MIC2776 Datasheet by Microchip Technology

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MIC2776 IIIlllilEl.® MICROPROCESSOR November 2005 ’l MIC2776
November 2005 1 MIC2776
MIC2776 Micrel, Inc.
MIC2776
Micro-Power Low Voltage Supervisor
General Description
The MIC2776 is a power supply supervisor which provides
under-voltage monitoring and power-on reset generation in a
compact 5-pin SOT package. Features include an adjustable
under-voltage detector, a delay-generator, a manual reset
input, and a choice of active-high, active-low, or open-drain
active-low reset output. The user-adjustable monitoring input
is compared against a 300mV reference. This low reference
voltage allows monitoring voltages lower than those supported
by previous supervisor ICs.
The reset output is asserted for no less than 140ms at power-
on and any time the input voltage drops below the reference
voltage. It remains asserted for the timeout period after the
input voltage subsequently rises back above the threshold
boundary. A reset can be generated at any time by asserting
the manual reset input, /MR. The reset output will remain ac-
tive at least 140ms after the release of /MR. The /MR input
can also be used to daisy-chain the MIC2776 onto existing
power monitoring circuitry or other supervisors. Hysteresis
is included to prevent chattering due to noise. Typical supply
current is a low 3.0µA.
Typical Application
IN
/RST
VDD
/MR GND
MIC2776L
R1
R2
/RESET
VCORE
GND
Power_Good
VCORE 1.0V
Manual
Reset
MICROPROCESSOR
VI/O
VI/O 2.5V
Features
User-adjustable input can monitor supplies as low as
0.3V
±1.5% threshold accuracy
Separate VDD input
Generates power-on reset pulse (140ms min.)
Manual reset input
Choice of active-high, active-low or open-drain active-
low reset output
Inputs can be pulled above VDD (7V abs. max.)
Open-drain output can be pulled above VDD (7V abs.
max.)
Ultra-low supply current, 3.0µA typical
Rejects brief input transients
IttyBitty™ SOT-23-5 package
Applications
Monitoring processor, ASIC, or FPGA core voltage
Computer systems
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.
MIC2776 Micrel, Inc
MIC2776 2 November 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
Pin Description
Pin Number Pin Number Pin Name Pin Function
MIC2776H MIC2776L
MIC2776N
1 RST Digital (Output): Asserted high whenever VIN falls below the reference volt-
age. It will remain asserted for no less than 140ms after VIN returns above
the threshold limit.
1 /RST Digital (Output): Asserted low whenever VIN falls below the reference volt-
age. It will remain asserted for no less than 140ms after VIN returns above
the threshold limit. (open-drain for “N” version)
2 2 GND Ground
3 3 /MR Digital (Input): Driving this pin low initiates an immediate and unconditional
reset. Assuming IN is above the threshold 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): Independent supply input for internal circuitry.
Ordering Information
Part Number Reset Output Temperature Range Package
Standard Marking Pb-Free Marking
MIC2776N-BM5 UKAA MIC2776N-YM5 UKAA Open-Drain, Active-Low / RST –40ºC to +85ºC SOT-23-5
MIC2776H-BM5 ULAA MIC2776H-YM5 ULAA Active-High, Complementary RST –40ºC to +85ºC SOT-23-5
MIC2776L-BM5 UMAA MIC2776L-YM5 UMAA Active-Low, Complementary /RST –40ºC to +85ºC SOT-23-5
UTP November 2005 3 M|02776
November 2005 3 MIC2776
MIC2776 Micrel, Inc.
Absolute Maximum Ratings (Note 1)
Supply Voltage (VDD) .......................................–0.3V to +7V
Input Voltages (VIN, V/MR) ...............................–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
VDD = 3.3V; 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 = 3.3V; /MR, RST, /RST open 3.0 µA
IN, UNDER-VOLTAGE DETECTOR INPUT
VREF Under-Voltage Threshold TA = 25°C 295 300 305 mV
VHYST Hysteresis Voltage 3 mv
IIN Input Current 5 pA
TMIN ≤ TA ≤ TMAX 10 nA
RESET OUTPUTS (/RST, RST)
tPROP Propagation Delay VIN = (VREF(MAX) + 100mV) to 20 µs
VIN = (VREF(MIN) – 100mV)
tRST Reset Pulse Width 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
MANUAL RESET INPUTS (/MR)
VIH Input High Voltage 1.5V ≤ VDD ≤ 5.5V 0.7VDD V
VIL Input Low Voltage 1.5V ≤ VDD ≤ 5.5V 0.3VDD V
tPROP Propagation Delay V/MR < VIL 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.
