ADM1186(Rev0) データシートの表示（PDF） - Analog Devices
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ADM1186
(Rev.:Rev0)
(Rev.:Rev0)
Analog Devices
ADM1186 Datasheet PDF : 28 Pages
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ADM1186
SEQUENCE CONTROL USING A SUPPLY RAIL
The UP and DOWN inputs on the ADM1186-1 and the
UP/DOWN input on the ADM1186-2 are used to initiate
power-up and power-down sequences. These inputs are
designed for use with digital or analog signals, such as power
supply rails. Using a power supply rail to control the up and
down sequencing allows the ADM1186 to perform sequencing
and monitoring functions for five supply rails.
When using a supply rail to control an ADM1186-1 (with
the UP and DOWN pins connected) or an ADM1186-2,
some hysteresis is required. The hysteresis is added on the
joined UP and DOWN pins of the ADM1186-1 or on the
UP/DOWN pin of the ADM1186-2 to ensure that a slowly
ramping supply rail does not cause spurious rising or falling
edges that would otherwise cause state machine faults.
To provide the necessary hysteresis, a single additional resistor
(RH in Figure 27) is connected between the joined UP and
DOWN pins of the ADM1186-1 and the OUT1 pin of the
device, or between the UP/DOWN pin of the ADM1186-2 and
the OUT1 pin of the device.
RH
VIN
3.3V
VP
R1
ADM1186-1 VCC
RP
UP
+
OUT1
–
R2
STATE
DOWN
+
MACHINE
–
1.4V
Figure 27. Using a Supply Rail to Control Sequencing with Hysteresis
When OUT1 is low, the resistor RH sinks current from the
node at the midpoint of R1 and R2, slightly increasing the VIN
voltage needed to start a power-up sequence, referred to as VH.
When OUT1 is high, RH sources current into the midpoint of
R1 and R2, decreasing the VIN voltage necessary to start a
power-down sequence, referred to as VL.
The hysteresis at the VIN node is simply VH − VL. As the R1
and R2 resistors scale VIN down, the hysteresis on VIN is also
scaled down. The scaled hysteresis, VSHYS, at the inputs to the
UP and DOWN pins (ADM1186-1) or the UP/DOWN pin
(ADM1186-2) must be at least 75 mV. The value of RH is
selected to ensure that this is the case.
VH
= 1.4 × ⎢⎣⎡1 + ⎜⎝⎛ R1×
R2 + RH
R2 × RH
⎟⎠⎞⎥⎦⎤
VL
=
1.4
+
⎡
⎢R1
⎢⎣
×
⎜⎛
⎜⎝
1.4
R2
−
VP
RH
− 1.4
+ RP
⎟⎟⎠⎞⎥⎥⎦⎤
VSHYS
= (VH
−VL ) ×
⎜⎝⎛
R2
R1 + R2
⎟⎠⎞
In the example application shown in Figure 27, the following
values could be used:
RP = 10 kΩ
VP = 5 V
VIN = 3.3 V
The values of the R1 and R2 resistors determine the midpoint
of the hysteresis, VMID, about which VH and VL set the levels at
which power-up and power-down sequences are initiated. For a
3.3 V supply, a threshold just below 3 V could be used, making
R1 = 11 kΩ and R2 = 10 kΩ and giving a midpoint of 2.94 V.
V MID
=
VIN × R2
R1+ R2
=
3.3×10 k
11 k+10 k
VMID = 2.94 V
As a general rule, the value for RH is approximately 60 times
the value of R1 in parallel with R2. In this example, R1 in
parallel with R2 is 5.24 kΩ, so RH would be approximately
314 kΩ. Taking a value of 300 kΩ for RH and using this value
in the previous equations for VH, VL, and VSHYS, the following
values are obtained:
VH
=
1.4
×
⎡
⎢⎣1
+
⎜⎛11 k
⎝
×
10 k
10 k
+
×
300
300
k
k
⎟⎠⎞⎥⎦⎤
VH = 2.991 V
VL
⎡
= 1.4 + ⎢11k
⎢⎣
×
⎜⎛
⎜⎝
1.4
10 k
−
5
300
−
k
1.4
+10
k
⎟⎟⎠⎞⎥⎥⎦⎤
VL = 2.812 V
V SHYS
=
(2.991
−
2.812)
×
⎜⎛
⎝
11
10
k+
k
10
k
⎟⎞
⎠
VSHYS = 0.085 V
Because the value of VSHYS is greater than the 75 mV of scaled
hysteresis required, the RH resistor value selected is sufficient.
If the value of VSHYS obtained is too small, the value of RH can
be reduced, increasing the scaled hysteresis provided.
It should be noted that it is not possible to directly connect the
VCC supply to the UP pin (ADM1186-1) or to the UP/DOWN
pin (ADM1186-2) to start a sequence as the VCC comes up.
When the UVLO circuit enables the state machine, it begins
in the fault handler states. To reach the WAIT START state so
that sequencing can begin, the UP pin (ADM1186-1) or the
UP/DOWN pin (ADM1186-2) must be held low after the state
machine is enabled.
Rev. 0 | Page 16 of 28
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