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KNX EIB TP-UART 2-IC
2.2.9 Supply Pin V20 and Pin R20
Pin V20 delivers the internally generated supply voltage to external loads. The supply is generated by a
series regulator. Internal input voltage for V20 is VDDH. The V20 regulator is switched off during
softstart, making V20 unavailable
An external short-circuit from the V20 pin to VB- will not cause a destruction of the ASIC, interference
on the bus or disturb generation of VCC. Relation V20(I
to limit the power loss.
The maximum current available from the V20 regulator can be reduced by adding an external
resistance connected between the R20 pin and VB-. The R20 pin can be left open circuit if no
reduction in maximum current is required.
In an applications where the V20 regulator is not going to be used pin 25 V20PD can be used to
disable the V20 regulator. The pin should be hard wired to VB- for normal V20 operation and hard
wired to VDP to disable the V20 regulator. The pin should not be used to dynamically control the state
of the V20 regulator when the device is powered up. The CV20 capacitor can be removed from the
application when V20PD is active (hard wired to VDP)
The IV characteristic of the regulated voltage should not cross the resistive load line defined by R
V
/ I
.
V20(min)
V20
Symbol
Parameter
V
supply voltage (when current limit is not active)
V20
C
external storage capacitance
V20
C
external storage capacitance when V20PD is active
V20
I
Load current with current limiting not active
V20
I
Load current with current limiting active
V20_ILIM
I
Load current under short circuit conditions
V20_SHORT
R
Resistive Load Line
LL
1) V
≥ V
+ V
VSP
V20
2) maximum allowed load at V20 for full output voltage.
3) current limitation of fallback characteristic
4) in case of short circuit: V20 connected with VB-, VB+=30V, VSP = 29.5V
5) power limitation of fallback characteristic
6) In parallel with ceramic 100nF
7) External resistor tolerance of ±1%
8) See Table 12 External maximum current setting resistance
Symbol Parameter
R20
External maximum current setting
resistance
Siemens AG
Infrastructure and Cities Sector,
Building Technologies
Control Products and Systems
P. O. Box 10 09 53,
D-93009 Regensburg
; for static load currents in the range defined by I
DROP
Table 11 Supply Pin V20
Table 12 External maximum current setting resistance
Subject to change without further notice.
) shall have a fallback characteristic in order
V20
R20
Unit
262
k
345
k
520
k
1000
k
o/c
k
pages 42
© Siemens AG 2012
GAMMA instabus
Release: February 2012
Min
Max
Unit
17.5
22.5
V
8
1200
µF
0
µF
25
mA
30
mA
5
16
mA
700
; V
≤ 1V
V20
DROP
1
IV20
Unit
R
LL
5
mA
3500
10
mA
1750
15
mA
1167
20
mA
875
25
mA
700
Technical Manual
=
LL
Note
1)
6)
2)
3)
4)
8)
Unit
page 13
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