8
Power Supply 3.3V Regulator
3.3V
The USB controller, U6000, the I/O circuitry of the DSP, U7000, and the digital processing portions of the
CODEC, U4000 all require power from +3.3V. This circuitry is biased both during normal operation and stand-by,
so no enable control is required.
U902 is a TI TL5001 switch-mode PWM regulator control circuit. The output is open-collector, and drives the
base of the PNP power transistor, Q9031. Q9032, D9200, R9240, and C9220
provide a boot-strapped circuit to speed the turn-off of Q9031. R9236 and R9237 form a potential divider to
establish the DC operating point of the regulator at +3.3 volts. C9202 provides a lead compensation in the
feedback circuit. R9238 limits the frequency range of the lead compensation.
C9211 is applied around the error amplifier of the TL5001 to create a lag compensation. R9235 limits the fre-
quency range of the lag compensation.
R9232 establishes the approximately
50
kHz switching frequency for the PWM generator. C9209 generates a
soft-start ramp when TL5001 starts switching.
