TL7705 datasheet(16/17 Pages) TI

16 / 17 page

Design Tips

Literature Number: SLVAE04

Figure 14. Printed Circuit Layout for the supply voltage supervisor

When using the supply voltage supervisor TL770xB in certain applications a current limiting

resistor R

t (figure 15) in series to the capacitor Ct (pin 3) is required. With this circuit the timing

capacitor will be charged up to the supply voltage V

cc respectively an internal clamping (= 7.1 V),

where the smaller of the these two voltages determines the final voltage at the capacitor. When

the supply voltage drops quickly down to a voltage which is lower than the current voltage at the

capacitor C

t, a parasitic current path may be turned on which in turn erroneously activates the

outputs. This effect is avoided when the mentioned parasitic current I

stays below 1 mA.

Considering this the resistor R

t is calculated as follows:

= ≥

−

max

where V

= threshold voltage of the SENSE input

Ctmax

= V

ccmax or 7 V, the lower of these values apply

When using the TL7705B (V

t = 4.55 V) with a maximum supply voltage Vcc = 5.5 V, one gets:

t = ≥

−

5 5

4 55

950

TL7705 Datasheet(PDF) 16 Page - Texas Instruments