HT7A3942 Datasheet, PDF (6/11 Pages) Holtek Semiconductor Inc – High Performance Current Mode PWM Controller

The Green Mode Oscillator types supplied by other
PWM Controller providers are plagued by the
problems of Acoustic-Noise. This is because, under
the conditions of light loads, the frequency will keep
decreasing through Human Acoustic Range (from
20Hz to 20kHz), these audio frequencies may create
audible noise in the transformer. Holtek’s HT7A3942
patented Green Mode Oscillator designed using an
advanced Non-Acoustic Noise Scheme to prevent
the generation of frequencies in the audio frequency
band, thus eliminating any transformer noise.
HT7A3942
Figure 10. UVLO Scheme and Start-Up Current
Current Sense and Leading-Edge
Blanking (LEB)
A Leading-Edge Blanking Scheme is integrated in
the device to prevent false triggering due to feedback
current spikes which may appear on the CS pin,
further eliminate the need for R-C filter which is
always a requirement in the traditional current mode
PWM Controller applications.
Figure 9. Oscillator Behavior Compared with
HT7A3942 and other Green Mode PWM Controller
Under Voltage Lockout (UVLO)
An UVLO comparator is implemented in to ensure
that the device is fully functional before the output
stage is enabled. As shown in Fig. 10, a hysteresis
is provided to prevent the PWM Controller from
shutting down during any voltage dips which might
occur during startup process. The turn-on and turn-
off threshold levels are set at 16.0V and 10.0V,
respectively.
Figure 11. LEB with R-C Filter Removed
Rev. 1.00
6
May 27, 2011