AMIS-49200 Fieldbus MAU
4.0 Theory of Operation
4.1 Overview
Data Sheet
AMIS-49200 incorporates two different power supply circuits. Both derive their power from the bus. Using the internal configuration,
the shunt regulator is set for 5V and the series regulator is set for 3V. Users can modify either power supply by adding external
components. AMIS-49200 Fieldbus can also monitor these power supply voltages and generate power-fail signals if they fall below a
specified value.
AMIS-49200 Fieldbus MAU transmits a Manchester-encoded signal provided from a standard MDS-MAU interface. The output driver
makes it possible to design various signal circuits, which depend on the power requirements of your device. The slew rate of the signal
can be controlled to minimize unnecessary radiation as specified in IEC/ISA standards.
AMIS-49200 Fieldbus MAU has a built-in band-pass filter which makes it easy to design your own receiver. The receive block operates
on a Manchester-encoded signal. It decodes the signal and verifies proper amplitude with a zero-cross and carrier detect circuit,
respectively. Detected signals are then passed on to a controller with the standard MDS-MAU interface.
4.2 Power Supply Block
The power supply block contains four sub-blocks:
1.
2.
3.
4.
A shunt regulator - for establishing a supply voltage of V
CC
(typ. = 5V) used by the analog circuitry
A series regulator - for establishing a supply voltage of V
DD
(typ. = 3V) used for digital circuitry
Two low voltage detectors - for monitoring the two supply voltages
A bandgap voltage reference - which is used internally for generating a bias level for AC signals
4.2.1. Shunt Regulator
The shunt regulator controls its sink current to the SHUNT pin so that the voltage applied to the SHSETIN pin is equal to V
REF
. The V
CC
input is divided by an internal network to provide a voltage equal to Vref at the SHSET pin. If SHSET and SHSETIN pins are tied
together, and V
CC
and SHUNT pins are connected to a power source of high impedance (e.g., current mirror circuit of signal driver), the
Shunt regulator provides 5V power to itself and external circuits. A capacitor of 5µF or larger capacity is necessary to stabilize this
regulator.
It is possible to increase the V
CC
voltage up to 6.2V by dividing V
CC
with an external network to supply the appropriate voltage to
SHSETIN pin. In this case, SHSET pin must be kept open. The output voltage is determined by the following equation:
V
CC
= V
REF
×
(1 + R
1
/ R
2
)
Shunt Regulator
(Internal Configuration
)
VCC
System
VCC
Shunt Regulator
(External Configuration
)
VCC
System
VCC
18
3.25Rsh
16Meg
VREF
Rsh
A6
Cfb
50pF
25mA
(Max)
SHUNT
3.25Rsh
16Meg
VREF
Rsh
A6
Cfb
50pF
25mA
(Max)
18
R1
SHUNT
8
8
R2
7
SHSET
6
SHSETIN
9
SGND
7
N/C
SHSET
6
SHSETIN
9
SGND
Figure 4: Shunt Regulator
AMI Semiconductor
– Jan. 07, M-20532-003
www.amis.com
12
AMI [ AMI SEMICONDUCTOR ]
