LTC1531
Self-Powered Isolated
Comparator
FEATURES
s
s
s
s
s
s
s
DESCRIPTIO
UL Recognized File E151738 to UL1577
Self-Powered Across Isolation Barrier
2500V
RMS
Isolation
2.5V Isolated Reference, I
LOAD
= 5mA
MAX
Zero-Cross Output for Line Power
Dual Differential Input Comparator
High Input Impedance Comparator
APPLICATIO S
s
s
s
s
The LTC
®
1531 is an isolated self-powered dual differential
comparator. An internal capacitive isolation barrier pro-
vides 2500V
RMS
of isolation between the comparator and
its output. The part provides UL-rated isolated compari-
sons without the need for an isolated supply since both
comparator power and output data are transmitted across
the capacitive barrier. The comparator data is transferred
differentially across the isolation barrier to provide high
common mode voltage and noise immunity.
The isolated side can supply a 2.5V reference output to
power external sensor circuits such as a thermistor bridge.
The dual differential comparator inputs allow for compari-
son of two differential voltages as well as single-ended
voltages. The powered side provides a latched data output
as well as a pulsed zero-cross comparator output for
controlling a triac. The part is available in a 28-lead SO
package.
Self-Powered Isolated Sensing
Isolated Temperature Control
Isolated Voltage Monitor
Isolated Switch Control
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
Isolated Thermistor Temperature Controller
AC
120V
LOAD
25Ω
TECCOR
Q4008L4
OR EQUIVALENT
NEUTRAL
150Ω
1k
2N2222
1N4004
3k
3W
R1
680k
R2
47k
C1
0.01µF
ISOLATION
BARRIER
750Ω
0.5W
V
CC
ZCDATA
SHDN
ZCPOS
ZCNEG
+
100µF
DATA
+
Q D
–
+
DANGER!
LETHAL VOLTAGES
IN THIS SECTION!
–5.6V
20µF
50V
5.6V
390Ω
VALID
GND
LTC1531
ISOGND
1
LED
U
+
V
PW
2.5V
V
REG
V1
V2
V3
V4
CMPOUT
R5*1M
R6
22k
1
1
= ISOLATED GROUND
*HYSTERESIS = 1°C AT T
O
1
1531 TA01
U
U
R
THERM
=
R
O • e
B (1/T – 1/T
O
)
1µF
B = 3807
T
O
= 297°K
1
THERM
30k
YSI 44008
T
R4
50k
1
LTC1531
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
V
CC
SHDN
ZCNEG
ZCPOS
1
2
3
4
28 GND
27 ZCDATA
26 DATA
25 VALID
Total Supply Voltage (V
CC
to GND) ............................ 7V
Input Voltages
Isolated Comparator
(V1 to V4) .............................. – 0.3V to (V
PW
+ 0.3V)
SHDN, ZCPOS, ZCNEG ......................... – 0.3V to 12V
Current
Input Pins .......................................................
±10mA
ZCDATA, VALID, DATA ..................................
±10mA
Operating Temperature Range ..................... 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1531CSW
V
PW
11
CMPOUT 12
V
REG
13
ISOGND 14
18 V1
17 V2
16 V3
15 V4
SW PACKAGE
28-LEAD PLASTIC SO (ISO)
T
JMAX
= 125°C,
θ
JA
= 125°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C, V
CC
= 5V.
