ADM1068 데이터 시트보기 (PDF) - Analog Devices
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ADM1068 Datasheet PDF : 25 Pages
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Data Sheet
ADM1068
INPUTS
SUPPLY SUPERVISION
The threshold value required is given by
The ADM1068 has eight programmable inputs. Four of these are
dedicated supply fault detectors (SFDs). These dedicated inputs
are called VH and VPx (VP1 to VP3) by default. The other four
inputs are labeled VXx (VX1 to VX4) and have dual functionality.
They can be used either as SFDs, with functionality similar to the
VH and VPx, or as CMOS-/TTL-compatible logic inputs to the
device. Therefore, the ADM1068 can have up to eight analog
inputs, a minimum of four analog inputs and four digital inputs,
or a combination thereof. If an input is used as an analog input,
it cannot be used as a digital input. Therefore, a configuration
requiring eight analog inputs has no available digital inputs.
Table 6 shows the details of each input.
PROGRAMMING THE SUPPLY FAULT DETECTORS
The ADM1068 can have up to eight SFDs on its eight input
channels. These highly programmable reset generators enable the
supervision of up to eight supply voltages. The supplies can be as
low as 0.573 V and as high as 14.4 V. The inputs can be configured
to detect an undervoltage fault (the input voltage drops below a
preprogrammed value), an overvoltage fault (the input voltage
rises above a preprogrammed value), or an out-of-window fault
(the input voltage is outside a preprogrammed range). The thresh-
olds can be programmed to an 8-bit resolution in registers provided
in the ADM1068. This translates to a voltage resolution that is
dependent on the range selected.
The resolution is given by
Step Size = Threshold Range/255
Therefore, if the high range is selected on VH, the step size can
be calculated as follows:
VT = (VR × N)/255 + VB
where:
VT is the desired threshold voltage (undervoltage or overvoltage).
VR is the voltage range.
N is the decimal value of the 8-bit code.
VB is the bottom of the range.
Reversing the equation, the code for a desired threshold is given by
N = 255 × (VT − VB)/VR
For example, if the user wants to set a 5 V overvoltage threshold
on VP1, the code to be programmed in the PS1OVTH register
(as discussed in the AN-721 Application Note) is given by
N = 255 × (5 − 2.5)/3.5
Therefore, N = 182 (1011 0110 or 0xB6).
INPUT COMPARATOR HYSTERESIS
The UV and OV comparators shown in Figure 15 are always
monitoring VPx. To avoid chatter (multiple transitions when the
input is very close to the set threshold level), these comparators
have digitally programmable hysteresis. The hysteresis can be
programmed up to the values shown in Table 6.
ULTRA
LOW
VPx
RANGE
SELECT
OV
+ COMPARATOR
VREF
–
GLITCH
FILTER
FAULT
OUTPUT
LOW
MID
+
–
UV
FAULT TYPE
COMPARATOR SELECT
(14.4 V − 6.0 V)/255 = 32.9 mV
Table 5 lists the upper and lower limits of each available range,
the bottom of each range (VB), and the range itself (VR).
Table 5. Voltage Range Limits
Voltage Range (V)
0.573 to 1.375
1.25 to 3.00
2.5 to 6.0
6.0 to 14.4
VB (V)
0.573
1.25
2.5
6.0
VR (V)
0.802
1.75
3.5
8.4
Figure 15. Supply Fault Detector Block
The hysteresis is added after a supply voltage goes out of
tolerance. Therefore, the user can program the amount above
the undervoltage threshold to which the input must rise before
an undervoltage fault is deasserted. Similarly, the user can program
the amount below the overvoltage threshold to which an input
must fall before an overvoltage fault is deasserted.
Table 6. Input Functions, Thresholds, and Ranges
Input Function
Voltage Range (V)
VH High Voltage Analog Input 2.5 to 6.0
6.0 to 14.4
VPx Positive Analog Input
0.573 to 1.375
1.25 to 3.00
2.5 to 6.0
VXx High-Z Analog Input
0.573 to 1.375
Digital Input
0 to 5.0
Maximum Hysteresis
425 mV
1.02 V
97.5 mV
212 mV
425 mV
97.5 mV
Not Applicable
Voltage Resolution (mV)
13.7
32.9
3.14
6.8
13.7
3.14
Not Applicable
Glitch Filter (μs)
0 to 100
0 to 100
0 to 100
0 to 100
0 to 100
0 to 100
0 to 100
Rev. D | Page 11 of 25
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