L6520, L6521

Functions description

Doc ID 16998 Rev 3

9/19

5

Functions description

5.1

Start-up

of FPRE pin to detect the programmed preheating frequency and the selected ignition mode

(instant or preheated start). When all the IC internal functions are ready, the driver-outputs

are released.

If the preheated start is selected, the half-bridge oscillates at the programmed preheating

frequency, otherwise it starts from 85 kHz (typ.).

5.2

Preheating and instant start

The preheating time is 1.5 s (typ.) in the L6520 and 0.8 s (typ.) in the L6521. The FPRE pin

embeds a precise current reference: the voltage read by this pin sets the preheating

frequency or enables the instant start. If the FPRE pin is connected to ground, the instant

start is active and the IC runs immediately into ignition sequence from the starting frequency

of 85 kHz. If the pin FPRE is connected to a resistor equal or higher than 196

Ω, the

preheating frequency can be programmed from 55 kHz upwards till 100 kHz (1.5 kHz/step)

accordingly to

Table 6. For the best precision the resistor tolerance should be less or equal

to 1%. After the preheating sequence, the IC runs into ignition mode.

Table 6.

Preheating and instant start

Instant start

0

77.5

5490

55

196

79

6190

56.5

383

80.5

6980

58

576

82

7870

59.5

806

83.5

8660

61

1050

85

9530

62.5

1300

86.5

10500

64.

1580

88

11500

65.5

1870

89.5

12700

67

2210

91

14000

68.5

2550

92.5

15400

70

2940

94

16900

71.5

3400

95.5

18700

73

3830

97

20500

74.5

4320

98.5

22600

76

4870

100

24900