MIC833
Micrel
MIC833
Comparator and Reference with Adj. Hystersis
Advance Information
General Description
The MIC833 is a micropower precision dual voltage com-
parator with an on-chip reference and latch.
High- and low-voltage thresholds are adjusted indepen-
dently, allowing for wide hysteresis. Three external resistors
determine the threshold voltages. Voltage detection thresh-
olds are accurate to 1%.
Supply current is extremely low (1µA, typical), making it ideal
for portable applications.
The MIC833 is supplied in Micrel’s IttyBitty™ 5-lead SOT-23-
5 package.
Features
• Optimized for PDAs, cellular telephones, pagers,
and other battery-powered devices
• Inputs and output can pulled up to 6V
regardless of supply voltage
• Independently adjustable high- and
low-voltage thresholds
• High
±1%
voltage threshold accuracy
• Extremely low 1µA typical supply current
• Immune to brief input transients
• 5-lead SOT-23 package
See the MIC2778 for applications requiring an output delay.
Applications
•
•
•
•
•
•
PDAs
Pagers
Cordless phones
Consumer electronics
Embedded controllers
Personal electronics
Ordering Information
Part Number
MIC833BM5
Marking
B11
Accuracy
1%
Temperature Range
–40°C to +85°C
Package
SOT-23-5
Typical Application
V
IN
V
DD
MIC833
R1
5
3
V
PULL-UP
4
R
PU
V
OUT
V
LTH
> V
HTH
V
REF
= 1.24V
V
LTH(max)
= V
HTH(max)
= 6V
V
PULL-UP(max)
= 6V
1.5V
≤
V
DD
≤
5.5V
VDD
LTH
HTH
OUT
GND
R2
1
2
R3
IttyBitty™ is a trademark of Micrel, Inc.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
January 2000
1
MIC833
MIC833
Micrel
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
DD
) ..................................... –0.3V to +7V
Input Voltages (V
LTH
, V
HTH
) .......................................... +7V
Output Current (I
OUT
) ................................................. 20mA
Storage Temperature (T
S
) ....................... –65°C to +150°C
ESD Rating,
Note 3
...................................................... 2kV
Operating Ratings
(Note 2)
Supply Voltage (V
DD
) .................................. +1.5V to +5.5V
Input Voltage (V
LTH
, V
HTH
) ............................ –0.3V to +6V
Ambient Temperature Range (T
A
) ............. –40°C to +85°C
Junction Temperature (T
J
) ....................... Internally Limited
Package Thermal Resistance (θ
JA
) ...................... 260°C/W
Electrical Characteristics
1.5V
≤
V
DD
≤
5.5V; T
A
= +25°C,
bold
values indicate –40°C
≤
T
A
≤
+85°C; unless noted
Symbol
I
DD
I
LTH,
I
HTH
V
REF
t
D
V
OUT
Parameter
Supply Current
Input Leakage Current
Reference Voltage
Propagation Delay
V
LTH
= 1.352V to 1.128V
V
HTH
= 1.128V to 1.352V
Output Voltage-Low,
Note 4
OUT de-asserted, I
SINK
= 1.6mA, V
DD
≥
1.6V
OUT de-asserted, I
SINK
= 100µA, V
DD
≥
1.2V
Note 1.
Note 2.
Note 3.
Note 4.
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
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 held low down to V
DD
= 1.2V.
Condition
outputs not asserted
Min
Typ
1
0.005
Max
2
10
1.252
Units
µA
nA
V
µs
µs
1.228
1.240
5
5
0.3
0.4
V
V
Functional Diagram
Note A
V
IN
(Note B)
V
LO
V
HI
Note A
V
PULL-UP
V
OUT
0V
Note A.
Brief transients are ignored by the MIC833. See “Applications Information.”
Note B.
V
LTH
> V
LO
>V
REF
.
Timing Diagram
V
REF
+ 100mV
Inputs
V
REF
V
REF
– 100mV
t
D
V
PULL-UP
V
OUT
0V
t
D
V
LTH
V
HTH
January 2000
3
MIC833
MIC833
Micrel
Block Diagram
V
DD
+1.5V to +5.5V
5
VDD
V
IN
Low-Voltage
Detect
LTH
V
LTH
3
R Q
High-Voltage
Detect
S Q
4
OUT
HTH
V
HTH
1
1.24V
Bandgap
Reference
MIC833
2
GND
Functional Description
The MIC833 monitors a voltage and detects when it is below
or above two independently programmed levels.
