TH8065 Datasheet, PDF (28/40 Pages) Melexis Microelectronic Systems – Voltage Regulator with LIN Transceiver and Watchdog

TH8065
Voltage Regulator with LIN Transceiver and Watchdog
Load Capacitor on VCC C_L
The regulator is stabilized by the output capacitor C_L. 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.
100
10
1
Stable Area
0,1
0,01
0
10
20
30
40
50
load current [mA]
Figure 20 - ESR Curves for 6.8μF ≤ C_L ≤ 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 T_A=-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 T_A=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 T_A=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 T_A=-
40°C dramatically that the valid operating area can be left, which causes that the regulator will be instable.
TH8065 – Datasheet
3901008065
Page 28 of 40
May 2006
Rev 003