Datasheet

MIC2774
Dual Micro-Power Low Voltage Supervisor
General Description
Features
The MIC2774 is a dual power supply supervisor that
provides undervoltage monitoring, manual reset capability,
and power-on reset generation in a compact 5-pin SOT-23
package. Features include two undervoltage detectors,
one fixed and one adjustable, and a choice of reset
outputs. One undervoltage 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 for the monitoring of voltages lower than those
supported by previous supervisor ICs.
• Monitors two independent power supplies for
undervoltage conditions
• One fixed and one user-adjustable input
• Choice of ten factory-programmed thresholds
• Adjustable input can monitor supplies as low as 0.3V
• Generates 140ms (min.) power-on reset pulse
• Manual reset input
• Choice of active-high, active-low, or open-drain activelow reset outputs
• Inputs may 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-pin SOT-23 package
• Pin-compatible upgrade for MAX6306/09/12
The reset outputs are asserted at power-on and at any
time either voltage drops below the programmed threshold
voltage 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 3.5µA.
Datasheets and support documentation are available on
Micrel’s website at: www.micrel.com.
Applications
• Monitoring processor ASIC or FPGA core and I/O
voltages
• PDAs, hand-held PCs
• Embedded controllers
• Telecommunications systems
• Power supplies
• Wireless/cellular systems
• Networking hardware
Typical Application
IttyBitty is a trademark of Micrel, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
March 16, 2015
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MIC2774
Ordering Information
(1,2)
(1,3)
Part Number
Marking
Reset Output
Junction Temperature Range
Package
(4)
MIC2774N-XXYM5
UGXX
Open-Drain. Active-Low (/RST)
–40°C to +85°C
SOT-23-5
MIC2774H-XXYM5
UHXX
Active-High. Complementary (RST)
–40°C to +85°C
SOT-23-5
MIC2774L-XXYM5
UIXX
Active-Low. Complementary (/RST)
–40°C to +85°C
SOT-23-5
Note:
1. XX = voltage code, see table below.
2. Order entry part number, add “ TR”. Example: MIC2774N-22YM5 TR.
3. Underbar symbol (__) may not be to scale.
4. Standard reel SOT-23: Reel diameter is 7 inches, hub diameter is 2 inches, width is 8mm.
Standard Voltage Options(5)
Voltage Code
Typical Application (VDD)
Nominal Threshold Voltage (VTH)
46
5.0V ±5%
4.68V
44
5.0V ±10%
4.43V
31
3.3V ±5%
3.09V
29
3.3V ±10%
2.93V
28
3.0V ±5%
2.81V
26
2.85V ±5%
2.67V
25
2.7V ±5%
2.53V
23
2.5V ±5%
2.34V
22
2.4V ±5%
2.25V
17
1.8V ±5%
1.69V
Note:
5. There are ten standard versions available with an order increment of 3,000 pieces. Samples of standard versions are normally available from stock.
Contact factory for information on non-standard versions. Available in tape-and-reel only.
Part Number Convention
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Pin Configuration
SOT-23-5 (M5)
“H” Version
SOT-23-5 (M5)
“L” and “N” Version
Pin Description
Pin Number
MIC2774H
Pin Number
MIC2774L
MIC2774N
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, requires an external
pull-up resistor).
2
GND
Ground
Digital (Input): Driving this pin low initiates immediate and unconditional reset.
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.
3
3
/MR
4
4
IN
5
5
VDD
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Pin Function
RST
1
2
Pin Name
Analog (Input): The voltage on this pin is compared to the internal 300mV
reference. An undervoltage condition will trigger a reset sequence.
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.
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Absolute Maximum Ratings(6)
Operating Ratings(7)
Supply Voltage (VDD) .................................... –0.3V to +7.0V
Input Voltages (VIN, V/MR) ............................. –0.3V to +7.0V
Output Voltages (V/RST, VRST) ....................... –0.3V to +7.0V
RST, (/RST) Current ................................................... 20mA
Storage Temperature (Ts)......................... –65°C to +150°C
(8)
ESD Rating ............................................................... 1.5kV
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 to +0.3V
Ambient Temperature (TA) .......................... –40°C to +85°C
Package Thermal Resistance (θJA) ........................ 256°C/W
Electrical Characteristics(9)
Note 10; TA = +25°C, bold values indicate –40°C≤ TA ≤ +85°C, unless noted.
Symbol
Parameter
Condition
Min.
IDD
Supply Current
VDD = VIN = VTH + 1.6%;
Note 10; /MR, RST, /RST open
Typ.
Max.
3.5
Units
µA
VDD Voltage Threshold
Undervoltage Threshold on VDD
(See Standard Voltage Options
table)
VHYST
VTH1.5%
Hysteresis Voltage
VTH
VTH+
1.5%
1
V
%
IN, Undervoltage Detector Input
VREF
Undervoltage Threshold
VHYST
Hysteresis Voltage
IIN
Input Current
295
Note 10
300
305
mV
3
mV
5
pA
TMIN ≤ TA ≤ TMAX
10
nA
RST, /RST Outputs
tPROP
Propagation Delay
VIN = (VREF(MAX) + 100mV) to
VIN = (VREF(MIN) – 100mV), /MR = open
tRST
Reset Pulse Width
TMIN ≤ TA ≤ TMAX
VOL
RST or /RST Output Voltage
Low
VOH
RST or /RST Output Voltage
High (H and L versions)
20
140
µs
280
ms
ISINK = 1.6mA; VDD ≥ 1.6V
0.3
V
ISINK = 100µA; VDD ≥ 1.2V; Note 11
0.3
V
ISOURCE = 500µA; VDD ≥ 1.5V
0.8 ×
VDD
V
ISOURCE = 10µA; VDD ≥ 1.2V; Note 11
0.8 ×
VDD
V
Notes:
6. Exceeding the absolute maximum ratings may damage the device.
7. The device is not guaranteed to function outside its operating ratings.
8. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF.
