RHFL4913XX15

Device description

DocID028784 Rev 1

21/32

7

Device description

The device fixed voltage contains a PNP type power element controlled by a signal

resulting from the amplified comparison between the internal temperature compensated

bandgap cell and the fraction of the desired output voltage value. This fractional value is

obtained by an internal-to-die resistor divider bridge set by STMicroelectronics. The device

embeds current limit and thermal protection circuits.

7.1

Low pin count package limitations

Some functions (INHIBIT, OCM, SENSE) are not available due to lack of pins on the

SMD.5 and TO-257 packages. Corresponding die pads are by default connected inside the

silicon.

7.2

SENSE pin

The load voltage is connected to SENSE pin by a Kelvin line: voltage feedback comes from

the internal divider resistor bridge. Therefore, possible output voltages are set by

manufacturer's mask metal options. SENSE pin is not available in 3-pin packages.

7.3

Inhibit ON-OFF control

By setting INHIBIT pin TTL-high, the device switches off the output current and voltage.

The device is on when INHIBIT pin is set low. Since INHIBIT pin is internally pulled down, it

can be left floating in case inhibit function is not used. INHIBIT pin is not available in 3-pin

packages.

7.4

Overtemperature protection

A temperature detector internally monitors the power element junction temperature. The

device goes off at 175 °C and it is again on mode when it is at 135 °C.

When the internal temperature detector reaches 175 °C, the active power element can be

at 225 °C: the device reliability cannot be granted in case of extensive operation beyond

these conditions.

7.5

Overcurrent protection

An internal foldback short-circuit limitation is set with ISHORT typically higher than 3.8 A (VO

is 0 V). This value can be reduced by an external RSH resistor connected between ISC pin

and VI

pin, with a typical value range from 25 kΩ to 200 kΩ. Lower values can be used, but

the sample-to-sample spread for the given value increases. This adjustment feature is not

available in 3-pin packages. To keep excellent VO regulation, ISHORT should be set 1.6 times

greater than the maximum desired application IO. When IO reaches ISHORT

– 300 mA, the

current limiter overrules regulation, VO starts to drop and the OCM flag rises. When no

current limitation adjustment is required, ISC pin must be left un-biased (as it is in 3-pin

packages). To choose the proper value of the RSH resistor, refer to Figure 35: "Short-circuit

current vs. RSH" and Figure 36: "Short-circuit current vs. RSH (magnification)".