TH8065 Datasheet, PDF (27/40 Pages) Melexis Microelectronic Systems – Voltage Regulator with LIN Transceiver and Watchdog

TH8065
Voltage Regulator with LIN Transceiver and Watchdog
80
maximum current
70
T_A=85°C
60
50
T_A=125°C
40
30
20
10
0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
V_SUP [V]
Figure 19 - Save operating area
The linear regulator of the TH8065 operates with input voltages up to 18V and can output a current of 70mA.
The maximum power dissipation limits the maximum output current at high input voltages and high ambient
temperatures. The output current of 70mA at an ambient temperature of T_A = 125°C is only possible with
small voltage differences between V_SUP and V_CC. See Figure 19 for safe operating areas for different ambient
temperatures. The TH8065 is able to output 70mA over the whole voltage range if the max ambient
temperature is limited to 85°C.
4.2 Low Dropout Regulator
The voltage regulator of theTH8065 is a low dropout regulator (LDO) with a p-MOSFET as driving transistor.
This kind of regulator has a standard pole, generated from the internal frequency compensation and an
additional pole, which is dependent from the load and the load capacitance. This additional pole can cause
an instable behaviour of the regulator! It is required a zero point to compensate this additional pole. It can be
realised via an additional load resistor in series with a load capacitor. It is used for this compensation the
equivalent series resistance (ESR) of the load capacitor. Every real capacitor is characterized with an ESR
value. With the help of this ESR value an additional zero point is implemented into the amplification loop and
therefore the result of the negative phase shift is compensated.
Because of this correlation the regulator has a stable operating area which is defined by the load resistance
R_L, the load capacitor C_L and the corresponding ESR value. The load resistance resp. load current is defined
by the application itself and therefore the compensation of the pole can only be done via variation of the load
capacitance and ESR value.
Input Capacitor on VSUP C_IN
An input capacitance is necessary of C_IN ≥ 4.7µF. Higher capacitance values improves the line transient
response and the supply noise rejection behaviour. The combination of electrolytic capacitor (e.g.100µF) in
parallel with a ceramic RF-capacitor (e.g.100nF) archives good disturbance suppressing.
The input capacitor should be placed as close as possible (< 1cm) to the VSUP pin.
TH8065 – Datasheet
3901008065
Page 27 of 40
May 2006
Rev 003