Voltage Low Output
The output (OUT) is an active-high, open-drain output which
sinks current when the MIC833 detects a low input voltage at
its LTH input. This condition is latched until the HTH input is
presented with a voltage higher than the internal V
REF
(+1.24V).
Trip Points
Input voltage is monitored by the comparators via a voltage
divider network. The divided voltage is compared to an
internal reference voltage. When the voltage at the LTH input
pin drops below the internal reference voltage, the output
pulls low. Because of the voltage divider, the voltage at HTH
is assured to be below the reference voltage.
MIC833
4
January 2000
MIC833
Micrel
drain to 3.1V. Using 3.1V for the V
IN(lo)
threshold allows
calculation of the two remaining resistor values.
1M
Ω
V
IN(lo)
=
3.1V
=
1.24
R2
+
344k
Applications Information
Output
Since the MIC833 output is an open-drain MOSFET, most
applications will require a pull-up resistor. The value of the
resistor should not be too large or leakage effects may
dominate. 470kΩ is the maximum recommended value. Note
that the output may be pulled up as high as 6V regardless of
IC supply voltage. See “Electrical Characteristics.”
Programming the Thresholds
The low-voltage threshold is calculated using:
R1
+
R2
+
R3
V
IN(lo)
=
V
REF
R2
+
R3
The high-voltage threshold is calculated using:
R1
+
R2
+
R3
V
IN(hi)
=
V
REF
R3
where, for both equations:
R2
=
56k
Ω
1M
Ω −
(
R2
−
R3
)
=
R1
R1
=
600k
Ω
The accuracy of the resistors can be chosen based upon the
accuracy required by the system.
The inputs may be subjected to voltages as high as 6V steady
state without adverse effects of any kind, regardless of the IC
supply voltage. This applys even if the supply voltage is zero.
This permits the situation in which the IC supply is turned off,
but voltage is still present on the inputs. See “Electrical
Characteritics.”
Input Transients
The MIC833 is inherently immune to very short negative-
going “glitches.” Very brief transients may exceed the V
IN(lo)
threshold without tripping the output.
As shown in Figure 2, the narrower the transient, the deeper
the threshold overdrive that will be ignored by the MIC833.
The graph represents the typical allowable transient duration
for a given amount of threshold overdrive that will not toggle
the output.
MAX. TRANSIENT DURATION (µs)
140
120
100
80
60
40
20
0
1
10
100
1000
V
REF
=
1.240V
In order to provide the additional criteria needed to solve for
the resistor values, the resistors can be selected such that
they have a given total value, that is, R1 + R2 + R3 = R
TOTAL
.
A value such as 1MΩ for R
TOTAL
is a reasonable value
because it draws minimum current but has no significant
effect on accuracy.
When working with large resistors, a small amount of leakage
current can cause voltage offsets that degrade system accu-
racy. The maximum recommended total resistance from V
IN
to ground is 3MΩ.
V
IN
V
DD
Input Transient
Response
R1
604k
1%
56k
1%
340k
1%
MIC833
5
3
1
VDD
LTH
HTH
OUT
GND
4
470k
V
OUT
2
R2
R3
RESET COMP. OVERDRIVE, V
REF
–V
LTH
(mV)
Figure 2. Input Transient Response
Figure 1. Example Circuit
Once the desired trip points are determined, set the V
IN(hi)
threshold first.
For example, use a total of 1MΩ = R1 + R2 + R3. For a typical
single-cell lithium ion battery, 3.6V is a good “high threshold”
because at 3.6V the battery is moderately charged. Solving
for R3:
1M
Ω
V
IN(hi)
=
3.6V
=
1.24
R3
R3
=
344k
Ω
Once R3 is determined, the equation for V
IN(lo)
can be used
to determine R2. A single lithium-ion cell, for example, should
not be discharged below 2.5V. Many applications limit the
Initialization Behavior
When the MIC833 is powered up, the comparators and latch
become active before the reference voltage reaches its final
value. In most applications, this presents no problems. How-
ever, the user should be aware of this: when applying power
to the part, if the input voltage is
between
the two thresholds,
the output of the part will be
high
because input HTH will have
been higher than the 1.24V reference during initialization.
It is not very likely the part would be powered up in this state;
it is more likely the same power supply will power the part and
develop its inputs. However, if the above-described condition
should occur, the next HTH threshold crossing would
not
be
processed; that is, the latch would have been already set. The
next valid input condition would have to be a crossing of the
LTH threshold, which resets the latch, after which “normal”
operation is restored.
January 2000
5
MIC833
嵌入式系统
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