Datasheet
Table Of Contents
- Figure 1. Typical topology
- Table 1. Device summary
- 1 Block diagram
- 2 Typical power
- 3 Pin settings
- 4 Electrical data
- 5 Typical electrical characteristics
- Figure 7. Current limit vs. TJ
- Figure 8. Switching frequency vs. TJ
- Figure 9. Drain start voltage vs. TJ
- Figure 10. HFB vs. TJ
- Figure 11. Brownout threshold vs. TJ
- Figure 12. Brownout hysteresis vs. TJ
- Figure 13. Brownout hysteresis current vs. TJ
- Figure 14. Operating supply current (not switching) vs. TJ
- Figure 15. Operating supply current (switching) vs. TJ
- Figure 16. Current limit vs. RLIM
- Figure 17. Power MOSFET ON resistance vs. TJ
- Figure 18. Power MOSFET breakdown voltage vs. TJ
- Figure 19. Thermal shutdown
- 6 Typical circuit
- 7 Efficiency performances for a typical flyback converter
- 8 Operation description
- 8.1 Power section and gate driver
- 8.2 High voltage startup generator
- 8.3 Power-up and soft-start
- 8.4 Power down operation
- 8.5 Auto-restart operation
- 8.6 Oscillator
- 8.7 Current mode conversion with adjustable current limit set point
- 8.8 Overvoltage protection (OVP)
- 8.9 About the CONT pin
- 8.10 Feedback and overload protection (OLP)
- 8.11 Burst mode operation at no load or very light load
- 8.12 Brownout protection
- 8.13 2nd level overcurrent protection and hiccup mode
- 9 Package mechanical data
- 10 Revision history
VIPER37 Operation description
Doc ID 022218 Rev 1 23/35
Figure 27. Timing diagram: behavior after short-circuit
8.6 Oscillator
The switching frequency is internally fixed to 60 kHz or 115 kHz. In both cases the switching
frequency is modulated by approximately ±4 kHz (60 kHz version) or ±8 kHz
(115 kHz version) at a 250 Hz (typ.) rate, so that the resulting spread-spectrum action
distributes the energy of each harmonic of the switching frequency over a number of side-
band harmonics having the same energy on the whole but smaller amplitudes.
8.7 Current mode conversion with adjustable current limit set
point
This device is a current mode converter: the drain current is sensed and converted into
voltage that is applied to the non-inverting pin of the PWM comparator. This voltage is
compared with the one on the feedback pin through a voltage divider on a cycle-by-cycle
basis.
The device has a default current limit value, I
Dlim
, that the user can adjust according to the
electrical specifications, through the R
LIM
resistor connected to the CONT pin (see
Figure 16
).
The CONT pin has a minimum current sunk, needed to activate the I
Dlim
adjustment: without
R
LIM
or with high R
LIM
(i.e. 100 kΩ), the current limit is fixed to the default value (see I
Dlim
,
Tabl e 8
).
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