Datasheet

LT1249
5
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
TEMPERATURE (°C)
SYNCHRONIZATION THRESHOLD (V)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1249 G11
75
–25 25 125–50 0 50
100
Synchronization Threshold
at CA
OUT
Voltage Amp Sink Current Limits
(Threshold)
M
OUT
VOLTAGE (V)
–2.4
–1.2
0
M
OUT
CURRENT (mA)
1.2
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
1249 G12
1.2
2.4
125°C
25°C
–50°C
M
OUT
Pin Characteristics
TEMPERATURE (°C)
I
M(MAX)
× R
MOUT
(V)
1249 G15
–1.30
–1.25
–1.20
–1.15
–1.10
–1.05
–1.00
–0.95
–0.90
–75 –25–50 250 50 100
75
125
Maximum Multiplier Output
Voltage (I
M(MAX)
× R
MOUT
)
Transconductance of Current
Amplifier Over Temperature
TEMPERATURE (°C)
–50
TRANSCONDUCTANCE (µmho)
100
1249 G13
050
400
350
300
250
200
150
100
50
0
–25 25 75 125
Maximum Duty Cycle
TEMPERATURE (°C)
DUTY CYCLE (%)
100
99
98
97
96
95
94
93
92
91
90
1249 G16
75
–25 25 125–50 0 50
100
TEMPERATURE (°C)
–75
CURRENT (µA)
–25–50 250 50 100
75
125
1249 G14
60
50
40
30
20
10
0
UP THRESHOLD
DOWN THRESHOLD
NOTE: THESE SINK CURRENT THRESHOLDS ARE
FOR OVERVOLTAGE PROTECTION FUNCTION.
GND (Pin 1): Ground.
CA
OUT
(Pin 2): This is the output of the current amplifier
that senses and forces the line current to follow the
reference signal that comes from the multiplier by com-
manding the pulse width modulator. When CA
OUT
is low,
the modulator has zero duty cycle.
M
OUT
(Pin 3): The multiplier current goes out of this pin
through the 4k resistor R
MOUT
. The voltage developed
across R
MOUT
is the reference voltage of the current loop
and it is limited to 1.1V. The noninverting input of the
current amplifier is also tied to R
MOUT
. In operation, M
OUT
is normally at negative potential and only AC signals
appear at the noninverting input of the current amplifier.
I
AC
(Pin 4): This is the AC line voltage sensing input to the
multiplier. It is a current input that is biased at 2V to
minimize the crossover dead zone caused by low line
voltage. A 25k resistor is in series with the current input,
so that a small external capacitor can be used to filter out
the switching noise from the high impedance lines.
VA
OUT
(Pin 5): This is the output of the voltage error
amplifier. The output is clamped at 12V. When the output
goes below 1.5V, the multiplier output current is zero.
PIN FUNCTIONS
UUU