November 1998
PRELIMINARY
ML4805
Variable Feedforward PFC/PWM Controller Combo
GENERAL DESCRIPTION
The ML4805 is a controller for power factor corrected, switched mode power supplies. Similar to the ML4801, the ML4805 may be used for voltage mode operation. Key features of this combined PFC and PWM controller are low start-up and operating currents. Power Factor Correction (PFC) allows the use of smaller, lower cost bulk capacitors, reduces power line loading and stress on the switching FETs, and results in a power supply that fully complies with IEC1000-2-3 specifications. The ML4805 includes circuits for the implementation of a leading edge, average current “boost” type power factor correction and a trailing edge pulse width modulator.
The PFC frequency of the ML4805 is automatically set at half that of the PWM frequency generated by the internal oscillator. This technique allows the user to design with smaller output components while maintaining the optimum operating frequency for the PFC. An overvoltage comparator shuts down the PFC section in the event of a sudden decrease in load. The PFC section also includes peak current limiting and input voltage brownout protection.
FEATURES
■Internally synchronized PFC and PWM in one IC
■Low start-up current (200 A typ.)
■Low operating current (5.5mA typ.)
■Low total harmonic distortion
■Reduces ripple current in the storage capacitor between the PFC and PWM sections
■Average current continuous boost leading edge PFC
■High efficiency trailing edge PWM optimized for voltage mode operation
■Current fed gain modulator for improved noise immunity
■Brown-out control, overvoltage protection, UVLO, and soft start
BLOCK DIAGRAM |
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18 |
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1 |
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15 |
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VEAO |
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IEAO |
POWER FACTOR CORRECTOR |
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VCC |
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VCC |
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OVP |
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VFB |
VEA |
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VREF |
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17 |
- |
1.6kΩ |
IEA |
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7.5V |
16 |
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REFERENCE |
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2.75V |
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2.5V |
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– |
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IAC |
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Q |
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2 |
GAIN |
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-1V |
+ |
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VRMS |
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R |
Q |
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MODULATOR |
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4 |
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PFC OUT |
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1.6kΩ |
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PFC ILIMIT |
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ISENSE |
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14 |
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3 |
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RAMP 1 |
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R |
Q |
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8 |
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RTCT |
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OSCILLATOR |
÷2 |
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7 |
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PGND |
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RAMP 2 |
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DUTY CYCLE |
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12 |
9 |
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LIMIT |
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8V |
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VDC |
1.25V |
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- |
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6 |
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+ |
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PWM OUT |
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VCC |
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- |
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VIN OK |
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Q |
13 |
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VFB |
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SS |
25µA |
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R |
Q |
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5 |
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2.5V |
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1.5V |
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ILIM |
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8V |
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AGND |
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DC ILIMIT |
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10 |
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11 |
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PULSE WIDTH MODULATOR |
VCC |
UVLO |
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REV. 1.1 3/9/2001
ML4805
PIN CONFIGURATION
ML4805
18-Pin PDIP (P18)
18-Pin SOIC (S18)
IEAO |
1 |
18 |
VEAO |
IAC |
2 |
17 |
VFB |
ISENSE |
3 |
16 |
VREF |
VRMS |
4 |
15 |
VCC |
SS |
5 |
14 |
PFC OUT |
VDC |
6 |
13 |
PWM OUT |
RTCT |
7 |
12 |
PGND |
RAMP 1 |
8 |
11 |
AGND |
RAMP 2 |
9 |
10 |
ILIM |
TOP VIEW
PIN DESCRIPTION
PIN |
NAME |
FUNCTION |
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PIN |
NAME |
FUNCTION |
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1 |
IEAO |
PFC transconductance current error |
9 |
RAMP 2 |
PWM ramp sense input |
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amplifier output |
10 |
ILIM |
PWM current limit sense input |
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2 |
IAC |
PFC gain control reference input |
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11 |
AGND |
Analog ground |
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3 |
ISENSE |
Current sense input to the PFC current |
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12 |
PGND |
Power ground |
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limit comparator |
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4 |
VRMS |
Input for PFC RMS line voltage |
13 |
PWM OUT |
PWM driver output |
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compensation |
14 |
PFC OUT |
PFC driver output |
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5 |
SS |
Connection point for the PWM soft start |
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capacitor |
15 |
VCC |
Positive supply (connected to an |
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6 |
VDC |
PWM voltage feedback input |
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internal shunt regulator). |
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16 |
VREF |
Buffered output for the internal 7.5V |
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7 |
RTCT |
Connection for oscillator frequency |
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reference |
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setting components |
17 |
VFB |
PFC transconductance voltage error |
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8 |
RAMP 1 |
PFC ramp input |
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amplifier input |
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18 |
VEAO |
PFC transconductance voltage error |
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amplifier output |
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2 |
REV. 1.1 3/9/2001 |
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ML4805 |
ABSOLUTE MAXIMUM RATINGS |
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Absolute maximum ratings are those values beyond which |
Junction Temperature ............................................. |
150°C |
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the device could be permanently damaged. Absolute |
Storage Temperature Range ...................... |
–65°C to 150°C |
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maximum ratings are stress ratings only and functional |
Lead Temperature (Soldering, 10 sec) ..................... |
260°C |
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device operation is not implied. |
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Thermal Resistance (θJA) |
70°C/W |
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Plastic DIP ........................................................ |
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VCC .............................................................................................. |
