MIC2776N-YM5 TR Micrel Inc, MIC2776N-YM5 TR Datasheet - Page 6

• Manufacturer Part Number: MIC2776N-YM5 TR
• Description: IC SUPERVISOR ADJ MCRPWR SOT23-5
• Manufacturer: Micrel Inc
• Type: Simple Reset/Power-On Resetr

Specifications of MIC2776N-YM5 TR

• Number Of Voltages Monitored: 1
• Output: Open Drain or Open Collector
• Reset: Active Low
• Reset Timeout: 140 ms Minimum
• Voltage - Threshold: Adjustable/Selectable
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Number Of Voltage Supervisors: 1
• Monitored Supervisor Voltage: 0.3
• Reset Threshold Voltage (min): 295mV
• Reset Threshold Voltage (max): 305mV
• 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
• Other names: 576-1103-2

Application Information
Programming the Voltage Threshold
Referring to the “Typical Application Circuit”, the voltage
threshold 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 MIC2776 application
in which the MIC2776 is used to monitor the core supply of a
high-performance CPU or DSP. The core supply, V
this example is 1.0V ±5%. The main power rail and I/O volt-
age, V
is powered by V
= 2.375V; the maximum is 2.5V +5% = 2.625V. This is well
within the MIC2776’s power supply range of 1.5V to 5.5V.
Resistors R1 and R2 must be selected to correspond to the
V
voltage is adequate to insure proper operation, i.e., V
≥ (1.0V –5%) = 0.950V. Because there is always 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 potential variation in
the MIC2776’s voltage reference is specified as ±1.5%. The
resistors chosen will have their own tolerance specification.
This example will assume the use of 1% accurate resistors.
The potential worst-case error 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 MIC2776’s very low input bias current.
MIC2776
CORE
V
where V
R2
R1 = R
I/O
TH
supply of 1.0V. The goal is to insure that the core supply
, is 2.5V ±5%. As shown in Figure 1, the MIC2776
=
TOTAL
=
(
R
V
TOTAL
REF
TOTAL
REF
. Imposing this condition on the resistor val-
I/O
V
×
TH
. The minimum value of V
= 0.300V
– R2
(
)
R1 R2
(
V
R2
REF
+
)
)
TOTAL
is 3MΩ.
TH
I/O
expression to
is 2.5V –5%
CORE
IN
). The
TOTAL
CORE
, in
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
specification 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
[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
R1 = 676.3kΩ ≈ 673kΩ
R2 = 323.7kΩ ≈ 324kΩ
V
V
V
V
is given by:
TH
ERROR
ERROR
ERROR
ERROR
=
TH(max)
V
CORE(min)
CORE(min)
= I
= ±1 × 10
= ±2.189 × 10
= ±2.189mV
1.025
IN(max)
REF
= V
IN
CORE
: specified at ±1.5%
= V
is 10nA. (Note that the typical value
CORE(min)
TH
IN
=
-8
× (R1||R2) =
:
1.025
A × 2.189 ×10
. The target threshold voltage will
TH
0.950
results in
-3
+ 2.5% V
V =
= 0.9268V
,
TH
is [V
TH
TOTAL
5
Ω =
= 1.025 V
TH
REF
November 2005
to minimize
and the equa-
tolerance] +
TH
,
CORE