LT1249 Datasheet, PDF (5/12 Pages) Linear Technology – Power Factor Controller

TYPICAL PERFORMANCE CHARACTERISTICS
LT1249
Synchronization Threshold
at CA_OUT
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–50 –25
0 25 50 75 ₁₀₀ 125
TEMPERATURE (°C)
1249 G11
Voltage Amp Sink Current Limits
(Threshold)
60
50
UP THRESHOLD
40
30
DOWN THRESHOLD
20
10
0
–75 –50 –25 0 25 50 75 100 125
TEMPERATURE (°C)
NOTE: THESE SINK CURRENT THRESHOLDS ARE
FOR OVERVOLTAGE PROTECTION FUNCTION. 1249 G14
M_OUT Pin Characteristics
1.2
1.0
125°C
25°C
0.8
–50°C
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–2.4
–1.2
0
1.2
M_OUT VOLTAGE (V)
2.4
1249 G12
Maximum Multiplier Output
Voltage (I_M(MAX) • R_MOUT)
–1.30
–1.25
–1.20
–1.15
–1.10
–1.05
–1.00
–0.95
–0.90
–75 –50 –25 0 25 50 75 100 125
TEMPERATURE (°C)
1249 G15
Transconductance of Current
Amplifier Over Temperature
400
350
300
250
200
150
100
50
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1249 G13
Maximum Duty Cycle
100
99
98
97
96
95
94
93
92
91
90
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 ¹²⁵
1249 G16
PIN FUNCTIONS
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 32k 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.
5