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LTC1042 Window Comparator
FEATURES

DESCRIPTIO

Micropower 1.5W (1 Sample/Second) Wide Supply Range -- 2.8V to 16V High Accuracy Center Error 1mV Max Width Error 0.15% Max Wide Input Voltage Range V+ to Ground TTL Outputs with 5V Supply Two Independent Ground-Referred Control Inputs Small Size 8-Pin MiniDIP
The LTC(R)1042 is a monolithic CMOS window comparator manufactured using Linear Technology's enhanced LTCMOSTM silicon gate process. Two high impedance voltage inputs, CENTER and WIDTH/2, define the middle and width of the comparison window. Whenever the input voltage, VIN, is inside the window the WITHIN WINDOW output is high. The ABOVE WINDOW output is high whenever VIN is above the window. By interchanging VIN and CENTER, the ABOVE WINDOW output becomes BELOW WINDOW and is high if VIN is below the window. Sampling techniques provide high impedance voltage inputs that can common mode to both supply rails (V+ and GND). An important feature of the inputs is their non-interaction. Also the device is effectively "chopper stabilized," giving it extremely high accuracy over all conditions of temperature, power supply and input voltage range. Another benefit of the sampling techniques used to design the LTC1042 is the extremely low power consumption. When the device is strobed, it internally turns on the power to the comparators, samples the inputs, stores the outputs in CMOS latches and then turns off power to the comparators. This all happens in about 80s. Average power can be made small, almost arbitrarily, by lowering the strobe rate. The device can be self-strobed using an external RC network or strobed externally by driving the OSC pin with a CMOS gate.
APPLICATIO S

Fault Detectors Go/No-Go Testing Microprocessor Power Supply Monitor
, LTC and LT are registered trademarks of Linear Technology Corporation. LTCMOS is a trademark of Linear Technology Corp.
TYPICAL APPLICATIO
V+
Battery-Powered Remote Freezer Alarm
10000
150k 150k 1 2 3 3V TO 16V R1* 7.5k T 4 LTC1042 8 7 6 5 0.05F R2* 576
Total Supply Current vs Sampling Frequency
V+ = 6V
TOTAL SUPPLY CURRENT, IT (A)
IT
"HI" = TEMPERATURE BETWEEN 10M 5% 26F AND 31F 1F "HI" = TEMPERATURE ABOVE 31F 1F
1000 IT 100 10 LTC1042 SUPPLY CURRENT 1 0.1 0.01 FOR THIS APPLICATION fS 1HZ 0.1 1 10 100 1000 SAMPLING FREQUENCY, fS (Hz) 10000
T = YELLOW SPRINGS INSTRUMENT CO., INC. P/N 44007 ALL RESISTORS 1% UNLESS OTHERWISE SPECIFIED *OTHER TEMPERATURE BANDS MAY BE SELECTED BY CHOOSING APPROPRIATE VALUES FOR R1 AND R2
LTC1042 * A01
U
LTC1042 * TA02
U
U
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LTC1042
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW WITHIN WINDOW 1 CENTER 2 VIN GND 3 4 8 7 6 5 V+ OSC ABOVE WINDOW WIDTH / 2
Total Supply Voltage (V+ to GND) ............................ 18V Input Voltage ..................................... V+ +0.3V to -0.3V Operating Temperature Range LTC1042C ......................................... -40C to 85C LTC1042M (OBSOLETE) ................. -55C to 125C Storage Temperature Range ................. -55C to 150C Lead Temperature (Soldering, 10 sec).................. 300C Output Short Circuit Duration ....................... Continuous
ORDER PART NUMBER LTC1042CN8
N8 PACKAGE 8-LEAD PDIP TJMAX = 110C, JA = 150C/W J8 PACKAGE 8-LEAD CERDIP
LTC1042MJ8
OBSOLETE PACKAGE
Consider the N8 Package as an Alternate Source
LTC1042 * POI01
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Center Error (Note 3) TEST CONDITIONS V+
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C.
