TPS40007

TPS40009

SLUS589B− NOVEMBER 2003 − REVISED FEBRUARY 2005

11

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APPLICATION INFORMATION

SETTING THE CURRENT LIMIT

Connecting a resistor from VDD to ILIM sets the current limit. A 15-

µA current sink internal to the device causes

tolerance of the current sink is too loose to do an accurate current limit. The main purpose is for hard fault

MOSFET, it is generally possible to apply a load that thermally damages the converter. This device is intended

for embedded converters where load characteristics are defined and can be controlled.

A local capacitor (with a value 50 pF to 150 pF) placed across the resistor between VDD and ILIM may improve

coupling a common mode noise between VDD and ILIM.

SOFT-START AND SHUTDOWN

These two functions are combined on the SS/SD pin. There is a VBE offset (0.65-V) between the external SS/SD

pin and internal soft-start voltage at the error amplifier input, allowing the device to be enabled before starting

and allows for a smooth startup with no overshoot of the output voltage.

t − Time − 1 ms/div

FB

(200 mV/ div)

SS/SD

(200 mV/ div)

Figure 5. Offset Between SS/SD and FB at Startup