GS-R120251.5 Просмотр технического описания (PDF) - STMicroelectronics

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производитель

GS-R120251.5

1.8W TO 8W STEP-DOWN SWITCHING REGULATOR FAMILY

STMicroelectronics 

USER NOTES

Input Voltage

The recommended operating maximum DC Input Voltage is 15V inclusive of ripple voltage.

GS-R12P

Inhibit function

The inhibit feature allows to put in stand-by mode the device.

With INH pin 4 higher than 2.2V the device is disabled and the power consumption is reduced to less than

100µA for Vi = 15V.

With INH pin lower than 0.8V, the device is enabled.

If the INH pin is left floating, an internal pull up ensures that the voltage at the pin reaches the inhibit threshold

and the device is disabled.

The pin is also Vi compatible.

Current protection

The device has two current limit protections, pulse by pulse and frequency fold back.

The current is sensed through a resistor and if reaches the threshold, the on time is reduced and consequently

the output voltage too.

Since the minimum switch ON time (necessary to avoid false overcurrent signal) is not enough to obtain a suf-

ficiently low duty cycle at 250 Hz, the output current, in strong overcurrent or short circuit conditions, could in-

crease again.

For this reason the switching frequency is also reduced, so keeping the inductor current under its maximum

threshold.

The frequency depends on the feedback voltage.

As the feedback voltage decreases (due to the reduced duty cycle), the switching frequency decrease too.

Thermal shutdown

The shutdown block generates a signal that turns off the power stage if the temperature of the internal chip goes

higher than a fixed internal threshold (150 ºC).

The sensing element of the chip is very close to the PDMOS area, so ensuring an accurate and fast temperature

detection.

An hysteresis of approximately 20ºC avoids that the devices turns on and off continuously.

Thermal Characteristics

Output voltage programming (GS-R12H(S)0001.5 only)

The GS-R12P output voltage is 5.54V ±4%, to reduce this value connect a resistor between pin 6 (FB) and

pin 5 (Vout-c).

The resistor must be located very close to the proper pins, to minimize the injected noise (see figure 1).

The resistor value is calculated using the following formula:

Rv=[(Vout-1.235)*11.3]/(5.54-Vout) --[kOhm]

Vout can be adjusted between 1.235V (Rv=0 Ohm) and 5.54V (Rv=open)

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