MIN
TYP 0.3 + 0.05 1 + 0.05 0.6 + 0.1 2 + 0.1 0.3
MAX 1 + 0.15 3 + 0.15 2 + 0.3 6 + 0.3
UNITS mV % WIDTH/2 mV % WIDTH/2 mV % WIDTH/2 mV % WIDTH/2 nA M
= 2.8V to 6V (Note 2)
V+
= 6V to 15V (Note 2)
Width Error (Note 4)
V + = 2.8V to 6V (Note 2)
V + = 6V to 15V (Note 2)
IBIAS RIN
Input Bias Current Average lnput Resistance Input Voltage Range
V + = 5V, TA = 25C, OSC = GND VIN, CENTER and WIDTH/2 Inputs fS = 1kHz (Note 5)

10 GND 2.8
15 V+ 16 1.2 0.001 0.001 80 3 0.5 5.0 100
PSR IS(ON) IS(OFF) TD VOH VOL
Power Supply Range Power Supply ON Current (Note 6) Power Supply OFF Current (Note 6) Response Time (Note 7) Output Levels Logic 1 Output Logical 0 Output V+ = 5V V+ = 5V, LTC1042C LTC1042M V+ = 5V V+ = 4.75V, lOUT = -360A V+ = 4.75V, lOUT = -1.6mA

2.4
4.4 0.25
0.45
2
U
V V mA A A s V V
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WW
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LTC1042
ELECTRICAL CHARACTERISTICS
SYMBOL REXT fS PARAMETER External Timing Resistor Sampling Frequency TEST CONDITIONS
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C.
MIN
TYP
MAX 10,000
UNITS k Hz
Resistor connected between V + and OSC Pin V + = 5V, TA = 25C REXT =1M, CEXT = 0.1F
100 5
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Applies over input voltage range limit and includes gain uncertainty. Note 3: Center error = [(VU +VL)/2 - CENTER] (where VU = upper band limit and VL = lower band limit).
Note 4: Width error = (VU -VL - 2 * WIDTH/2) (where VU = upper band limit and VL = lower band limit). Note 5: RIN is guaranteed by design and is not tested. RIN = 1/(fS x 66pF). Note 6: Average supply current = TD * lS(ON) * fS + (1 - TD fS) IS(OFF). Note 7: Response time is set by an internal oscillator and is independent of overdrive voltage. TD is guaranteed by correlation test and is not directly measured.
TYPICAL PERFOR A CE CHARACTERISTICS
IS(ON) vs V+
20
NORMALIZED SAMPLING FREQUENCY (fS AT 5V, 25C)
18 16 14
TA = 125C 1.6 1.4 1.2 1.0 0.8 0.6 TA = - 55C 0 2 8 10 12 4 6 SUPPLY VOLTAGE, V+ (V) 14 16 TA = 25C
SAMPLE RATE, fS (Hz)
IS(ON) (mA)
12 10 8 6 4 2 0 2 4 10 8 6 12 SUPPLY VOLTAGE, V+ (V) 125C -55C
Response Time vs Supply Voltage
110 TA = 25C 100
130 120
V+ = 5V
RESPONSE TIME, tD (s)
RESPONSE TIME, t D (s)
110 100 90 80 70 60 50
AVERAGE INPUT RESISTANCE, RIN (1/FS * 66pF) ()
90 80 70 60 50 2 4 10 14 8 12 6 SUPPLY VOLTAGE, V+ (V) 16
UW
25C 14
Normalized Sampling Frequency vs V+, Temperature
2.2 2.0 1.8 R = 1M, C = 0.1F
Sampling Rate vs REXT CEXT
103 CEXT = 1000pF 102 CEXT = 0.01F 10 CEXT = 0.1F 1 CEXT = 1F 0.1 100k CEXT = 0.05F
16
1M R EXT ()
10M
LTC1042 * TPC03
LTC1042 * TPC01
LTC1042 * TPC02
Response Time vs Temperature
1011
RIN vs Sampling Frequency
1010
109
108
40 -50
107 1
0 25 -25 50 75 100 AMBIENT TEMPERATURE, TA (C)
125
10 102 103 SAMPLING FREQUENCY, fS (Hz)
104
LTC1042 * TPC04
LTC1042 * TPC05
LTC1042 * TPC06
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LTC1042
APPLICATIO S I FOR ATIO
The LTC1042 uses sampled data techniques to achieve its unique characteristics. It consists of two comparators, each of which has two differential inputs (Figure 1). When the sum of the voltages on a comparator's inputs is positive, the output is high; when the sum is negative, the output is low. The inputs are interconnected such that when (CENTER - WIDTH/2) VIN (CENTER + WIDTH/2) both comparator outputs are low. In this condition VIN is within the window and the WITHIN WINDOW output is high. When VIN > CENTER + WIDTH/2, VIN is above the window and the ABOVE WINDOW output is high. An important feature of the LTC1042 is the non-interaction of the inputs. This means the center and width of the window can be changed without one affecting the other. Also note that the width of the window is set by a ground referred signal WlDTH/2). Strobing An internal oscillator allows the LTC1042 to strobe itself. The frequency of oscillation sets the sampling rate and is set with an external RC network (see typical curve, OSC frequency vs REXT, CEXT). To assure oscillation, under all conditions, REXT must be between 100k and 10M. There is no limit to the size of CEXT. A sampling cycle is initiated on the positive going transition of the voltage on the OSC pin. When this voltage is near the positive supply, a Schmitt trigger trips and initiates the sampling cycle. A sampling cycle consists of applying power to both comparators, sampling the inputs,
WINDOW CENTER (VIN) 2
+ - + - + - + -
COMP A 4 WINDOW CENTER V+ WITHIN WINDOW ABOVE WINDOW
VIN (WINDOW CENTER) WIDTH/2
1 WITHIN WINDOW 3 ABOVE WINDOW (BELOW WINDOW)
COMP B
6
5
OUTPUT VOLTAGE (V)
GND
4 TIMING GENERATOR
4 0V POWER ON VL INPUT VOLTAGE, VIN POWER OFF 80s VU
OSC
7
(A) Figure 1. LTC1042 Block Diagram
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storing the results in CMOS output latches and turning the power off. This whole process takes approximately 80s. During the 80s "active" time, the LTC1042 draws typically 1.2mA (lS(ON)) at V + = 5V. Because power is consumed only during the "active" time, extremely low average power consumption can be achieved at low sample rates. For example, at a sample rate of 1 sample/second the average power consumption is: Power = (V+) (IS(AVG)) = 5V * 1.2mA * 80s/1sec = 0.48W At low sampling rates, REXT dominates the power consumption. REXT consumes power continuously. The average voltage at the OSC pin is approximately V+/2. The power consumed by REXT is: P(REXT) = (V+/2)2REXT Example: Assume REXT = 1M and V+ = 5V. Then: P(REXT) = (2.5)2/1M = 6.25W This is more than ten times the typical power consumed by the LTC1042 at V+ = 5V and 1 sample/second. Where power is a premium, REXT should be made as large as possible. Note that the power dissipated by REXT is not a function of the sampling frequency or CEXT. If high sampling rates are needed and power consumption is of secondary importance, a convenient way to get the maximum possible sampling rate is to make REXT = 100k and CEXT = 0. The sampling rate, set by the LTC1042's active time, will nominally be 10kHz.
8 V+ -WIDTH/2 WIDTH/2
W
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(B)
LTC1042 * AI01
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LTC1042
APPLICATIO S I FOR ATIO
To synchronize the sampling of the LTC1042 to an external frequency source, the OSC pin can be driven by a CMOS gate. A CMOS gate is necessary because the input trip points of the oscillator are close to the supply rails and TTL does not have enough output swing. Externally driven, there will be a delay from the rising edge of the OSC input and the start of the sampling cycle of approximately 5s. Input Impedance The input impedance of the LTC1042 does not look like a classic linear comparator; CMOS switches and a precision capacitor array form the dual differential input structure. Input impedance characteristics can be determined from the equivalent circuit shown in Figure 2. The input capacitance will charge with a time constant of RS * CIN. It is critical, in determining errors caused by the input charging current, that CIN be fully charged during the "active" time. For RS 10k For Rs less than or equal to 10k, CIN fully charges and no error is caused by the charging current. For RS > 10k For source resistances greater than 10k, CIN cannot fully charge, causing voltage errors. To minimize these errors an input bypass capacitor, CS should be used. Charge is shared between CIN and CS causing a voltage error. The magnitude of this error is V = VIN x CIN/(CIN + CS). This error can be made arbitrarily small by increasing CS. The averaging effect of the bypass capacitor CS causes another error term. Each time the input switches cycle between the plus and minus inputs, CIN is charged and discharged. The average input current due to this is
RS VIN CS
Figure 2. Equivalent Input Circuit
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lAVG = VIN x CIN x fS, where fS is the sampling frequency. Because the input current is directly proportional to the differential input voltage, the LTC1042 can be said to have an average input resistance of RIN = VIN/IAVG = 1/(fS x CIN). Since two comparator inputs are connected in parallel, RIN is one half this value (see typical curve of RIN vs Sampling Frequency). This finite input resistance causes an error due to voltage divided between RS and RIN. The input error caused by both of these effects is VERROR = VIN[2CIN/(2CIN + CS) + RS/(RS + RIN)]. EXAMPLE: Assume fS = 10Hz, RS = 1M, CS = 1F and VIN = 1V. Then VERROR = 1V(66V + 660V) = 726V. If the sampling frequency is reduced to 1Hz, the voltage error from input impedance effects is reduced to 136V. Input Voltage Range The input switches of the LTC1042 are capable of switching either to the V+ supply or ground. Consequently, the input voltage range includes both supply rails. This is a further benefit of the input sampling structure. Error Specifications The only measurable errors on the LTC1042 are the deviations from "ideal" of the upper and lower window limits [Figure 1(B)]. The critical parameters for a window comparator are the width and center of the window. These errors may be expressed in terms of VU and VL. center error = [(VU + VL)/2] - CENTER width error = (VU - VL) - 2 x (WIDTH/2) The specified error limits (see Electrical Characteristics) include error due to offset, power supply variation, gain, time and temperature.
CIN ~ (~33pF) S1
W
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+
S2
-
V- LTC1042 DIFFERENTIAL INPUT
LTC1042 * AI02
5
LTC1042
APPLICATIO S I FOR ATIO
TTL Power Supply Monitor
TTL SUPPLY V+
V+
25k
10k 0.25%
LT1004-2.5
10k 0.25%
ALL RESISTORS 5% UNLESS OTHERWISE NOTED * SUPPLY TOLERANCE EQUALS R2 IN k. I.E., 10k = 10%
