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Revision 1.04

11 - 20

AS1390A, AS1390B

Datasheet - D e t a i l e d D e s c r i p t i o n

8.1.2

Undervoltage-Lockout (UVLO)

To enable the usage of the circuit with a wide input voltage range (typ. 12V and 24V), the threshold for undervoltage detection should be

selectable by external components. Therefore a PAD UVLO is implemented, with an external resistor that selects the value of the threshold and

implements also a hysteresis. Till UVLOCO gets deactivated, the threshold is higher, after UVLOCO is 0 (no undervoltage condition), the

threshold is lowered by a switch-on of a constant current source.

If the undervoltage-lockout is not needeed connect the UVLO pin to VDDL.

Figure 19. UVLO - comparator and external resistor divider

Figure 20. UVLO - comparator Output

Following equations can be derived for adjusting the threshold voltages.

Undervoltage threshold High:

Undervoltage threshold High:

Where:

(EQ 3)

V

DDH

UVH

–

V

REF

1

R

UVLO1

R

UVLO2

-------------------

+









×

=

(EQ 4)

V

DDH

UVL

–

V

REF

1

R

UVLO1

R

UVLO2

-------------------

+









×

I

HYST

R

UVLO1

×

(

)

–

=