9. Specification for packaged product only
10. VDD equals nominal “Typical Application (VDD)” as shown in the Standard Voltage Options table.
11. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be asserted down to VDD = 1.2V.
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Electrical Characteristics(9)
Note 10; TA = +25°C, bold values indicate –40°C≤ TA ≤ +85°C, unless noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
VIH
Input High Voltage
Note 10
0.7 ×
VDD
VIL
Input Low Voltage
Note 10
tPROP
Propagation Delay
V/MR < (VIL – 100mV); Note 10
5
µs
tMIN
Minimum Input Pulse Width
Reset occurs, V/MR < VIL
33
ns
IPU
Internal Pull-Up Current
IIN
Input Current, /MR
/MR Inputs
V
0.3 ×
VDD
V/MR < VIL
%
100
250
nA
100
250
nA
Timing Diagram
Notes:
12. Propagation delays not shown for clarity.
13. The MIC2774 ignores very brief transients. See the Application Information section for details.
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Functional Diagram
Note: *Pinout and polarity vary by device type. See the Ordering Information table.
RST, /RST Reset Output
Typically, the MIC2774 is used to monitor the power
supplies of intelligent circuits such as microcontrollers
and microprocessors. By connecting the appropriate
reset output of an MIC2774 to the reset input of a µC or
µP, the processor will be properly reset at power-on,
power-down, and during brown-out conditions. In
addition, asserting /MR, the manual reset input, will
activate the reset function.
Functional Description
IN, Undervoltage 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 immunue to very
brief negative-going transients.
The reset output is asserted any time /MR is asserted of
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
isincluded in the comparators to prevent chattering of the
output due to noise.
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 trippoint. Hysteresis is employed to prevent chattering due to
noise. The comparator on the VDD input is relatively
immune to very brief negative-going transients.
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/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 deasserted 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 debouncing 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.
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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.
Application Information
Programming the Voltage Threshold
Referring to the Typical Application circuit, the voltage
threshold on the IN pin is calculated as follows:
VIH = VREF ×
To summarize, the various potential error sources are:
(1+2)
2
where VREF = 0.300V
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 slight 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:
In order to provide the additional criteria needed to solve
for the resistor values, the resistorscan be selected such
that the two resistors have a given total value; that is, R1
+ R2 = RTOTAL. Imposing this condition on the resistor
values provides two equations that can be solved for the
two unknown resistor values. A value such as 1MΩ for
RTOTAL is a reasonable choice because 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.
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,
Applying this criteria and rearranging the VIH expression
to solve for the resistor values gives:
R2 =
•
therefore, solving for VTH results in
VTH =
( )()

 (min)
1.025
=
0.950
1.025
= 0.9268
Solving for R1 and R2 using this value for VTH and the
equations above yields:
R1 = RTOTAL – R2
R1 = 676.3kΩ ≈ 673kΩ
Application Example
Figure 1 illustrates a hypothetical MIC2774L-23
application 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.
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
calculate 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:
Resistors R1 and R2 must be selected to correspond to
the VCORE supply of 1.0V. The goal is to ensure that the
core supply voltage is adequate to ensure 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 device’s
voltage reference, etc., the threshold will be set slightly
below this value. The potential variation in the MIC2774’s
voltage reference (VREF) is specified as ±1.5%. The
resistors chosen will have their own tolerance
specifications. This example assumes 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
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VERROR = IIN(max) × (R1||R2) =
VERROR = ±1×10 A × 2.189×10 Ω =
-8
5
-3
VERROR = ±2.189×10 V =
VERROR = ±2.189mV
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
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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.
the resistors, simply reduce the value of RTOTAL to
minimize offset errors.
In general, as shown in Figure 3 and Figure 4, the
narrower the transient, the deeper the threshold overdrive
that the MIC2774 will ignore. The graphs represent the
typical allowable transient duration for a given amount of
threshold overdrive that will not generate a reset.
Figure 1. MIC2774 Example Design
Interfacing to Processors with Bidirectional Reset
Pins
Some microprocessors have reset signal pins that are
bidirectional, 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.
Figure 3. Typical Input Transient Response
Figure 4. Typical VDD Transient Response
Ensuring Proper Operation at Low Supply
At VDD levels 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 VDD ≤ 1.2V.
Figure 2. Interfacing to Bidirectional Reset Pin
If a given application requires that /RST be valid below
VDD = 1.2V, this can be accomplished by adding a pulldown resistor to the /RST output. A value of 100kΩ is
recommended because this is usually an acceptable
compromise of quiescent current and pull-down current.
The resistor’s value is not critical, however. See Figure 5.
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MIC2774
These statements 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 6.
Figure 5. MIC2774L Valid /RST Below 1.2V
Figure 6. MIC2774H Valid RST Below 1.2V
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Package Information and Recommended Landing Pattern(14)
SOT-23-5 (M5)
Note:
14. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.
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MIC2774
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TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
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