MIC2776 Micrel, Inc
MIC2776 4 November 2005
Timing Diagram
VOH
VOL
V/MR
VIN
VDD
0V
0V
VOH
VOL
tRST
tRST
V/RST
tRST
tRST
VOH
VOL
VRST
>tmin
A
AVHYST
VREF
Propagation delays not shown for clarity.
Note A. The MIC2776 ignores very brief transients.
See “Applications Information” for details.
iagram V ' Pmoul and po‘amy vary by :19 See ordenng mlormallon table. November 2005 5 M|02776
November 2005 5 MIC2776
MIC2776 Micrel, Inc.
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 chat-
tering due to noise.
RST, /RST Reset Output
Typically, the MIC2776 is used to monitor the power supply
of intelligent circuits such as microcontrollers and micropro-
cessors. By connecting the reset output of a MIC2776 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 condi-
tions. In addition, asserting /MR, the manual reset input, will
activate the reset function.
Functional Diagram
R
S
Q
/Q
/MR
IN
MIC2776
* Pinout and polarity vary by device type.
See ordering information table.
VDD
/RST*
RST*
VREF
GND
Delay
One Shot
IPU
The reset outputs are asserted any time /MR is asserted or
if VIN drops below the threshold voltage. The reset outputs
remain asserted for tRST(min) after VIN subsequently returns
above the threshold boundary and /MR is released. A reset
pulse is also generated at power-on.
/MR, Manual Reset Input
The ability to initiate a reset via external logic or a manual
switch is provided in addition to the MIC2776’s automatic
supervisory functions. Driving the /MR input to a logic low
causes an immediate and unconditional reset to occur. As-
suming VIN is 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 con-
nected such that /MR is shorted to ground when the switch
contacts close. The switch may be connected directly between
/MR and GND. /MR has an internal 100nA pull-up current to
VDD and may be left open if unused.
V 1.025 1.025
MIC2776 Micrel, Inc
MIC2776 6 November 2005
Application Information
Programming the Voltage Threshold
Referring to the “Typical Application Circuit”, the voltage
threshold 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 = RTOTAL – R2
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, VCORE, in
this example is 1.0V ±5%. The main power rail and I/O volt-
age, VI/O, is 2.5V ±5%. As shown in Figure 1, the MIC2776
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 MIC2776’s power 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 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.
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 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:
VERROR = IIN(max) × (R1||R2) =
VERROR = ±1 × 10-8A × 2.189 ×105Ω =
VERROR = ±2.189 × 10-3V =
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 the
resistors, simply reduce the value of RTOTAL to minimize
offset errors.
Vcon M‘CROPROCESSOR M‘CROPROCESSOR D17 17 M‘CROPROCESSOR 17 7 Typical INPUT MAX TRANS‘ENT DURA'HON (us) November 2005 7 M|02776
November 2005 7 MIC2776
MIC2776 Micrel, Inc.
IN
/RST
VDD
/MR GND
MIC2776
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. MIC2776 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 MIC2776N’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
MIC2776N
R1
R2
/RESET
VCC
GND
VCC
MICROPROCESSOR
100k
Figure 2. Interfacing to Bidirectional Reset Pin
Transient Response
The MIC2776 is inherently immune to very short negative-
going “glitches.” Very brief transients may exceed the voltage
threshold without tripping the output.
As shown in Figure 3, the narrower the transient, the deeper the
threshold overdrive that will be ignored by the MIC2776. The
graph represents 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
RESET COMP. OVERDRIVE, VREF–VIN (mV)
Typical INPUT
Transient Response
Figure 3. Typical INPUT Transient Response
Ensuring Proper Operation at Low Supply
At levels of VDD below 1.2V, the MIC2776L’s /RST output
driver cannot turn on sufficiently to produce a valid logic-low
on the /RST output. In this situation, other circuits driven by
/RST could be allowed to float, causing undesired opera-
tion. (In most cases, however, it is expected that the circuits
driven by the MIC2776L 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 resis-
tor to the /RST output. A value of 100kΩ is recommended as
this is usually an acceptable compromise of leakage current
and pull-down current. The resistor’s value is not critical,
however. See Figure 4.
The statements above also apply to the MIC2776H’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
MIC2776L
R1
R2
/RESET
VCC
GND
V
CC
Manual
Reset
MICROPROCESSOR
100k
Rpull-down
Figure 4. MIC2776L Valid /Reset Below 1.2V
IN
RST
VDD
/MR GND
MIC2776H
R1
R2
RESET
VCC
GND
VCC
Manual
Reset
MICROPROCESSOR
100k
Rpull-up
Figure 5. MIC2776H Valid Reset Below 1.2V
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MIC2776 Micrel, Inc
MIC2776 8 November 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.
© 2000 Micrel, Inc.

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