Functional Description of the SIM 1-2
SIM 1-2
26
C79000-G8976-C215-01
2.4.3 DC/DC Converters S1 and S2
These outputs are switches for setting up a DC/DC converter. By connecting a
transformer, a push-pull transformer for the power supply of a non-floating load can
be implemented. Two stages of the DC/DC converter start up as soon as a stable
VE supply voltage is present: in other words, before RESET becomes inactive.
To ensure that the VE supply voltage does not break down when the push-pull
transformer is starting up (depending on the backup capacitance C
VE
and the set
bus current), the startup takes several stages. The result of startup depends largely
on the load on the secondary side. It switches to normal operation after 20 ms with
the bridge branches then only functioning as switches. If the voltage at VE sinks
below 80% of its desired value due to the load, the startup is repeated from the
beginning.
The voltage at the open circuit breaker achieves twice the voltage of VE due to
center tapped transformer connected downstream. Moreover, the energy stored in
the leakage inductance of the transformer can induce brief voltage peaks when
switching the transistor bridge (circuit breaker) that are far higher than twice the
value of VE and therefore destroy the circuit breaker. To prevent this, the voltage is
limited internally to approximately 20 V. The ability of this voltage limitation to
absorb is, however, limited to the energy stored in a leakage inductance of 15 µH.
When using a transformer with a leakage inductance of 15 µH to 70 µH, an
additional protective circuit must be use to limit the voltage to 2xVE < U
S1,S2
<< 20
V. A protective circuit between VE and the circuit breakers S1 and S2, each
consisting of BAT45 and BZX84C7V5 connected in series.
●
Transformers with a leakage inductance up to 15 µH can be activated at S1
and S2 without any further protective circuit.
●
Transformers with a leakage inductance up to 70 µH can only be activated at
S1 and S2 with additional protective circuits (see section 4.4, „Circuit
Examples“).
●
Transformers with a leakage inductance > 70 µH cannot be used.
The effective capacitive load on the secondary side during startup (C
DCDC
) should
not exceed 22 µF at I
BUS
= 50
mA
and 4.7 µF at I
BUS
= 8
mA
(see section 2.4.4, "“).
When using the DC/DC converter on S1 and S2. a minimum current I
BUS
≥
8 mA is
recommended.
Summary of Contents for ASIC SIM 1-2
Page 6: ...Preface SIM 1 2 6 C79000 G8976 C215 01 ...
Page 44: ...Technical Specifications SIM 1 2 44 C79000 G8976 C215 01 ...
Page 46: ...Application Examples SIM 1 2 46 C79000 G8976 C215 01 ...
Page 50: ...Application Examples SIM 1 2 50 C79000 G8976 C215 01 Signal Evaluation in the Demodulator ...
Page 58: ...Application Examples SIM 1 2 58 C79000 G8976 C215 01 ...
