AMIS-49200 Datasheet, PDF (14/22 Pages) AMI SEMICONDUCTOR – Fieldbus MAU Chip

AMIS-49200 Fieldbus MAU
Data Sheet
Low Voltage Detectors
VDD
0.9*VREF
SHSETIN
VCC2
C3
R1
N_PFail1
4
C1
VDD
0.9*VREF
SRSETIN
VCC2
C4
N_PFail2
R2
5
C2
Figure 6: Low Voltage Detectors
If you do not use one of the regulators, the corresponding alarm signal can potentially be used to monitor another signal. For example,
if the series regulator is not used, SRAO should be left open, SRTR tied to VCC, VO grounded and SRSET left open. Then SRSETIN
can be the input for monitoring another voltage signal with N_PFAIL2.
4.2.4. Voltage Reference
The voltage reference circuitry generates two voltage signals, VREF and VMID. VREF comes from a bandgap circuit and is used as
the reference voltage for all circuits in AMIS-49200 Fieldbus MAU. The typical value for VREF is 1.181V. VREF also passes through
an analog switch, which is controlled by the test-mux control signals MS0-MS3. When MS0-MS3 are all at GND the analog switch is
closed and VREF is connected to Pin 2. If any of the signals MS0-MS3 are not at GND, the analog switch is open and Pin 2 will be
floating. When the analog switch controlling Pin 2 is closed and VREF is present at Pin 2, no load should be connected to this pin
(internal use only). See Figure 7 for the details.
An operational amplifier is regulating VMID to provide a bias (common) level for the AC signals. Its typical voltage is 2V. A capacitor
larger than 0.01µF is necessary on VMID to remove high-frequency ripple.
To Test Mux
Control Inputs
41 ^MS0
42 ^MS1
43 ^MS2
2 ^VREF
39 ^VSS
Voltage Reference
VCC
VREFBG
Bandgap
Vref=1.185V
(typ)
Tol. = +/- 2%
Bandgap should have its own
ground trace or star connection
to system ground.
Vmid Reference
R
0.688R
237K
163.1K
VCC
VREFBG
A5
Vmid
Figure 7: Bandgap and VMID Voltage Reference
Vmid
3
AMI Semiconductor – Jan. 07, M-20532-003
14
www.amis.com