L9758

Functional description

Doc ID 14273 Rev 3

23/29

5.6

RESET monitors

when the reset pin (RST5 or RSTL) is released. RST5 and RSTL use separate timers. This

delay is programmable via an external resistor connected to RST_TIM pin. A value of 4.7 k

Ω

corresponds to 1 ms and 47 k

Ω to 10 ms. All values in between are linear approximated.

The timer delay is common however the attack and release times are only dependant on the

5.7

Thermal protection

The tracking regulators incorporate thermal limit with shutdown. When the junction

temperature reaches the shutdown threshold, if there is a tracking regulator in current

limitation, it switches off and all the other regulators stay on. When the temperature

decrease the regulator restarts. The over temperature shutdown has an hysteresis to avoid

thermal pumping.

5.8

Reference current

The L9758 provides a DC voltage at the REXT pin. An external resistor to ground creates a

reference current which is mirrored internally for use in the device.

The reference current is used to supply all the analog blocks and to charge and discharge

an integrated capacitor to generate a 5 MHz clock for the switching functionality.

Figure 3.

Current reference generator

The circuit is designed for a 10 k

Ω resistor. For all affected parameters, this resistor value is

mentioned in the electrical characteristics section.

V

ref

+

-

R

ext

Iref

Iref

V

ref

+

-

R

ext

Iref

Iref