
NCV7361A
http://onsemi.com
23
Capacity Value
The capacity value of an electrolytic capacitor is
dependence from the voltage, temperature and the
frequency. The temperature coefficient of the capacity
value is positive, that means that the value increases with
increasing of the temperature. The capacity value
decreases with increasing of the frequency. This behavior
of a capacitor can cause that at T
A
= 40
°
C the capacity
value falls below the minimum required capacity 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 behavior will be amplified
because of the decreasing of the capacity 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 capacity 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.
Tantalum Capacitors
This type of capacitor has a low dependence of the
capacity and the ESR from the temperature and is therefore
well suitable as V
OUT
load capacity.
Aluminum Capacitors
These capacitors show a strong influence of the capacity
and the ESR from the temperature. These characteristic
restrains the usability as load capacity for the low drop
regulator of NCV7361A.
Figure 36. Application Circuit (Slave Node)
V
SUP
EN
NCV7361A
GND
BUS
V
OUT
RESET
TxD
RxD
+
220 pF
100 nF
100 F
Reverse
ProtectionDiode
V
BAT
LINBUS
+
100 nF
10 F...100 F
+5 V
C
100 p
RCFilter
10
82p
LCFilter
33 H
or
Optional
EMI Suppressing
To minimize the influence of EMI from the bus line, a
220 pF capacitor should be directly connected to the BUS
pin (see Figure 36).
The value of the filter capacity can be adjusted to the size
of the LIN network. 220 pF should be used for bigger
networks. Values from 333 pF up to 1.0 nF should be used
for middle to small LIN networks. Finally the size of the
filter capacitor influences the effectiveness of the EMI
suppressing in conformance to the maximum LIN bus
capacity of 10 nF.
LCfilters or RCfilters can also be used. The value of
C, L or R, depends on the corner frequency, the maximum
LIN bus capacity (10 nF) and the compliance with the DC
and AC LIN bus parameters.