January 2005 1 M9999-011405
MIC2774 Micrel
MIC2774
Dual Micro-Power Low Voltage Supervisor
General Description
The MIC2774 is a dual power supply supervisor that pro-
vides under-voltage monitoring, manual reset capability, and
power-on reset generation in a compact 5-pin SOT package.
Features include two under-voltage detectors, one fixed and
one adjustable, and a choice of reset outputs. One under-
voltage detector compares VDD against a fixed threshold. Ten
factory-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 con-
nected 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 3.5µA.
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
VI/O 2.5V
Features
• Monitors two independent power supplies for under-volt-
age 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 VDD (7V abs. max.)
• Open-drain output can be pulled above VDD (7V abs
max.)
• /RST output valid down to 1.2V
• Ultra-low supply current, 3.5µA typical
• Rejects brief input transients
• IttyBitty™ 5-lead SOT-23 package
• Pin compatible upgrade for MAX6306/09/12
Applications
• Monitoring processor ASIC, or FAGA core and I/O volt-
ages
• PDAs, hand-held PCs
• Embedded controllers
• Telecommunications systems
• Power supplies
• Wireless / Cellular systems
• Networking hardware
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
IttyBitty™ is a trademark of Micrel, Inc.
Ordering Information
Part Number Reset Output Temperature
Range
Package
Standard Marking Pb-Free Marking
MIC2774N-XXBM5 UGXX* MIC2774N-XX M5 UGXX* Open-Drain. Active-Low (/RST) -40°C to +85°C SOT-23-5
MIC2774H-XXBM5 UHXX* MIC2774H-XX M5 UHXX* Active-High. Complementary (RST) -40°C to +85°C SOT-23-5
MIC2774L-XXBM5 UIXX* MIC2774L-XX M5 UIXX* Active-Low. Complementary (/RST) -40°C to +85°C SOT-23-5
* XX = Voltage options, see table on page 2. Underscore indicates a Pb-Free part.
MIC2774 Micrel
M9999-011405 2 January 2005
Pin Configuration
RST
VDDIN
/MR
13
4 5
2
GND
SOT-23-5 (M5)
“H” Version
/RST
VDDIN
/MR
13
4 5
2
GND
SOT-23-5 (M5)
“L” and “N” Version
Standard Voltage Options*
Voltage Typical Nominal Threshold
Code Application (VDD) Voltage (VTH)
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 VIN or VDD falls below the threshold
voltage. It will remain asserted for no less than 140ms after VIN and VDD
return above the threshold limits.
1 /RST Digital (Output): Asserted low whenever VIN or VDD falls below the threshold
voltage. It will remain asserted for no less than 140ms after VIN and VDD
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 re-
set. Assuming VIN and VDD 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 VDD 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.
January 2005 3 M9999-011405
MIC2774 Micrel
Absolute Maximum Ratings (Note 1)
Supply Voltage (VDD) .......................................–0.3V to +7V
Input Voltages (VIN, V/MR) ...............................–0.3V to +7V
Output Voltages (V/RST, VRST) .........................–0.3V to +7V
RST, (/RST) Current ................................................... 20mA
Storage Temperature (TS) ........................ –65°C to +150°C
ESD Rating, Note 3 .................................................... 1.5kV
Operating Ratings (Note 2)
Supply Voltage (VDD) .................................. +1.5V to +5.5V
Input Voltages (VIN, V/MR) ............................–0.3V to +6.0V
Output Voltages
V/RST (N version), ....................................–0.3V to +6.0V
V/RST, VRST (H and L versions) .......... –0.3V to VDD+0.3V
Ambient Temperature Range (TA) .............. –40°C to +85°C
Package Thermal Resistance (θJA) ....................... 256°C/W
Electrical Characteristics
Note 5; TA = +25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Symbol Parameter Condition Min Typ Max Units
IDD Supply Current VDD = VIN = VTH +1.6%, 3.5 µA
Note 5; /MR, RST, /RST open
VDD VOLTAGE THRESHOLD
Under-Voltage Threshold On VDD
VTH–1.5%
VTH
VTH+1.5%
V
(See Standard Voltage Options Table)
VHYST Hysteresis Voltage 1 %
IN, UNDER-VOLTAGE DETECTOR INPUT
VREF Under-Voltage Threshold Note 5 295 300 305 mV
VHYST Hysteresis Voltage 3 mV
IIN Input Current 5 pA
TMIN ≤ TA ≤ TMAX 10 nA
RST, /RST OUTPUTS
tPROP Propagation Delay VIN = (VREF(MAX) + 100mV) to 20 µs
VIN = (VREF(MIN) – 100mV), /MR = open;
tRST Reset Pulse Width TMIN ≤ TA ≤ TMAX 140 280 ms
VOL RST or /RST Output Voltage Low ISINK = 1.6mA; 0.3 V
VDD ≥ 1.6V
ISINK = 100µA; 0.3 V
VDD ≥ 1.2V; Note 4
VOH RST or /RST Output Voltage High ISOURCE = 500µA; 0.8VDD V
VDD ≥ 1.5V
(H and L Version Only) ISOURCE = 10µA; 0.8VDD V
VDD ≥ 1.2V; Note 4
/MR INPUTS
VIH Input High Voltage Note 5 0.7VDD V
VIL Input Low Voltage Note 5 0.3VDD V
tPROP Propagation Delay V/MR < (VIL –100mV); Note 5 5 µs
tMIN Minimum Input Pulse Width Reset Occurs, V/MR < VIL 33 ns
IPU Internal Pull-up Current 100 nA
IIN Input Current, /MR V/MR < VIL 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. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be asserted down to VDD = 1.2V.
