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TDA3661A

Very low dropout voltage/quiescent current adjustable voltage regulator

Philips Electronics 

Philips Semiconductors

TDA3661

Very low dropout voltage/quiescent current voltage regulator

11.2 Stability

The regulator is stabilized with an external capacitor connected to the output.

For stable operation:

1. The output capacitor ESR should not exceed 22 Ω (worst case)

2. A maximum ESR may be required; see Table 8

3. It is recommended not to use below 1 mA output current because of reduced phase

margin

4. Use electrolytic capacitors for output capacitor values of 1 µF and above.

Table 8: Minimum ESR values required

IREG (mA)

1

C2 = 100 nF

>0Ω

C2 = 1 µF

> 1.5 Ω

5

>0Ω

>0Ω

10

>0Ω

>0Ω

100

>0Ω

>0Ω

C2 = 10 µF

>0Ω

>0Ω

>0Ω

>0Ω

C2 = 100 µF

>0Ω

>0Ω

>0Ω

>0Ω

11.3 Application circuits

The maximum output current of the regulator equals:

I REG(max) = -R---t--h---(--j---–--1-a--5-)--0-×----–-(--V-T---P-a---m-–---b-V-----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 155 K/W to 50 K/W.

11.3.1 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 Figure 3.

9397 750 15049

Product data sheet

Rev. 05 — 28 June 2005

© Koninklijke Philips Electronics N.V. 2005. All rights reserved.

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