NCP1251

www.onsemi.com

6

ELECTRICAL CHARACTERISTICS

Symbol

Unit

Max

Typ

Min

Pin

Rating

INTERNAL OSCILLATOR

Oscillation frequency (65 kHz version)

−

61

65

71

kHz

Oscillation frequency (100 kHz version)

−

92

100

108

kHz

Maximum duty−cycle

−

76

80

84

%

−

±5

%

Swing frequency

−

240

Hz

FEEDBACK SECTION

Internal pull−up resistor

2

20

k

W

Equivalent ac resistor from FB to GND

2

16

k

W

Pin 2 to current setpoint division ratio

−

4.2

Feedback voltage below which the peak current is frozen

2

1.05

V

FREQUENCY FOLDBACK

Frequency foldback level on the feedback pin –

[45% of maximum peak current

−

1.5

V

Frequency foldback level on the feedback pin –

[59% of maximum peak current

(F version only)

−

1.9

V

Transition frequency below which skip−cycle occurs

−

22

26

30

kHz

350

mV

(F version only)

1.5

V

Skip−cycle level voltage on the feedback pin

−

300

mV

Skip

hysteresis

Hysteresis on the skip comparator – (Note 5)

−

30

mV

INTERNAL SLOPE COMPENSATION

Internal ramp level @ 25

°C – (Note 7)

4

2.5

V

Internal ramp resistance to CS pin

4

20

k

W

PROTECTIONS

Latching level input

3

2.7

3

3.3

V

Blanking time after drive turn off

1

1.0

ms

Number of clock cycles before latch confirmation

−

4.0

OVP detection time constant

1

600

ns

Timer

Internal auto−recovery fault timer duration

−

100

130

160

ms

5

24

25.5

27

V

5

20

ms

Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product

performance may not be indicated by the Electrical Characteristics if operated under different conditions.

4. For design robustness, we recommend to inject 60

mA as a minimum at the lowest input line voltage.

5. Guaranteed by design

6. See characterization table for linearity over negative bias voltage

7. A 1 M

W resistor is connected from pin 3 to the ground for the measurement.