关于LM3526

您好，

现在正使用LM3526设计一个USB控制器。

对datasheet中的参数OCthresh Over-current Threshold， Isc Short Circuit Output Current的意思不是很明白。

表中说的2.2AOCthresh是两个port还是一个port？这两个参数哪个是Figure 8 (page 5)中的Current Limit？

我想知道每个port的最大输出电流是多少？

谢谢！

Copy here for other guys:

http://e2e.ti.com/support/power_management/simple_switcher/f/858/t/260159.aspx

Agreed that the description and conditions in the datasheet are not very good.

Input supply must be able to supply the rated currents (Isc and OCthresh), otherwise the Error flag may not trip during a true fault condition. For devices with multi-channels, the input supply must be able to supply the rated Isc current for all channels (Isc x n) for the time needed to charge the output capacitors.

When the Enable pin is switched On the pass element will begin to turn on. With the output connected to a fully discharged capacitor, the output current will ramp from 0mA to the controlled Isc value (1.2A typical). This controlled charge time could be considered a form of 'Soft-Start'. The time needed to charge the output capacitor can be approximated from the formula:

      t = (Vin x (Cout / Isc))

In the case where Vin is 5.00V, Cout is 220uF, and Isc is 1.2A

            t = (5.00 x (220e-6 / 1.2)

            t = 0.9ms

The internal circuitry considers the output capacitor fully charged when the output current demand is less than the controlled Isc value (Iout < Isc).

If the output capacitor is not charged within typically 1ms (toc), the error flag will go low.

The output current will continue to flow at the controlled Isc rate and the error flag will stay low until either: 1) the output capacitor becomes fully charged, or 2) the Enable pin is switched Off.

It is important to note that if the input supply is not able to supply the full Isc value for the time needed to charge the output capacitor(s), the output current will be less than the controlled Isc value for one, or more, channels. This will cause one, or more, of the error flags to stay high even though the output capacitor is not fully charged.

If the output capacitor becomes fully charged, the error flag will return to the high state, the controlled Isc current rate will end, and the higher Over-Current threshold (OCthresh) will become active.

In a normal situation each port is rated for 500mA.