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MIC833
Micrel
MIC833
Comparator and Reference with Adj. Hystersis Final Information
General Description
The MIC833 is a micropower precision dual voltage comparator with an on-chip reference and latch. High- and low-voltage thresholds are adjusted independently, allowing for wide hysteresis. Three external resistors determine the threshold voltages. Voltage detection thresholds are accurate to 1.5%. Supply current is extremely low (1A, typical), making it ideal for portable applications. The MIC833 is supplied in Micrel's IttyBittyTM 5-lead SOT-235 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 1.5% voltage threshold accuracy * Extremely low 1A 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 1.5% Temperature Range -40C to +85C Package SOT-23-5
Typical Application
VIN VDD MIC833 R1
5 3
VPULL-UP
4
RPU VOUT VLTH > VHTH VREF = 1.24V VLTH(max) = VHTH(max) = 6V VPULL-UP(max) = 6V 1.5V VDD 5.5V
VDD LTH HTH
OUT GND
R2
1
2
R3
IttyBittyTM 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
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MIC833
MIC833
Micrel
Pin Configuration
LTH GND HTH
3 2 1
4
5
OUT
VDD
SOT-23-5 (M5)
Pin Description
Pin Number 1 Pin Name HTH Pin Function High-Voltage Threshold (Input): Analog input to a comparator. This is the voltage input assigned to detect a high-voltage condition when the level on this pin exceeds VREF, OUT is asserted and the condition is latched until VLTH < VREF. Ground Low-Voltage Threshold (Input): Analog input to a comparator. This is the voltage input assigned to detect a low voltage condition. When the level on this pin falls below VREF, OUT is de-asserted and the condition is latched until VHTH > VREF. Output: Active-high, open-drain output. This output is de-asserted and latched when VLTH VREF. Power Supply (Input): Independent supply input for internal circuitry.
2 3
GND LTH
4
OUT
5
VDD
MIC833
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Absolute Maximum Ratings (Note 1)
Supply Voltage (VDD) ..................................... -0.3V to +7V Input Voltages (VLTH, VHTH) .......................................... +7V Output Current (IOUT) ................................................. 20mA Storage Temperature (TS) ....................... -65C to +150C ESD Rating, Note 3 ...................................................... 2kV
Operating Ratings (Note 2)
Supply Voltage (VDD) .................................. +1.5V to +5.5V Input Voltage (VLTH, VHTH) ............................ -0.3V to +6V Ambient Temperature Range (TA) ............. -40C to +85C Junction Temperature (TJ) ....................... Internally Limited Package Thermal Resistance (JA) ...................... 260C/W
Electrical Characteristics
1.5V VDD 5.5V; TA = +25C, bold values indicate -40C TA +85C; unless noted Symbol IDD ILTH, IHTH VREF tD VOUT Parameter Supply Current Input Leakage Current Reference Voltage Propagation Delay VLTH = 1.352V to 1.128V VHTH = 1.128V to 1.352V Output Voltage-Low, Note 4 OUT de-asserted, ISINK = 1.6mA, VDD 1.6V OUT de-asserted, ISINK = 100A, VDD 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. VDD operating range is 1.5V to 5.5V. output is guaranteed to be held low down to VDD = 1.2V.
Condition outputs not asserted
Min
Typ 1 0.005
Max 2 10 1.259
Units A nA V s s
1.221
1.240 5 5
0.3 0.4
V V
Functional Diagram
Note A VHI VIN VLO (Note B) Note A VPULL-UP VOUT 0V
Note A. Brief transients are ignored by the MIC833. See "Applications Information." Note B. VLTH > VLO >VREF.
Timing Diagram
VREF + 100mV Inputs VREF VREF - 100mV tD VPULL-UP VOUT 0V VLTH VHTH
tD
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MIC833
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Block Diagram
VDD +1.5V to +5.5V
5
VDD
VIN Low-Voltage Detect LTH VLTH
3
RQ High-Voltage Detect SQ
4
OUT
HTH VHTH
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 VREF (+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.
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drain to 3.1V. Using 3.1V for the VIN(lo) threshold allows calculation of the two remaining resistor values. 1M VIN(lo) = 3.1V = 1.24 R2 + 344k
R2 = 56k
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. 470k 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 VIN(lo) = VREF R2 + R3 The high-voltage threshold is calculated using: R1 + R2 + R3 VIN(hi) = VREF R3 where, for both equations:
1M - (R2 - R3) = R1
R1 = 600k 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 applies 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 negativegoing "glitches." Very brief transients may exceed the VIN(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 (s)
140 120 100 80 60 40 20 0 1 10 100 1000
VREF = 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 = RTOTAL. A value such as 1M for RTOTAL 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 accuracy. The maximum recommended total resistance from VIN to ground is 3M.
VIN VDD
Input Transient Response
R1
604k 1% 56k 1% 340k 1%
MIC833
5 3 1
VDD LTH HTH
OUT GND
4
470k VOUT
2
R2
R3
RESET COMP. OVERDRIVE, VREF-VLTH (mV)
Figure 2. Input Transient Response Figure 1. Example Circuit Once the desired trip points are determined, set the VIN(hi) threshold first. For example, use a total of 1M = 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: VIN(hi) 1M = 3.6V = 1.24 R3 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. However, 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.
R3 = 344k Once R3 is determined, the equation for VIN(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
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MIC833
MIC833
Example Application The battery charger of Figure 3 uses the MIC833 to detect a low-battery voltage condition (VDIS) and enables a constantcurrent source (ICHG). Charging current is enabled until a charged-battery voltage condition (VCHG) is detected; at which time the charging-current source is disabled. Diode D1 was added to Figure 3 to ensure the disabled current source does not draw battery current. Whether or not D1 is required is a function of the output stage of the current source and how it is disabled.
Charger Supply Voltage
Micrel
The circuitry of Figure 3 is deliberately generalized to imply flexibility of application. Depending on the application, it may not be possibly to power the MIC833 from the charger supply voltage, see Note 2. It may be necessary to provide a separate voltage regulator, or a resistive voltage divider to reduce the VDD applied to the MIC833. The part can be supplied by the battery voltage (VBAT) if this voltage is never lower than 1.5V, the minimum operating VDD of the part. Voltage thresholds, VDIS and VCHG, are programmed as described in the appropriate above paragraph.
Constant-Current Source Note 1 IN OUT D1 EN GND VDIS R2 VCHG R3
Note 2
R4 100k
VBATT (to load)
Battery
VDD LTH HTH
MIC833 OUT 0.1F GND
Note 1. D1 may not be required. It is shown here to indicate the disabled current source should not load the battery.
Note 2. VDD of the MIC833 is limited to 5.5V maximum. The part can be powered by VBAT if the battery is never discharged below VDD(min) = 1.5V
Figure 3. Battery Charger
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Package Information
1.90 (0.075) REF 0.95 (0.037) REF
1.75 (0.069) 1.50 (0.059)
3.00 (0.118) 2.60 (0.102)
DIMENSIONS: MM (INCH) 3.02 (0.119) 2.80 (0.110) 1.30 (0.051) 0.90 (0.035) 10 0 0.15 (0.006) 0.00 (0.000) 0.20 (0.008) 0.09 (0.004)
0.50 (0.020) 0.35 (0.014)
0.60 (0.024) 0.10 (0.004)
5-Pin SOT (M)
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MIC833
MIC833
Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. (c) 2001 Micrel Incorporated
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