MIC2777
Micrel, Inc.
MIC2777
Dual Micro-Power Low Voltage Supervisor
General Description
The MIC2777 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 both active-high and active-low reset outputs.
One under-voltage detector compares V
DD
against a fixed
threshold. Ten factory-programmed thresholds are available.
The other under-voltage detector is user-adjustable.
The reset outputs are asserted for no less than 140ms at
power-on and any time V
DD
or the input voltage drops below
the corresponding reference voltage. They remain asserted
for the timeout period after the input voltage and V
DD
sub-
sequently rise back above the threshold boundaries. A reset
can be generated at any time by pulling down on the adjust-
able input. Hysteresis is included to prevent chattering due
to noise. Typical supply current is a low 3.5µA.
Features
• Monitors two independent power supplies for under-volt-
age conditions
• One fixed and one user adjustable input
• 1.5% theshold accuracy
• Choice of factory-programmed thresholds
• User-adjustable input can monitor supplies as low as
0.3V
• Generates 140ms (minimum) power-on RESET pulse
• Manual reset capability
• Both active-high and active-low RESET outputs
• Input may be pulled above V
DD
(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
Applications
• Monitoring processor, ASIC, or FPGA core and I/O volt-
ages
• Computer systems
• PDAs, hand-held PCs
• Embedded controllers
• Telecommunications systems
• Power supplies
• Wireless / Cellular systems
• Networking hardware
Ordering Information
Part Number
Standard
Marking Pb-Free
MIC2777-XXYM5
Marking
UNXX
MIC2777-XXBM5 UNXX
Junction Tem. Range
–40ºC to +85ºC
Package
SOT-23-5
Typical Application
V
CORE
1.0V
V
I/O
1.8V
R1
R2
MIC2777
VDD /RST
IN
RST
MICROPROCESSOR
V
CORE
V
I/O
/RESET
GND
GND
Manual
Reset
OTHER
LOGIC
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
November 2005
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MIC2777
MIC2777
Micrel, Inc.
Standard Voltage Options*
Voltage
Code
46
44
31
29
28
26
25
23
22
17
Typical
Application (V
DD
)
5.0V ±5%
5.0V ±10%
3.3V ±5%
3.3V ±10%
3.0V ±5%
2.85V ±5%
2.70V ±5%
2.5V ±5%
2.4V ±5%
1.8V ±5%
Nominal Threshold
Voltage (V
TH
)
4.68
4.43
3.09
2.93
2.81
2.67
2.53
2.34
2.25
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 Configuration
RST GND /RST
3
2
1
4
5
IN
VDD
SOT-23-5 (M5)
Pin Description
Pin Number
1
Pin Name
/RST
Pin Function
Digital (Output): Asserted low whenever V
IN
or V
DD
falls below the reference
voltage. It will remain asserted for no less than 140ms after V
IN
and V
DD
return above the threshold limits.
Ground
Digital (Output): Asserted high whenever V
IN
or V
DD
falls below the refer-
ence voltage. It will remain asserted for no less than 140ms after V
IN
and
V
DD
return within above the threshold limit.
2
3
GND
RST
4
IN
Analog (Input): The voltage on this pin is compared to the internal 300mV
reference. An undervoltage condition will trigger a reset sequence. Manual
reset capability can be achieved by adding a switch between this pin and
ground.
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
voltage reference. An undervoltage condition will trigger a reset sequence.
5
VDD
MIC2777
2
November 2005
MIC2777
Micrel, Inc.
