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TDA3661

Very low dropout voltage/quiescent current adjustable voltage regulator

Philips Electronics 

Philips Semiconductors

Very low dropout voltage/quiescent current

adjustable voltage regulator

Preliminary specification

TDA3661

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 a 100 nF MKT capacitor

connected to the output. When the output current is larger

then 200 µA full stability is guaranteed. Because the

thermal influence on the capacitor value is almost zero, the

regulator will remain stable at a temperature of

Tamb = −40 °C.

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 TDA3661 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.6.

EXAMPLE 3

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

independant of:

• The ESR of the electrolytic capacitor

• The value of the electrolytic capacitor

• The output current.

andbook, halfpage

VP C1(1)

1 µF

Application circuits

The maximum output current of the regulator equals:

8

1

TDA3661

5

2, 3, 6, 7

R1

75.1 kΩ

R2

24.9 kΩ

MGS582

VREG

=5V

C2(2)

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

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

When Tamb = 21 °C, VP = 14 V and VREG = 5 V

(k = 4.01929) the maximum output current equals 140 mA.

For successful operation of the IC (maximum output

current capability) special attention has to be given to the

copper area required as heatsink (connected to all

GND pins), the thermal capacity of the heatsink and its

ability to transfer heat to the external environment. It is

possible to reduce the total thermal resistance from

120 to 50 K/W.

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

(2) C2 ≤ 4700 µF.

Fig.6 Application circuit with backup function.

2000 Feb 01

7

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