User Manual
GAMMA instabus
Release: February 2012
KNX EIB TP-UART 2-IC
Siemens AG pages 42 Technical Manual
Infrastructure and Cities Sector,
Building Technologies
Control Products and Systems © Siemens AG 2012 page 13
P. O. Box 10 09 53, Subject to change without further notice.
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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
V20
) shall have a fallback characteristic in order
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
LL
=
V
V20(min)
/ I
V20
.
Symbol Parameter Min Max Unit
Note
V
V20
supply voltage (when current limit is not active) 17.5 22.5 V 1)
C
V20
external storage capacitance 8 1200 µF 6)
C
V20
external storage capacitance when V20PD is active 0 µF
I
V20
Load current with current limiting not active 25 mA 2)
I
V20_ILIM
Load current with current limiting active 30 mA 3)
I
V20_SHORT
Load current under short circuit conditions 5 16 mA 4)
R
LL
Resistive Load Line 700 8)
1) V
VSP
≥ V
V20
+ V
DROP
; for static load currents in the range defined by I
V20
; V
DROP
≤ 1V
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
Table 11 Supply Pin V20
Symbol
Parameter R20 Unit IV20
1
Unit R
LL
Unit
262 k 5 mA 3500
345 k 10 mA 1750
520 k 15 mA 1167
1000 k 20 mA 875
R20 External maximum current setting
resistance
o/c k 25 mA 700
Table 12 External maximum current setting resistance