Part # N1441 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: ST890: A HIGH SIDE SWITCH FOR PCMCIA AND USB APPLICATIONS


Part Details:

AN1441 APPLICATION NOTE ST890: A HIGH SIDE SWITCH FOR PCMCIA AND USB APPLICATIONS A. Randazzo 1. INTRODUCTION ST890 is a low voltage, P-Channel MOSFET power switch, intended for high side load switchingapplications. Its main applications are PCMCIA slots, Portable Equipment and Access bus slots. ST890is useful in all the applications that need a supply with short-circuit protection and programmable currentlimitation, like the slots in which the cards can be connected and disconnected without turning off thepower supply. 2. FUNCTIONAL DESCRIPTION 2.1. Switch Resistance. Figure 1 shows the internal block diagram of the ST890. The high side Power MOSFET, used as a switch, has an RON lower than 90m at Vcc=3.0V. In the case of a load current of 1A, the drop voltage between the IN and OUT pins is lower than 1A x 0.1=0.1V and, for a switch, it is very important to keepthis drop voltage low. Figure 1: ST890 Internal Block Diagram ST890 IN OUT FAULT - + ON SET + ON- RSET V Obsolete Product(s) - Obsolete Product(s) REF 1.24V ON GND Control Circuitry October 2003 (Rev. 1) 1/9 AN1441 - APPLICATION NOTE Figure 2.1 shows the RON versus the VIN supply voltage. The RON depends on the VIN because the P-Channel MOS is driven by the Vout of the internal error amplifier. Figure 2.1: ON Resistance Versus VIN Supply Voltage ON Resistance vs VIN 100 95 ) 90 ohm 85 m ( 80 )n(o 75 R 70 65 2.5 3 3.5


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