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TDA3668

Very low dropout voltage/quiescent current 5 V regulator with overvoltage switch off

Philips Electronics 

Philips Semiconductors

Very low dropout voltage/quiescent current

5 V regulator with overvoltage switch off

Preliminary specification

TDA3668AT

EXAMPLE 1

The regulator is stabilized with an electrolytic capacitor of

68 µF (ESR = 0.5 Ω). At Tamb = −40 °C, the capacitor

value is decreased to 22 µF and the ESR is increased

to 3.5 Ω. The regulator will remain stable at a temperature

of Tamb = −40 °C.

EXAMPLE 2

The regulator is stabilized with an electrolytic capacitor of

10 µF (ESR = 3.3 Ω). At Tamb = −40 °C, the capacitor

value is decreased to 3 µF and the ESR is increased to

20 Ω. The regulator will remain stable at a temperature of

Tamb = −40 °C.

EXAMPLE 3

The regulator is stabilized with a 100 nF MKT capacitor

connected to the output. Full stability is guaranteed when

the output current is larger then 200 µA. Because the

thermal influence on this capacitor value is almost zero,

the regulator will remain stable at a temperature of

Tamb = −40 °C.

For successful operation of the IC (maximum output

current capability) special attention has to be given to the

PCB ground plane required as heatsink, the thermal

capacity of the heatsink and its ability to transfer heat to

the external environment. For the SO8 package it is

possible to reduce the total thermal resistance from

125 to 50 K/W.

APPLICATION CIRCUIT WITH BACKUP FUNCTION

Sometimes a backup function is needed to supply, for

example, a microcontroller for a short period of time when

the supply voltage spikes to 0 V (or even −1 V).

This function can easily be built with the TDA3668AT by

using an output capacitor with a large value. When the

supply voltage is 0 V (or −1 V), only a small current will

flow into pin REG from this output capacitor (a few µA).

The application circuit is given in Fig.7.

EXAMPLE 4

The regulator is stabilized with a 100 nF capacitor in

parallel with an electrolytic capacitor of 10 µF connected to

the output.

The regulator is now stable under all conditions and

independent of:

• The ESR of the electrolytic capacitor

• The value of the electrolytic capacitor

• The output current.

Application circuits

The maximum output current of the regulator equals:

IREG(max) = -R----t-h---(-j----a-1-)--5-×---0--(--–-V----PT----a–--m---V-b---R----E---G----)

= 1----0-1--0-5---0-×----–-(--V--T---P-a---m–----b-5----) (mA)

When Tamb = 21 °C and VP = 14 V the maximum output

current equals 140 mA.

handbook, halfpage

VP C1(1)

1 µF

8

1

TDA3668AT

VREG = 5 V

C2 (2)

2, 3, 6, 7

MGS592

(1) C1 is optional (to minimize supply noise only).

(2) C2 ≤ 4700 µF.

Fig.7 Application circuit with backup function.

2000 Feb 01

7

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