MIC2774N-29YM5 TR Micrel Inc, MIC2774N-29YM5 TR Datasheet - Page 6

• Manufacturer Part Number: MIC2774N-29YM5 TR
• Description: Dual Ultra-Low-V Supervisor
• Manufacturer: Micrel Inc
• Type: Multi-Voltage Supervisorr

Specifications of MIC2774N-29YM5 TR

• Open-drain: Manual Reset, SOT23-9 -
• Number Of Voltages Monitored: 2
• Output: Open Drain or Open Collector
• Reset: Active Low
• Reset Timeout: 140 ms Minimum
• Voltage - Threshold: 2.93V, Adj
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Voltage Supervisor Type: Voltage Monitor
• Number Of Voltage Supervisors: 1
• Monitored Supervisor Voltage: 2.93
• Reset Threshold Voltage (min): 2.886V
• Operating Supply Voltage (min): 1.5V
• Operating Supply Voltage (max): 5.5V
• Package Type: SOT-23
• Operating Temperature Classification: Industrial
• Operating Temp Range: -40C to 85C
• Pin Count: 5
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Compliant, Lead free / RoHS Compliant
• Other names: 576-1101-2

Application Information
Programming the Voltage Threshold
Referring to the “Typical Application Circuit”, the voltage
threshold on the IN pin is calculated as follows:
In order to provide the additional criteria needed to solve
for the resistor values, the resistors can be selected such
that the two resistors have a given total value, that is, R1
+ R2 = R
ues provides two equations that can be solved for the two
unknown resistor values. A value such as 1MΩ for R
is a reasonable choice since it keeps quiescent current to a
generally acceptable level while not causing any measurable
errors due to input bias currents. The larger the resistors, the
larger the potential errors due to input bias current (I
maximum recommended value of R
Applying this criteria and rearranging the V
solve for the resistor values gives:
Application Example
Figure 1 below illustrates a hypothetical MIC2774L-23 ap-
plication in which the MIC2774L-23 is used to monitor the
core and I/O supplies of a high-performance CPU or DSP.
The core supply, V
main power rail and I/O voltage, V
in Figure 1, the MIC2774 is powered by V
value of V
+5% = 2.625V. This is well within the device’s supply range
of 1.5V to 5.5V.
Resistors R1 and R2 must be selected to correspond to the
V
supply voltage is adequate to insure proper operation, i.e.,
V
a small degree of uncertainty due to the accuracy of the
resistors, variations in the devices’ voltage reference, etc.,
the threshold will be set slightly below this value. The po-
tential variation in the MIC2774’s voltage reference (V
is specifi ed as ±1.5%. The resistors chosen will have their
own tolerance specifi cation. This example will assume the
use of 1% accurate resistors. The potential worst-case er-
ror contribution due to input bias current can be calculated
once the resistor values are chosen. If the guidelines above
regarding the maximum total value of R1+R2 are followed, this
error contribution will be very small thanks to the MIC2774’s
very low input bias current.
M9999-102605
CORE
CORE
V
V
V
V
V
where V
R2
R1
TH
TH
supply of 1.0V. The goal is to insure that the core
≥ (1.0V –5%) = 0.950V. Because there is always
=
=
=
=
TOTAL
=
=
=
I/O
R
R
R
R
R
R
R
R
R
(
(
(
(
(
(
(
(
R
R
R
R
R
R
R
R
R
R
R
R
V
V
V
V
V
TOTAL
TOTAL
TOTAL
TOTAL
REF
REF
REF
TOTAL
TOTAL
TOTAL
TOTAL
is 2.5V –5% = 2.375V; the maximum is 2.5V
REF
. Imposing this condition on the resistor val-
V
×
×
×
TH
= 0.300V
−
−
−
CORE
(
(
(
(
)
)
)
)
)
)
)
)
R1
R1 R2
(
(
(
(
(
R2
R
R
R
R
R
R
R
R
V
V
V
V
V
V
V
V
V
V
V
V
R2
REF
REF
+
+
, in the example is 1.0V ±5%. The
R2
)
)
)
)
)
)
)
)
)
I/O
TOTAL
TOTAL
TOTAL
, is 2.5V ±5%. As shown
I/O
is 3MΩ.
is 3MΩ.
TH
. The minimum
expression to
IN
). The
TOTAL
REF
)
6
To summarize, the various potential error sources are:
Taking the various potential error sources into account, the
threshold voltage will be set slightly below the minimum V
specifi cation of 0.950V so that when the actual threshold
voltage is at its maximum, it will not intrude into the normal
operating range of V
be set as follows:
Given that the total tolerance on V
tolerance] + [resistor tolerance]
therefore, solving for V
Solving for R1 and R2 using this value for V
tions above yields:
The resulting circuit is shown in Figure 1.
Input Bias Current Effects
Now that the resistor values are known, it is possible to cal-
culate the maximum potential error due to input bias current,
I
maximum value of I
is a much smaller 5pA!) The magnitude of the offset caused
by I
The typical error is about three orders of magnitude lower
than this - close to one microvolt! Generally, the error
due to input bias can be discounted. If it is to be taken
into account, simply adjust the target threshold voltage
downward by this amount and recalculate R1 and R2. The
resulting value will be very close to optimum. If accuracy
is more important than the quiescent current in the
resistors, simply reduce the value of R
offset errors.
IN
• Variation in V
• Resistor tolerance:
• Input bias current, I
. As shown in the “Electrical Characteristics” table, the
IN
chosen by designer (typically ≤ ±1%)
calculated once resistor values are known, typically
very small
= ±1.5% + ±1% = ±2.5%,
and V
then V
V
V
V
R1 = 676.3kΩ ≈ 673kΩ
R2 = 323.7kΩ ≈ 324kΩ
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
is given by:
ERROR
ERROR
ERROR
ERROR
TH
TH
ERROR
ERROR
ERROR
ERROR
=
=
=
TH(max)
V
CORE(min)
CORE(min)
= ±
=
I =
=
= ±
= ±
1.025
I
I
I
I
IN(max)
IN(max)
IN(max)
REF
2.189mV
2
2
2
2
1 10
1
1
1
1×
2.189 10
2
2
2
2
×
×
×
×
= V
IN
10
10
CORE
: specifi ed at ±1.5%
= V
is 10nA. (Note that the typical value
−8
CORE(min)
TH
IN
×
×
×
×
=
8
A 2.189 10
A 2
A 2
:
(
(
(
(
1.025
. The target threshold voltage will
TH
0.950
results in
R1
R1 ||
×
×
×
×
×
−
3
+ 2.5% V
|| R2
V =
R2 =
= 0.9268V
,
)
)
)
)
TH
×
for the IN pin is [V
TH
TOTAL
TOTAL
TOTAL
5
Ω
= 1.025 V
=
TH
to minimize
to minimize
and the equa-
October 2005
TH
,
CORE
REF