Single 5V Thermocouple Over Temperature Alarm
COLD JUNCTION COMPENSATOR 36k 5% TTL SUPPLY V+ 5V
R4 5k AT 25C R1** 1690 LT1034-1.2 7 187 1820 4 1/2 LTC1043 8 3 7 LTC1052N8 11 1F 12 13 THERMOCOUPLE TYPE J K T S R4 232k 301k 301k 2.1M 16 17 VCENTER = 0.0047F 1.235 * (R2 + R3) R1 + R2 + R3 1.235 * R3 R1 + R2 + R3 14 RI* R3** 1F 0.1F 2 1 4 0.1F RF** 8 CF* R2**
LTC1042 * A104
+
VT 1k
-
6
U
1 2 3 4 LTC1042 8 7 6 5 R2* 10k "HI" = ABOVE RANGE (V + > 5.5V) 100k 100k "HI" = SUPPLY IN RANGE (4.5 < V+ < 5.5)
LTC1042 * AI03
W
UU
VT 1+ 6
(
RF RI
)
1 2 3 4 LTC1042
8 7 6 5 100k 5%
TEMPERATURE IN WINDOW
TEMPERATURE HIGH
WIDTH = 2 *
YELLOW SPRINGS INST. CO. P/N 44007 * CHOOSE CF TO FILTER NOISE ** CHOOSE RF, RI, R1, R2 AND R3 TO SET WINDOW ALL RESISTORS 1% UNLESS OTHERWISE NOTED
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LTC1042
APPLICATIO S I FOR ATIO
Wind Powered Battery Charger
A simple wind powered battery charger can be constructed using the new LTC1042, a 12V DC permanent magnet motor, and low cost power FET transistor. The DC motor is used as a generator with the voltage output being proportional to its RPM. The LTC1042 monitors the voltage output and provides the following control functions: 1) If generator voltage output is below 13.8V, the control circuit is active and the NiCad battery is charging through the LM334 current source. The lead acid battery is not being charged.
WIND
12V GENERATOR
LM334 68 0.1F
215k 4.5V NiCAD BATTERY 10k
100k
LT1004-1.2
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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2) If the generator voltage output is between 13.8V and 15.1V, the 12V lead acid battery is being charged at about a 1A/hour rate (limited by the power FET). 3) If generator voltage exceeds 15.1V (a condition caused by excessive wind speed or 12V battery being fully charged) then a fixed load is connected thus limiting the generator RPM to prevent damage. This charger can be used as a remote source of power where wind energy is plentiful, such as on sailboats or remote radio repeater sites. Unlike solar powered panels, this system will function in bad weather and at night.
107k 1N4001 10k 0.1F
W
UU
+
WITHIN WINDOW 13.8V TO 15.1V 12V LEAD ACID 36 5W MTP8N05
1 2 3 4 LTC1042
8 7 6 5
10M
+
0.1F
OVER VOLTAGE (>15.1V)
MTP8N05
LTC1042 * A105
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LTC1042
PACKAGE DESCRIPTIO U
J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic)
(Reference LTC DWG # 05-08-1110)
.200 (5.080) MAX .015 - .060 (0.381 - 1.524) .005 (0.127) MIN .405 (10.287) MAX 8 7 6 5 .023 - .045 (0.584 - 1.143) HALF LEAD OPTION .045 - .068 (1.143 - 1.650) FULL LEAD OPTION .025 (0.635) RAD TYP 1 .045 - .065 (1.143 - 1.651) .014 - .026 (0.360 - 0.660) .100 (2.54) BSC .125 3.175 MIN
J8 0801
.300 BSC (7.62 BSC)
CORNER LEADS OPTION (4 PLCS)
.220 - .310 (5.588 - 7.874)
.008 - .018 (0.203 - 0.457)
0 - 15
2
3
4
NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS
OBSOLETE PACKAGE
N8 Package 8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
.400* (10.160) MAX 8 7 6 5
.255 .015* (6.477 0.381)
1 .300 - .325 (7.620 - 8.255)
2
3
4 .130 .005 (3.302 0.127)
.045 - .065 (1.143 - 1.651)
.008 - .015 (0.203 - 0.381) +.035 .325 -.015 +0.889 8.255 -0.381
.065 (1.651) TYP .120 (3.048) .020 MIN (0.508) MIN .018 .003 (0.457 0.076)
N8 1002
(
)
.100 (2.54) BSC
INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
NOTE: 1. DIMENSIONS ARE
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LW/TP 1202 1K REV A * PRINTED IN USA
www.linear.com
LINEAR TECHNOLOGY CORPORATION 1988

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