thermally PWM. Again, these modes of operation are safety features of the MC3392 and are not destructive. Overvoltage Detect This circuitry protects the MC3392 from Vout voltages in excess of 16 V by lowering the output current to a nondestructive value. With increasing Vout voltage (16 V < Vout < 45 V) the load current is reduced to below that of ISC and produces a fold back current effect. As Vout increases in excess of 16 V, the output current decreases linearly until Vout exceeds 45 V. With an infinite heatsink and Vout > 45 V, IO will be less than 100 mA. For the other extreme, no heatsink and Vout > 45 V, IO can be expected to be less than about 400 mA. This behavior of IO in relation to Vout is shown in Figure 13. For the infinite heatsink case, the output current initially increases with increased voltage until Vout exceeds 16 V, thereafter the behavior is expressed as, IO = ISC [1–(Vout –16 V) / 30 V] Beyond 45 V, IO is limited to less than 100 mA. Anytime the Overvoltage Detect circuit is activated, the gate of Q5 is pulled low causing Q5 to turn ON to report the fault at the Fault pin. Inductive Load Clamp The MC3392 has an internal inductive load clamp for protection against flyback voltages imposed on the output pin in excess of 70 V. The incorporated zener clamp can quickly dissipate up to 60 milli–Joules of inductive flyback energy. Figure 14 shows the maximum inductive load versus load current that the clamp can handle safely. As an example (using Figure 14), if operating the MC3392 to drive a 0.33 H inductor, the maximum load current should be adjusted to 600 mA or less. If the load current is too high for the inductor used, some series resistance can be added to the load to limit the current. If this is not possible, an external clamp must be used to facilitate handling the higher energy. When using an external clamp, the external clamp voltage must be less than 60 V so as to override the internal clamp. The output clamp offers protection for the output when the MC3392 is in the OFF state. During the ON state, other protection features (Overvoltage, Current, and Temperature) are available to protect the output. Fault Logic The Fault is comprised of an internal open drain FET requiring an external pull–up resistor. Typically, a 5.0 k pull–up resistor to a +5.0 V supply is satisfactory. The Fault pin is afforded a minimum of 2000 V ESD protection (Human Body Model) by virtue of the 7.2 V zener diode. The Fault will report a fault (logic low state) whenever the MC3392 experiences a fault condition. Conditions producing a fault are: IO > 1.3 A (over current/shorted load); TJ > 150°C (over temperature); and Vout > 16 V (overvoltage). If the device goes into Thermal Shutdown, caused by environmental overheating (not resulting from another fault condition), the Fault and Vout will thermally PWM as the MC3392 repeatedly heats to shut off, cools, and again turns on. If a current limit fault causes the device to go into Thermal Shutdown, the output will oscillate while the Fault remains pulled low. There is no thermal hysteresis designed in to control the PWM effect and this fault mode of operation is not destructive. Fast Turn–Off This circuitry enhances the MC3392 turn–off performance. Whenever Vin goes to a logic low state, Vout is held in an OFF state for approximately 15 µs. During fast turn–off, less than 30 mA of current is allowed to flow producing an abrupt turn–off. This turn–off characteristic can be seen in Figure 12, a photograph of the typical turn–off waveform. |
Similar Part No. - MC3392T |
|
Similar Description - MC3392T |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |