September 29, 2000
1
MIC2774
MIC2774
Micrel
MIC2774
Dual Micro-Power Low Voltage Supervisor
Advance Information
General Description
The MIC2774 is a dual power supply supervisor that provides
under-voltage monitoring, manual reset capability, and power-
on reset generation in a compact 5-pin SOT package. Fea-
tures include two under-voltage detectors, one fixed and one
adjustable, and a choice of reset outputs. One under-voltage
detector compares V
DD
against a fixed threshold. Ten fac-
tory-programmed thresholds are available. The second, user-
adjustable input is compared against a 300mV reference.
This low reference voltage allows monitoring voltages lower
than those supported by previous supervisor ICs.
The reset outputs are asserted at power-on and any time
either voltage drops below the programmed threshold volt-
ages and remains asserted for 140ms (min.) after they
subsequently rise back above the threshold boundaries.
Manual reset functionality can be provided by a switch
connected between ground and the /MR input. A wide choice
of voltage thresholds provides for a variety of supply voltages
and tolerances. Hysteresis is included to prevent chattering
due to noise. Typical supply current is a low 3.5
A.
Typical Application
IN
/RST
VDD
/MR
GND
MIC2774L-23
R1
R2
/RESET
VCORE
GND
Power_Good
V
CORE
1.0V
Manual
Reset
MICROPROCESSOR
VI/O
V
I/O
2.5V
Features
Monitors two independent power supplies for under-
voltage conditions
One fixed and one user adjustable input
Choice of factory-programmed thresholds
Adjustable input can monitor supplies as low as 0.3V
Generates 140ms (minimum) power-on reset pulse
Manual reset input
Choice of active-high, active-low, or open-drain active-
low reset outputs
Inputs may be pulled above V
DD
(7V abs. max.)
Open-drain output can be pulled above V
DD
(7V abs
max.)
/RST output valid down to 1.2V
Ultra-low supply current, 3.5
A typical
Rejects brief input transients
IttyBittyTM 5-lead SOT-23 package
Pin compatible upgrade for MAX6306/09/12
Applications
Monitoring processor ASIC, or FAGA core and I/O
voltages
PDAs, hand-held PCs
Embedded controllers
Telecommunications systems
Power supplies
Wireless / Cellular systems
Networking hardware
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 http://www.micrel.com
IttyBittyTM is a trademark of Micrel, Inc.
Ordering Information
Part Number
Marking
Reset Output
Temperature Range
Package
MIC2774N-XXBM5
UGXX
Open-Drain, Active-Low (/RST)
40
C to +85C
SOT-23-5
MIC2774H-XXBM5
UHXX
Active-High, Complementary (RST)
40
C to +85C
SOT-23-5
MIC2774L-XXBM5
UIXX
Active-Low, Complementary (/RST)
40
C to +85C
SOT-23-5
MIC2774
Micrel
MIC2774
2
September 29, 2000
Pin Configuration
RST
VDD
IN
/MR
1
3
4
5
2
GND
SOT-23-5 (M5)
"H" Version
/RST
VDD
IN
/MR
1
3
4
5
2
GND
SOT-23-5 (M5)
"L" and "N" Version
Standard Voltage Options*
Voltage
Typical
Nominal Threshold
Code
Application (V
DD
)
Voltage (V
TH
)
46
5.0V
5%
4.68
44
5.0V
10%
4.43
31
3.3V
5%
3.09
29
3.3V
10%
2.93
28
3.0V
5%
2.81
26
2.85V
5%
2.67
25
2.70V
5%
2.53
23
2.5V
5%
2.34
22
2.4V
5%
2.25
17
1.8V
5%
1.69
*There are ten standard versions available with an order increment of 3000 pieces. Samples of standard versions are
normally available from stock. Contact factory for information on non-standard versions. Available in tape-and-reel only.
Pin Description
Pin Number
Pin Number
Pin Name
Pin Function
MIC2774H
MIC2774L
MIC2774N
1
RST
Digital (Output): Asserted high whenever V
IN
or V
DD
falls below the thresh-
old voltage. It will remain asserted for no less than 140ms after V
IN
and V
DD
return above the threshold limits.
1
/RST
Digital (Output): Asserted low whenever V
IN
or V
DD
falls below the threshold
voltage. It will remain asserted for no less than 140ms after V
IN
and V
DD
return above the threshold limits. (open-drain for "N" version)
2
2
GND
Ground
3
3
/MR
Digital (Input): Driving this pin low initiates immediate and unconditional
reset. Assuming V
IN
and V
DD
are above the thresholds when /MR is
released (returns high), the reset output will be de-asserted no less than
140ms later. /MR may be driven by a logic signal or a mechanical switch.
/MR has an internal pull-up to V
DD
and may be left open if unused.
4
4
IN
Analog (Input): The voltage on this pin is compared to the internal 300mV
reference. An under-voltage condition will trigger a reset sequence.
5
5
VDD
Analog (Input): Power supply input for internal circuitry and input to the fixed
voltage monitor. The voltage on this pin is compared against the internal
reference. An undervoltage condition will trigger a reset sequence.
September 29, 2000
3
MIC2774
MIC2774
Micrel
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
DD
) ..................................... 0.3V to +7V
Input Voltages (V
IN
, V
/MR
) .............................. 0.3V to +7V
Output Voltages (V
/RST
, V
RST
) ....................... 0.3V to +7V
RST, (/RST) Current .................................................. 20mA
Storage Temperature (T
S
) ....................... 65
C to +150C
ESD Rating, Note 3 ................................................... 1.5kV
Operating Ratings
(Note 2)
Supply Voltage (V
DD
) .................................. +1.5V to +5.5V
Input Voltages (V
IN
, V
/MR
) ........................... 0.3V to +6.0V
Output Voltages
V
/RST
(N version), .................................... 0.3V to +6.0V
V
/RST
, V
RST
(H and L versions) ......... 0.3V to V
DD
+0.3V
Ambient Temperature Range (T
A
) ............. 40
C to +85C
Package Thermal Resistance (
JA
) ...................... 256
C/W
Electrical Characteristics
Note 5; T
A
= +25
C, bold values indicate 40C T
A
+85C; unless noted
Symbol
Parameter
Condition
Min
Typ
Max
Units
I
DD
Supply Current
V
DD
= V
IN
= V
TH
+1.6%,
3.5
A
Note 5; /MR, RST, /RST open
VDD VOLTAGE THRESHOLD
Under-Voltage Threshold On V
DD
V
TH
1.5%
V
TH
V
TH
+1.5%
V
(See Standard Voltage Options Table)
V
HYST
Hysteresis Voltage
1
%
IN, UNDER-VOLTAGE DETECTOR INPUT
V
REF
Under-Voltage Threshold
Note 5
295
300
305
mV
V
HYST
Hysteresis Voltage
3
mV
I
IN
Input Current
5
pA
T
MIN
T
A
T
MAX
10
nA
RST, /RST OUTPUTS
t
PROP
Propagation Delay
V
IN
= (V
REF(MAX)
+ 100mV) to
20
s
V
IN
= (V
REF(MIN)
100mV), /MR = open;
t
RST
Reset Pulse Width
T
MIN
T
A
T
MAX
140
280
ms
V
OL
RST or /RST Output Voltage Low
I
SINK
= 1.6mA;
0.3
V
V
DD
1.6V
I
SINK
= 100
A;
0.3
V
V
DD
1.2V; Note 4
V
OH
RST or /RST Output Voltage High
I
SOURCE
= 500
A;
0.8V
DD
V
V
DD
1.5V
(H and L Version Only)
I
SOURCE
= 10
A;
0.8V
DD
V
V
DD
1.2V; Note 4
/MR INPUTS
V
IH
Input High Voltage
Note 5
0.7V
DD
V
V
IL
Input Low Voltage
Note 5
0.3V
DD
V
t
PROP
Propagation Delay
V
/MR
< (V
IL
100mV); Note 5
5
s
t
MIN
Minimum Input Pulse Width
Reset Occurs, V
/MR
< V
IL
33
ns
I
PU
Internal Pull-up Current
100
nA
I
IN
Input Current, /MR
V
/MR
< V
IL
100
nA
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
Note 4.
V
DD
operating range is 1.5V to 5.5V. Output is guaranteed to be asserted down to V
DD
= 1.2V.
Note 5.
V
DD
equals nominal "Typical Application (V
DD
)" as shown in "Standard Voltage Options Table."
MIC2774
Micrel
MIC2774
4
September 29, 2000
Timing Diagram
V
/MR
V
IH
V
IL
V
IN
0V
V
TH
V
DD
0V
V
/RST
(ACTIVE LOW)
V
OH
V
OL
V
RST
(ACTIVE HIGH)
V
OH
V
OL
t
RST
t
RST
> t
MIN
t
RST
V
HYST
A
A
A
V
REF
V
HYST
Propagation delays not shown for clarity.
Note A.
The MIC2774 ignores very brief transients.
See "Applications Information" for details.
September 29, 2000
5
MIC2774
MIC2774
Micrel
Functional Diagram
GND
V
DD
/MR
IN
MIC2774
* Pinout and polarity vary by device type.
See ordering information table.
V
REF
V
V
DD
REF
RST*
R
S
Q
/Q
/RST*
Delay
Line
One Shot
I
PU
Functional Description
IN, Under-Voltage Detector Input
The voltage present at the IN pin is compared to the internal
300mV reference voltage. A reset is triggered if and when V
IN
falls below V
REF
. Typically, a resistor divider is used to scale
the input voltage to be monitored such that V
IN
will fall below
V
REF
as the voltage being monitored falls below the desired
trip-point. Hysteresis is employed to prevent chattering due to
noise. The comparator on the IN pin is relatively immune to
very brief negative-going transients.
V
DD
Input
The V
DD
pin is both the power supply terminal and a moni-
tored input voltage. The voltage at this pin is continually
compared against the internal reference. The trip-point at
which a reset occurs is factory programmed. A reset is
triggered if and when V
DD
falls below the trip-point. Hyster-
esis is employed to prevent chattering due to noise. The
comparator on the V
DD
input is relatively immune to very brief
negative-going transients.
RST, /RST Reset Output
Typically, the MIC2774 is used to monitor the power supplies
of intelligent circuits such as microcontrollers and micropro-
cessors. By connecting the appropriate reset output of a
MIC2774 to the reset input of a
C or P, the processor will
be properly reset at power-on and during power-down and
brown-out conditions. In addition, asserting /MR, the manual
reset input, will activate the reset function.
The reset output is asserted any time /MR is asserted or if V
IN
or V
DD
drops below the corresponding threshold voltage. The
reset output remains asserted for t
RST
(min) after V
IN
and/or
V
DD
subsequently return above the threshold boundaries
and/or /MR is released. A reset pulse is also generated at
power-on. Hysteresis is included in the comparators to pre-
vent chattering of the output due to noise.
/MR, Manual Reset Input
The ability to initiate a reset via external logic or a manual
switch is provided in addition to the MIC2774's automatic
supervisory functions. Driving the /MR input to a logic low
causes an immediate and unconditional reset to occur.
Assuming V
IN
and V
DD
are within tolerance when /MR is
released (returns high), the reset output will be de-asserted
no less than t
RST
later. /MR may be driven by a logic signal,
or mechanical switch. Typically, a momentary push-button
switch is connected such that /MR is shorted to ground when
the switch contacts close. Switch de-bouncing is performed
internally; the switch may be connected directly between /MR
and GND. /MR is internally pulled-up to V
DD
and may be left
open if unused.
MIC2774
Micrel
MIC2774
6
September 29, 2000
Application Information
Programming the Voltage Threshold
Referring to the "Typical Application Circuit", the voltage
threshold on the IN pin is calculated as follows:
V
V
R1 R2
R2
TH
REF
=
+
(
)
where V
REF
= 0.300V
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
TOTAL
. Imposing this condition on the resistor values pro-
vides two equations that can be solved for the two unknown
resistor values. A value such as 1M
for R
TOTAL
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
IN
). The
maximum recommended value of R
TOTAL
is 3M
.
Applying this criteria and rearranging the V
TH
expression to
solve for the resistor values gives:
R2
R
V
V
TOTAL
REF
TH
=
(
)
(
)
R1
R
R2
TOTAL
=
-
Application Example
Figure 1 below illustrates a hypothetical MIC2774L-23 appli-
cation 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
CORE
, in the example is 1.0V
5%. The main
power rail and I/O voltage, V
I/O
, is 2.5V
5%. As shown in
Figure 1, the MIC2774 is powered by V
I/O
. The minimum
value of V
I/O
is 2.5V 5% = 2.375V; the maximum is 2.5V +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
CORE
supply of 1.0V. The goal is to insure that the core
supply voltage is adequate to insure proper operation, i.e.,
V
CORE
(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 poten-
tial variation in the MIC2774's voltage reference (V
REF
) 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 contri-
bution 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.
To summarize, the various potential error sources are:
Variation in V
REF
:
specified at
1.5%
Resistor tolerance:
chosen by designer (typically
1%)
Input bias current, I
IN
:
calculated once resistor values are known, typically
very small
Taking the various potential error sources into account, the
threshold voltage will be set slightly below the minimum
V
CORE
specification of 0.950V so that when the actual thresh-
old voltage is at its maximum, it will not intrude into the normal
operating range of V
CORE
. The target threshold voltage will
be set as follows:
Given that the total tolerance on V
TH
for the IN pin is [V
REF
tolerance] + [resistor tolerance]
=
1.5% + 1% = 2.5%,
and V
TH(max)
= V
CORE(min)
,
then V
CORE(min)
= V
TH
+ 2.5% V
TH
= 1.025 V
TH
,
therefore, solving for V
TH
results in
V
=
V
1.025
=
0.950
1.025
= 0.9268V
TH
CORE(min)
Solving for R1 and R2 using this value for V
TH
and the
equations above yields:
R1 = 676.3k
673k
R2 = 323.7k
324k
The resulting circuit is shown in Figure 1.
