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LT1161 数据表(PDF) 8 Page - Linear Technology |
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LT1161 数据表(HTML) 8 Page - Linear Technology |
8 / 12 page 8 LT1161 1161fa APPLICATIONS INFORMATION Low Voltage/Wide Supply Range Operation When the supply is <12V, the LT1161 charge pumps do not produce sufficient gate voltage to fully enhance stan- dard N-channel MOSFETs. For these applications, logic- level MOSFETs can be used to extend operation down to 8V. If the MOSFET has a maximum VGS rating of 15V or greater, then it can also be used up to the 60V (absolute maximum) rating of the LT1161. MOSFETs are available from both Motorola and Siliconix which meet these criteria. Protecting Against Supply Transients The LT1161 is 100% tested and guaranteed to be safe from damage with 60V applied between the V+ and ground pins. However, when this voltage is exceeded, even for a few microseconds, the result can be a catastrophic failure. For this reason it is imperative that the LT1161 not be exposed to supply transients above 60V. For proper current-sense operation, the V+ pins are re- quired to be connected to the positive side of the drain sense resistors (see Drain Sense Configuration). There- fore, the best way to prevent supply transients is to ensure that the supply is adequately decoupled at the point where the V+ pins and drain sense resistors meet. Several hundred microfarads may be required with high current switches. When operating voltages approach the 60V absolute maxi- mum rating of the LT1161, local supply decoupling be- tween the V+ pins (11, 20) and ground pins (1, 10) is highly recommended. A small ferrite bead between the supply connection and local capacitor can also be effective in suppressing transients. Note however, that resistance should not be added in series with the V+ pins because it will cause an error in the current sense threshold. Fault Feedback Two methods can be used to derive switch status. First, the timer pin voltage can be monitored to indicate when the switch is turned off due to current limit. During normal operation (ON or OFF), the timer voltage is 3.5V and only during current limit does the voltage drop below 3V. The second method shown in Figure 8 uses a quad exclusive-NOR gate to indicate when the output of the switch has not obeyed the input command (i.e., output low when it should be high or vice versa). In addition to current limit, this gives a fault indication if the switch is shorted or if the load is open. Figure 8. Fault Feedback Using Exclusive-NOR Gate 24V RS ROL ADD FOR OPEN-LOAD DETECTION 1161 F08 FAULT INPUT 1/4 MM74HC266A 100k LT1161 V+ V+ DS G IN LOAD Low-Side Driving Although the LT1161 is primarily targeted at high-side (grounded load) switch applications, it can also be used for low-side (supply-connected load), or mixed high- and low-side switch applications. Figures 9a and 9b illustrate LT1161 switch channels driving low-side power MOSFETs. Because the LT1161 charge pump tries to pump the gate of the N-channel MOSFET above supply, a clamp zener is required to prevent the VGS (absolute maximum) of the MOSFET from being exceeded. The LT1161 gate drive is current limited for this purpose so that no resistance is needed between the gate pin and zener. Figure 9a. Low-Side Driver with Load Current Sensing 100 µF IRFZ44 1 µF RS 0.01 Ω (PTC) 1161 F09a 15V 1N4744 LT1161 12V TO 48V V+ V+ DS G 4A LOAD T + |
类似零件编号 - LT1161 |
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类似说明 - LT1161 |
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