FS6407 datasheet(55/111 Pages) NXP

55 / 111 page

NXP Semiconductors

FS6407/FS6408

6.7.8

Start-up sequence

To provide a safe and well known start-up sequence, the FS6407/FS6408 includes an undervoltage lock-out. This undervoltage lock-out

is only applicable when the device is under a Power-On-Reset condition, which means the initial condition is VSUP < VSUP_UV_L (i.e. below

2.7 V max). In all the other conditions (i.e. LPOFF), the device is able to operate (and therefore to restart) down to VSUP_UV_L. The other

different voltage rails automatically start, as described in Figure 39.

Figure 39. Start-up scheme

The final value of VAUX and VCCA depends on the hardware configuration (resistor values on the SELECT pin). The typical start up

sequence takes around 16 ms to release RSTB. RSTB can be pulled low after those 16 ms by the MCU, if it is not ready to run after power

up. If an internal or external fault happen during this start up phase (ABIST fault due to regulator shorted for example), the 8.0 s timer

monitoring the RSTB pin low, finally sends the device in Deep Fail-safe mode after 8.0 s.

~16ms

Vsup

Vint_2.5

Vpre

Vsup_uv_5

UV Lock-out

Vpre_uv

Vpre_EN

Vcca/Vaux

Vcore

RSTB

INTB

(Vddio=Vcore)

Select pin

1ms

LBIST

120us

1ms

FS6407 Datasheet(PDF) 55 Page - NXP Semiconductors