Note 5. VDD equals nominal “Typical Application (VDD)” as shown in “Standard Voltage Options Table.”
MIC2774 Micrel
M9999-011405 4 January 2005
Timing Diagram
V/MR
VIH
VIL
VIN
0V
VTH
VDD
0V
V/RST
(ACTIVE LOW)
VOH
VOL
VRST
(ACTIVE HIGH)
VOH
VOL
tRST tRST
> tMIN
tRST
VHYST
AAA
VREF
VHYST
Propagation delays not shown for clarity.
Note A. The MIC2774 ignores very brief transients.
See “Applications Information” for details.
January 2005 5 M9999-011405
MIC2774 Micrel
Functional Diagram
GND
VDD
/MR
IN
MIC2774
* Pinout andpolarity vary by device type.
See ordering information table.
V
REF
V
VDD
REF
RST*
R
S
Q
/Q
/RST*
Delay
Line
One Shot
IPU
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 VIN
falls below VREF. Typically, a resistor divider is used to scale
the input voltage to be monitored such that VIN will fall below
VREF 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.
VDD Input
The VDD pin is both the power supply terminal and a monitored
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 VDD falls below the trip-point. Hysteresis is employed
to prevent chattering due to noise. The comparator on the
VDD 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 µC or µP, 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 VIN
or VDD drops below the corresponding threshold voltage. The
reset output remains asserted for tRST(min) after VIN and/or
VDD 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 prevent
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 VIN and VDD are within tolerance when /MR is
released (returns high), the reset output will be de-asserted
no less than tRST 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 VDD and may
be left open if unused.
MIC2774 Micrel
M9999-011405 6 January 2005
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 VREF = 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 = RTOTAL. Imposing this condition on the resistor val-
ues provides two equations that can be solved for the two
unknown resistor values. A value such as 1MΩ for RTOTAL
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 (IIN). The
maximum recommended value of RTOTAL is 3MΩ.
Applying this criteria and rearranging the VTH 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 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, VCORE, in the example is 1.0V ±5%. The
main power rail and I/O voltage, VI/O, is 2.5V ±5%. As shown
in Figure 1, the MIC2774 is powered by VI/O. The minimum
value of VI/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
VCORE supply of 1.0V. The goal is to insure that the core
supply voltage is adequate to insure proper operation, i.e.,
VCORE ≥ (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 po-
tential variation in the MIC2774’s voltage reference (VREF)
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 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.
To summarize, the various potential error sources are:
• Variation in VREF: specified at ±1.5%
• Resistor tolerance:
chosen by designer (typically ≤ ±1%)
• Input bias current, IIN:
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 VCORE
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 VCORE. The target threshold voltage will
be set as follows:
Given that the total tolerance on VTH for the IN pin is [VREF
tolerance] + [resistor tolerance]
= ±1.5% + ±1% = ±2.5%,
and VTH(max) = VCORE(min),
then VCORE(min) = VTH + 2.5% VTH = 1.025 VTH,
therefore, solving for VTH results in
Solving for R1 and R2 using this value for VTH and the equa-
tions above yields:
R1 = 676.3kΩ ≈ 673kΩ
R2 = 323.7kΩ ≈ 324kΩ
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,
IIN. As shown in the “Electrical Characteristics” table, the
maximum value of IIN is 10nA. (Note that the typical value
is a much smaller 5pA!) The magnitude of the offset caused
by IIN is given by:
V I R1 || R2
ERROR IN(max)
= ×
( )
=
V 1 10 A 2.189 10 =
ERROR 5
= ± × × ×
−8Ω
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 RTOTAL to minimize
offset errors.
January 2005 7 M9999-011405
MIC2774 Micrel
IN
/RST
VDD
/MR GND
MIC2774L-23
R1
676k
1%
R2
324k
1%
/RESET
VCORE
GND
VCORE
1.0V 5%
Manual
Reset
MICROPROCESSOR
VI/O
VI/O
2.5V 5%
Figure 1. MIC2774 Example Design
Interfacing to Processors With Bidirectional Reset Pins
Some microprocessors have reset signal pins that are bi-
directional, 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
VCC
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 (µs)
RESET COMP. OVERDRIVE, VREF –V IN (mV)
Typical IN
Trans ient R es pons e
Figure 3a. Typical INPUT Transient Response
0
20
40
60
80
100
0 500 1000 1500 2000
MAX. TRANSIENT DURATION (µs)
RESET COMP. OVERDRIVE, VREF –V DD (mV)
Typic al VDD
Trans ient R es pons e
Figure 3b. Typical VDD Transient Response
Ensuring Proper Operation at Low Supply
At levels of VDD below 1.2V, the MIC2774’s reset output can-
not 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 VDD ≤ 1.2V.)
If a given application requires that /RST be valid below VDD
= 1.2V, this can be accomplished by adding a pull-down re-
sistor to the /RST output. A value of 100kΩ is recommended
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 VDD <
1.2V, a pull-up resistor (as opposed to a pull-down) should
be added to the RST output. A value of 100kΩ is typical for
this application as well. See Figure 5.
IN
/RST
VDD
/MR GND
MIC2774L-XX
R1
R2
/RESET
VCC
GND
VCC
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
VCC
Manual
Reset
MICROPROCESSOR
100k
Rpull-up
Figure 5. MIC2774H Valid RST Below 1.2V
MIC2774 Micrel
M9999-011405 8 January 2005
Package Information
SOT-23-5 (M5)
MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's
use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2004 Micrel Incorporated