TH8065 datasheet(28/40 Pages) MELEXIS

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TH8065

Voltage Regulator with LIN Transceiver and Watchdog

TH8065 – Datasheet

Page 28 of 40

3901008065

May 2006

Rev 003

Load Capacitor on VCC CL

The regulator is stabilized by the output capacitor CL. The TH8065 requires a minimum of 4.7µF capacitor

connected to the 5V output to insure stability. This capacitor should maintain its ESR in the stable region of

the ESR curve (See Figure 20) over the full operating temperature range of the application. It has to be taken

into account that the capacitance value and the ESR of a capacitor changes with temperature. The minimal

capacitance value must also be kept within the whole operating temperature range.

0,01

0,1

100

1020

4050

load current [mA]

Figure 20 - ESR Curves for 6.8

μF ≤ CL ≤ 100μF and Frequency of 100 kHz

The value and type of the output capacitor can be selected using the diagram shown in Figure 20. The load

capacitor should be placed as close as possible (< 1cm) to the VCC pin.

Capacitance Value

The capacitance value of an electrolytic capacitor is dependent from the voltage, temperature and the

frequency. The temperature coefficient of the capacitor value is positive, that means that the value increases

with increasing of the temperature. The capacitance value decreases with increasing of the frequency. This

behaviour of a capacitor can cause that at TA=-40°C the capacitance value falls below the minimum required

capacitance for the regulator. In this case the regulator becomes instable, which means the regulator starts

oscillation. The nominal value of the capacitor at TA=25°C has to be chosen with enough margin under

consideration of the capacitor specification. The instable behaviour will be amplified because of the

decreasing of the capacitance with this oscillation.

ESR

The equivalent serial resistance is the resistor part of the equivalent circuit diagram of a capacitor. The ESR

value is dependent from the temperature and frequency. Normally the specified ESR values for a capacitor is

valid at a temperature of TA=25°C and a frequency of f=100 kHz.

The temperature coefficient is negative, which means with increasing of the temperature the ESR value

decreases. In the choice of the capacitance has to be taken into account that the ESR can decrease at TA=-

40°C dramatically that the valid operating area can be left, which causes that the regulator will be instable.

Stable Area

TH8065 Datasheet(PDF) 28 Page - Melexis Microelectronic Systems