Input Bias Current Effects
Now that the resistor values are known, it is possible to
calculate the maximum potential error due to input bias
current, I
IN
. As shown in the "Electrical Characteristics" table,
the maximum value of I
IN
is 10nA. (Note that the typical value
is a much smaller 5pA!) The magnitude of the offset caused
by I
IN
is given by:
V
I
R1|| R2
ERROR
IN(max)
=
(
)
=
V
1 10
A
2.189 10
=
ERROR
5
=
-8
V
2.189 10
V =
ERROR
3
=
-
V
2.189mV
ERROR
=
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
TOTAL
to minimize
offset errors.
September 29, 2000
7
MIC2774
MIC2774
Micrel
IN
/RST
VDD
/MR
GND
MIC2774L-23
R1
676k
1%
R2
324k
1%
/RESET
VCORE
GND
V
CORE
1.0V
5%
Manual
Reset
MICROPROCESSOR
VI/O
V
I/O
2.5V
5%
Figure 1. MIC2774 Example Design
Interfacing to Processors With Bidirectional Reset Pins
Some microprocessors have reset signal pins that are bidi-
rectional, rather than input only. The Motorola 68HC11 family
is one example. Because the MIC2774N's output is open-
drain, it can be connected directly to the processor's reset pin
using only the pull-up resistor normally required. See Figure 2.
IN
/RST
VDD
/MR
GND
MIC2774N-XX
R1
R2
/RESET
VCC
GND
V
CC
MICROPROCESSOR
100k
Figure 2. Interfacing to Bidirectional Reset Pin
Transient response
The MIC2774 is inherently immune to very short negative-
going "glitches." Very brief transients may exceed the voltage
thresholds without tripping the output.
As shown in Figure 3a and 3b, in general the narrower the
transient, the deeper the threshold overdrive that will be
ignored by the MIC2774. The graphs represent the typical
allowable transient duration for a given amount of threshold
overdrive that will not generate a reset.
0
5
10
15
20
25
30
35
40
0
100
200
300
MAX. TRANSIENT DURATION (
s)
RESET COMP. OVERDRIVE, V
REF
V
IN
(mV)
Typical IN
Transient Response
Figure 3a. Typical INPUT Transient Response
0
20
40
60
80
100
0
500
1000
1500
2000
MAX. TRANSIENT DURATION (
s)
RESET COMP. OVERDRIVE, V
REF
V
DD
(mV)
Typical V
DD
Transient Response
Figure 3b. Typical V
DD
Transient Response
Ensuring Proper Operation at Low Supply
At levels of V
DD
below 1.2V, the MIC2774's reset output
cannot turn on sufficiently to produce a valid logic-low on
/RST. In this situation, circuits driven by /RST could be
allowed to float, causing undesired operation. (In most cases,
however, it is expected that the circuits driven by the MIC2774L
will be similarly inoperative at V
DD
1.2V.)
If a given application requires that /RST be valid below V
DD
= 1.2V, this can be accomplished by adding a pull-down
resistor to the /RST output. A value of 100k
is recom-
mended as this is usually an acceptable compromise of
quiescent current and pull-down current. The resistor's value
is not critical, however. See Figure 4.
The statements above also apply to the MIC2774H's RST
output. That is, to ensure valid RST signal levels at V
DD
<
1.2V, a pull-up resistor (as opposed to a pull-down) should be
added to the RST output. A value of 100k
is typical for this
application as well. See Figure 5.
IN
/RST
VDD
/MR
GND
MIC2774L-XX
R1
R2
/RESET
VCC
GND
V
CC
Manual
Reset
MICROPROCESSOR
100k
Rpull-down
Figure 4. MIC2774L Valid /RST Below 1.2V
IN
RST
VDD
/MR
GND
MIC2774H-XX
R1
R2
RESET
VCC
GND
V
CC
Manual
Reset
MICROPROCESSOR
100k
Rpull-up
Figure 5. MIC2774H Valid RST Below 1.2V
MIC2774
Micrel
MIC2774
8
September 29, 2000
Package Information
0.20 (0.008)
0.09 (0.004)
0.60 (0.024)
0.10 (0.004)
3.02 (0.119)
2.80 (0.110)
10
0
3.00 (0.118)
2.60 (0.102)
1.75 (0.069)
1.50 (0.059)
0.95 (0.037) REF
1.30 (0.051)
0.90 (0.035)
0.15 (0.006)
0.00 (0.000)
DIMENSIONS:
MM (INCH)
0.50 (0.020)
0.35 (0.014)
1.90 (0.075) REF
SOT-23-5 (M5)
MICREL INC.
1849 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
2000 Micrel Incorporated
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