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18V |
Plastic SOIC ................................................... |
100°C/W |
ISENSE Voltage .................................................. |
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-3V to 5V |
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Voltage on Any Other Pin ...... |
GND - 0.3V to VCC + 0.3V |
OPERATING CONDITIONS |
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IREF ........................................................................................... |
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20mA |
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IAC Input Current ..................................................... |
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10mA |
Temperature Range |
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Peak PFC OUT Current, Source or Sink ................. |
500mA |
0°C to 70°C |
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Peak PWM OUT Current, Source or Sink............... |
500mA |
ML4805CX ................................................. |
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PFC OUT, PWM OUT Energy Per Cycle ................... |
1.5µJ |
ML4805IX ............................................... |
-40°C to 85°C |
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ELECTRICAL CHARACTERISTICS
Unless otherwise specified, VCC = 15V, RT = 29.4kΩ, RRAMP1 = 15.4kΩ, CT = 270pF, CRAMP1 = 620pF, TA = Operating Temperature Range (Note 1)
SYMBOL |
PARAMETER |
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CONDITIONS |
MIN |
TYP |
MAX |
UNITS |
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VOLTAGE ERROR AMPLIFIER |
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Input Voltage Range |
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0 |
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5 |
V |
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Transconductance |
V |
= V , VEAO = 3.75V |
40 |
65 |
80 |
µ |
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NON INV |
INV |
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Ω |
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Feedback Reference Voltage |
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2.43 |
2.50 |
2.57 |
V |
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Input Bias Current |
Note 2 |
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-0.5 |
-1.0 |
µA |
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Output High Voltage |
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6.0 |
6.7 |
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V |
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Output Low Voltage |
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0.1 |
0.4 |
V |
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Source Current |
∆VIN = ±0.5V, VOUT = 6V |
-40 |
-70 |
-150 |
µA |
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Sink Current |
∆VIN = ±0.5V, VOUT = 1.5V |
40 |
70 |
150 |
µA |
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Open Loop Gain |
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60 |
70 |
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dB |
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PSRR |
11V < VCC < 16.5V |
60 |
70 |
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dB |
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CURRENT ERROR AMPLIFIER |
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Input Voltage Range |
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-1.5 |
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2 |
V |
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Transconductance |
V |
= V , VEAO = 3.75V |
60 |
100 |
120 |
µ |
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NON INV |
INV |
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Ω |
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Input Offset Voltage |
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0 |
8 |
15 |
mV |
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Input Bias Current |
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-0.5 |
-1.0 |
µA |
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Output High Voltage |
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6.0 |
6.7 |
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V |
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Output Low Voltage |
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0.65 |
1.0 |
V |
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Source Current |
∆VIN = ±0.5V, VOUT = 6V |
-40 |
-70 |
-150 |
µA |
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Sink Current |
∆VIN = ±0.5V, VOUT = 1.5V |
40 |
70 |
150 |
µA |
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Open Loop Gain |
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55 |
65 |
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dB |
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PSRR |
11V < VCC < 16.5V |
60 |
75 |
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dB |
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REV. 1.1 3/9/2001 |
3 |
ML4805
ELECTRICAL CHARACTERISTICS (Continued)
SYMBOL |
PARAMETER |
CONDITIONS |
MIN |
TYP |
MAX |
UNITS |
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OVP COMPARATOR |
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Threshold Voltage |
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2.65 |
2.75 |
2.85 |
V |
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Hysteresis |
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175 |
250 |
325 |
mV |
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PFC ILIMIT COMPARATOR |
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Threshold Voltage |
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-0.9 |
-1.0 |
-1.1 |
V |
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∆PFC ILIMIT Threshold - Gain Modulator Output |
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120 |
220 |
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mV |
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Delay to Output |
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150 |
300 |
ns |
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DC ILIMIT COMPARATOR |
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Threshold Voltage |
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1.4 |
1.5 |
1.6 |
V |
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Input Bias Current |
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±0.3 |
±1 |
A |
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Delay to Output |
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150 |
300 |
ns |
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VIN OK COMPARATOR |
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Threshold Voltage |
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2.4 |
2.5 |
2.6 |
V |
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Hysteresis |
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0.8 |
1.0 |
1.2 |
V |
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GAIN MODULATOR |
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Gain (Note 3) |
IAC = 100 A, VRMS = VFB = 0V |
0.65 |
0.85 |
1.05 |
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IAC = 50 A, VRMS = 1V, VFB = 0V |
1.90 |
2.20 |
2.40 |
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IAC = 50 A, VRMS = 1.8V, VFB = 0V |
0.90 |
1.05 |
1.25 |
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IAC = 100 A, VRMS = 3.3V, VFB = 0V |
0.20 |
0.30 |
0.40 |
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Bandwidth |
IAC = 100 A |
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10 |
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MHz |
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Output Voltage |
IAC = 350 A, VRMS = 1V, |
0.65 |
0.75 |
0.85 |
V |
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VFB = 0V |
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OSCILLATOR |
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Initial Accuracy |
TA = 25ºC |
188 |
200 |
212 |
kHz |
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Voltage Stability |
11V < VCC < 16.5V |
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1 |
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% |
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Temperature Stability |
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2 |
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% |
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Total Variation |
Line, Temp |
182 |
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218 |
kHz |
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Ramp Valley to Peak Voltage |
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2.5 |
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V |
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PFC Dead Time |
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350 |
470 |
600 |
ns |
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CT Discharge Current |
VRAMP 2 = 0V, VRAMP 1 = 2.5V |
3.5 |
5.5 |
7.5 |
mA |
4 |
REV. 1.1 3/9/2001 |
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