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
DD
).......................................–0.3V to +7V
Input Voltage (V
IN
) ...........................................–0.3V to +7V
RST, (/RST) Current ................................................... 20mA
Storage Temperature (T
S
) ........................ –65°C to +150°C
ESD Rating,
Note 3
.................................................... 1.5kV
Operating Ratings
(Note 2)
Supply Voltage (V
DD
) .................................. +1.5V to +5.5V
Input Voltage
(V
IN
) .............................................................–0.3V to +6.0V
Ambient Temperature Range (T
A
) .............. –40°C to +85°C
Package Thermal Resistance (θ
JA
) ....................... 256°C/W
Electrical Characteristics
Note 5;
T
A
= +25°C,
bold
values indicate –40°C ≤ T
A
≤ +85°C; unless noted
Symbol
Parameter
Condition
I
DD
Supply Current
V
DD
= V
IN
Note 5;
/MR, RST, /RST open
V
TH
-1.5%
Min
Typ
3.5
Max
Units
µA
VDD VOLTAGE THRESHOLD
V
HYST
V
REF
I
IN
Under-Voltage Threshold On V
DD
Hysteresis Voltage
V
TH
1
V
TH
+1.5%
V
%
mV
mV
pA
10
20
nA
µs
IN, UNDER-VOLTAGE DECTECTOR INPUT
Under-Voltage Threshold
Hysteresis Voltage
Input Current
T
MIN
≤ T
A
≤ T
MAX
V
IN
= (V
REF(MAX)
+ 100mV) to
V
IN
= (V
REF(MIN)
– 100mV) or
V
DD
= (V
TH
+ 2.5%) to (V
TH
– 2.5%), V
IN
=V
DD
I
SINK
= 1.6mA;
V
DD
≥ 1.6V
295
300
3
5
305
V
HYST
RST, /RST OUTPUTS
t
PROP
t
RST
V
OL
Propagation Delay
Reset Pulse Width
RST or /RST Output Voltage Low
140
280
0.3
0.3
ms
V
V
V
V
V
OH
RST or /RST Output Voltage High
RST asserted, I
SOURCE
= 10µA;
V
DD
≥ 1.2V,
Note 4
Note 1.
Note 2.
Note 3.
Note 4.
Note 5.
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
I
SOURCE
= 500µA;
V
DD
≥ 1.5V
I
SINK
= 100µA;
V
DD
≥ 1.2V,
Note 4
0.8V
DD
0.8V
DD
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
V
DD
operating range is 1.5V to 5.5V. Output is guaranteed to be asserted down to V
DD
= 1.2V.
V
DD
equals the nominal “Typical Application (V
DD
)” as shown in “Standard Voltage Options Table.”
November 2005
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MIC2777
MIC2777
Micrel, Inc.
V
DD
0V
V
IN
0V
V
/RST
V
OH
V
OL
V
OH
V
OL
Propagation delays not shown for clarity.
Note A.
The MIC2777 ignores very brief transients.
See “Applications Information” for details.
Timing Diagram
A
A
V
HYST
V
TH
A
V
HYST
V
REF
(ACTIVE LOW)
t
RST
t
RST
V
RST
(ACTIVE HIGH)
MIC2777
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November 2005
MIC2777
Micrel, Inc.
Functional Diagram
V
DD
R
V
REF
IN
Delay
Line
One Shot
Q
/RST
S /Q
RST
V
REF
MIC2777
GND
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 input is relatively immune
to very brief negative-going transients.
V
DD
Input
The V
DD
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 V
DD
falls below the trip-point. Hysteresis 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 MIC2777 is used to monitor the power supplies
of intelligent circuits such as microcontrollers and micropro-
cessors. By connecting the appropriate reset output of a
MIC2777 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.
The reset outputs are asserted any time V
DD
or V
IN
drops
below the corresponding threshold voltage. The reset outputs
remain asserted for t
RST
(min) after V
IN
and/or V
DD
subsequent
return above the threshold boundaries and/or /MR is released.
A reset pulse is also generated at power-on.
Manual Reset
The ability to initiate a reset via external logic or a manual
switch is provided in addition to the MIC2777’s automatic
supervisory functions. Typically, a momentary push-button
switch is connected such that IN is shorted to ground when
the switch contacts close. Assuming V
DD
and V
IN
are within
tolerance when the switch is released, the reset outputs will
be de-asserted no less than 140ms later. IN can also be driven
by an open-drain or open-collector logic signal.
November 2005
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MIC2777
嵌入式系统
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