SYMBOL
I
VCC
V
ZCOS
V
HYS
f
SAMPLE
V
OS
R
VIN
I
VIN
V
REG
R
VREG
I
CMPOUT
t
VREG
V
PWH
I
VPW
V
ISO
PARAMETER
Supply Current
Zero-Cross Offset
Zero-Cross Hysteresis
Isolated Comparator Sample Rate
Isolated Comparator Offset
Isolated Comparator
Input Impedance
Isolated Comparator Input Current
V
REG
V
REG
Output Impedance
CMPOUT High Impedance Leakage Current
V
REG
On-Time
V
PW
, Power Detect Enable Voltage
Current Transfer to V
PW
Isolation Voltage
V
PW
= 0V
V
PW
= 3.3V
1 Minute (Note 6)
1 Second
q
q
CONDITIONS
SHDN = V
CC
, No Load
SHDN = 0V
V
CM
= V
CC
V
CM
= V
CC
(Note 7)
V
REG
Not Loaded (Note 2)
V1 = V2, V3 = V4
V1 – V3 = 2V, V4 – V2 = 2V
V1 = V3 = 2.5V, V2 = V4 = 0V
V1 = V2 = 1.25V, V3 = V4 = 0V
V1 = V3 – 2.5V, V2 = V4 = 0V
f
SAMPLE
= 700Hz (Note 4)
2mA Load V
PW
= 3.3V (Note 5)
2mA to 5mA Load
V
CMPOUT
= 2.5V
q
q
q
q
q
q
q
q
q
MIN
TYP
10
0.2
±30
200
300
2.0
2.0
18
300
±1
MAX
14
10
±120
800
4.0
4.0
UNITS
mA
µA
mV
mV
Hz
mV
mV
MΩ
MΩ
nA
2.40
2.50
4
1
2.55
15
130
90
108
3.3
45
30
2500
4500
2
U
W
U
U
W W
W
V
Ω
nA
µs
V
µA
µA
V
RMS
V
DC
LTC1531
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C, V
CC
= 5V.
SYMBOL
V
IH
V
IL
V
OH
V
OL
I
INL
, I
INH
dV/dt
C
ISO
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The sample rate is not continuous, but depends on V
PW
charging
rate. See Applications Information.
Note 3:
See Applications Information for further description of the
comparator switched-capacitor input circuit.
PARAMETER
SHDN Input High Voltage
SHDN Input Low Voltage
DATA, VALID, ZCDATA Output High Voltage
DATA, VALID, ZCDATA Output Low Voltage
SHDN Low or High Level Input Current
Continuous dV/dt Rejection
CONDITIONS
V
CC
= 4.5V
V
CC
= 5.5V
V
CC
= 4.5V, I
O
= – 400µA
V
CC
= 4.5V, I
O
= 1.6mA
V
IN
= 5V, 0V
(Note 8)
q
q
q
q
q
q
MIN
2.4
TYP
MAX
0.8
UNITS
V
V
V
V
µA
V/µs
pF
3.0
4.3
0.2
0.4
±1
50
70
2
Note 4:
The sample rate, f
SAMPLE
, varies with loading on V
PW
and V
REG
.
Note 5:
Load on CMPOUT pulls current from V
REG
when CMPOUT is high.
Note 6:
Value derived from 1 second test.
Note 7:
Zero-cross hysteresis is the minimum amount of signal amplitude
above or below 0V differential to retrigger the zero-cross comparator.
Note 8:
Parameter not tested but guaranteed by design.
TYPICAL PERFORMANCE CHARACTERISTICS
V
CC
= 5V, C
VPW
= 1µF
I
VREG
= 100µA, T
A
= 25°C
3.3
V
CC
= 5V
C
VPW
= 1µF
I
VREG
= 5mA
T
A
= 25°C
V
PW
V
RIPPLE
V
PW
(V)
V
REG
V
REG
(V)
0
0
2.5
0
100
TIME (ms)
NOTES: V
RIPPLE
DEPENDS ON C
VPW
AND I
VPW
+ I
VREG
t
SAMPLE
DEPENDS ON I
VPW
+ I
VREG
1531 F01
Figure 1. V
PW
Power-Up and
V
REG
Samples vs Time
U W
200
3.3
t
SAMPLE
2.5
300
10
20
30
TIME (ms)
40
NOTE: NONPERIODIC SAMPLES DUE TO DEPENDENCE
ON V
PW
> 3.3V AND THE POWER-LISTEN CYCLE
SAMPLING
1531 F02
Figure 2. V
REG
and V
PW
vs Time
(I
VREG
= 100µA)
3
LTC1531
TYPICAL PERFORMANCE CHARACTERISTICS
30
T
A
= 25°C
25
V
CC
= 4.5V
t
SAMPLE
(ms)
20
15
10
V
CC
= 5V
5
V
CC
= 5.5V
V
RMS
0
0
1
2
I
VREG
(mA)
Figure 3. Average t
SAMPLE
vs I
VREG
PIN FUNCTIONS
V
CC
(Pin 1):
Powered Side Power Supply.
SHDN (Pin 2):
Active Low Chip Shutdown. A low signal
causes the circuitry to power down. DATA logic output
level will be reset to zero during power-down.
ZCNEG (Pin 3):
Zero-Cross Comparator Negative Input.
ZCPOS (Pin 4):
Zero-Cross Comparator Positive Input.
V
PW
(Pin 11):
Isolated Power Supply. Connect to an
external storage capacitor.
CMPOUT (Pin 12):
Isolated Latched Comparator Data.
CMPOUT is active when V
REG
is on. The CMPOUT output
can be used on the isolated side for hysteresis (see
applications). The output will contain the result of the
previous comparison. When V
REG
is low, the CMPOUT pin
is Hi-Z.
V
REG
(Pin 13):
Isolated 2.5V Regulated Output. Pulsed on
for 100µs with a maximum load current of 5mA. V
REG
also
supplies power to the CMPOUT output (Pin 12).
ISOGND (Pin 14):
Isolated Side Power Ground.
V4 (Pin 15):
Comparator Negative Input. The comparator
inputs are summed together with the comparison output
equal to (V1 + V2)/2 > (V3 + V4)/2 or equivalently (V1 – V3)
> (V4 – V2).
V3 (Pin 16):
Comparator Negative Input.
V2 (Pin 17):
Comparator Positive Input.
V1 (Pin 18):
Comparator Positive Input.
VALID (Pin 25):
Pulsed Output. Indicates when valid data
was received from the comparator. May be used to clock
DATA to external circuitry.
DATA (Pin 26):
Latched Comparator Result. DATA holds
the value of the last valid comparison result. DATA changes
only when a valid comparison was received from the
isolated side.
ZCDATA (Pin 27):
A 24µs to 30µs Pulsed Output. The
pulse occurs when the DATA output is high and the zero-
cross comparator inputs (ZCPLS-ZCNEG) cross zero volts
differential. Typically the zero-cross input signal is an RC
phase shifted AC sine wave. This output is a TTL level pulse
that can be used for firing an external triac.
GND (Pin 28):
Power Supply Low Impedance Ground
Connection.
4
U W
4500V
BREAKDOWN
LIMIT
2500V
RMS
SLEW RATE = (π)(f)(V
P-P
)
450V
= (1.11)(f)(V
RMS)
50V/µs
= V
RMS
(1.11)(f)
45V
4.5V
450mV
3
4
1531 F03
10k
10M
100k
1M
FREQUENCY (Hz)
100M
1531 F04
Figure 4. V
RMS
vs Frequency
U
U
U
LTC1531
TI I G DIAGRA
W
POWER CYCLE
960µs
LISTEN CYCLE
192µs
200ns
POWER
V
REG
CMPOUT
Hi-Z
LISTEN
108µs
POWER-LISTEN CYCLE
1152µs
1531 TD01
BLOCK DIAGRAM
POWERED SIDE
V
CC
V
CC
1
VOLTAGE
PUMP
VALID 25
TIMING
DATA 26
Q D
R
POWER-ON
RESET
ZCDATA 27
CMPOUT
12
ZERO-CROSS
COMPARATOR
GND 28
W
UW
VALID
DATA
ISOLATION
BARRIER
V
PW
11
3.3V
DET
ISOLATED SIDE
V1
18
TRANSMIT
AND
DRIVER
+
LATCH
COMPARE
Σ
Σ
V2
17
V3
16
V4
15
V
REG
13
–
+
TIMING
DECODE
–
2.5V
REG
4
3
2
SHDN
14
ISOGND
1531 BD
ZCPOS ZCNEG
5
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