RHFL7913A_11 Datasheet, PDF (8/19 Pages) STMicroelectronics – Rad-hard adjustable negative voltage regulator

Device description
5
Device description
RHFL7913A
The RHFL7913A adjustable contains a NPN-type power element controlled by signal
resulting from amplified comparison between internal temperature compensated band-gap
cell and the fraction of the desired output voltage value, generated by an external resistor
divider bridge. The NPN structure allows access to lower drop out levels because its base
current can be routed to ground pin and not to output. To control and monitor the device
from / to the external logic world – usually operating in positive voltage area – a dedicated
logic interface block (INHIBIT and OCM functions) has been implemented with +3 V to +5 V
supplied line V(+). In case V(+) = 0 V, inhibit and OCM functions are not available: In this
condition, INHIBIT function is ON and OCM pin is “no care”. The device is internally
protected by several blocks.
5.1
ADJ pin
The load voltage feed back comes from an external divider resistor bridge middle point to
ADJ pin established between load terminals.
5.2
Inhibit ON-OFF control
When INHIBIT pin is TTL-high (positive), the device switches off current and voltage output.
The device is ON when INHIBIT pin is set TTL-low.
5.3
Overtemperature protection
A temperature detector internally monitors power element junction temperature. The device
goes OFF circa 165 ° - 175 °C are reached, and returns ON when circa 100 °C. When
internal temperature detector reaches 170 °C, the active power element can be at 225 °C:
Device reliability cannot be granted during extensive operation duration with these
conditions.
5.4
Overcurrent protection
I_SC pin. An internal non-fold back short-circuit limitation is set with I_SHORT > 4 A (V_O is 0 V).
This value can be downward modified by an external resistor connected between I_SC and V_I
pins, with a typical value range of 10 kΩ to 200 kΩ. To keep excellent V_O regulation, it is
necessary to set I_SHORT 1.6 times greater than the maximum desired application I_O. When
I_O reaches I_SHORT – 300 mA, the current limitor overrules regulation and V_O starts to drop
and OCM flag is risen. When no current limitation adjustment is required, I_SC pin shall be left
unbiased (as it is in 3 pin packages).
5.5
OCM pin
Goes low when current limitor starts to be active, otherwise V_OCM = V (+). It is bufferized
and can sink 10 mA. OCM pin is internally pulled-up by a 50 kΩ resistor. Can left open when
V (+) = 0.
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Doc ID 12344 Rev 7