Datasheet

9397 750 15049 © Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Product data sheet Rev. 05 — 28 June 2005 5 of 16
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.
11.3 Application circuits
The maximum output current of the regulator equals:
When T
amb
=21°C, V
P
=14VandV
REG
= 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.
Table 8: Minimum ESR values required
I
REG
(mA) C2 = 100 nF C2 = 1 µF C2 = 10 µF C2 = 100 µF
1 > 0 Ω> 1.5 Ω> 0 Ω> 0 Ω
5 > 0 Ω> 0 Ω> 0 Ω> 0 Ω
10 > 0 Ω> 0 Ω> 0 Ω> 0 Ω
100 > 0 Ω> 0 Ω> 0 Ω> 0 Ω
I
REG max()
150 T
amb
–
R
th j a–()
V
P
V
REG
–()×
-----------------------------------------------------------
150 T
amb
–
100 V
P
5–()×
------------------------------------
mA()==