UCC1580-1,-2,-3,-4
UCC2580-1,-2,-3,-4
UCC3580-1,-2,-3,-4
PIN DESCRIPTIONS (cont.)
SS:
A capacitor from SS to ground programs the soft
start time. During soft start, EAOUT follows the amplitude
of SS’s slowly increasing waveform until regulation is
achieved.
VDD:
Chip power supply pin. VDD should be bypassed
to PGND. The –1 and –3 versions require VDD to ex-
ceed 9V to start and remain above 8.5V to continue run-
ning. A shunt clamp from VDD to GND limits the supply
voltage to 15V. The –2 and –4 versions do not start until
APPLICATION INFORMATION
Note: Waveforms are not to scale.
UDG-95070-2
Figure 1. Output time relationships.
UVLO and Startup
For self biased off-line applications, -2 and -4 versions
(UVLO on and off thresholds of 15V and 8.5V typical)
are recommended. For all other applications, -1 and -3
versions provide the lower on threshold of 9V. The IC re-
quires a low startup current of only 160mA when VDD is
under the UVLO threshold, enabling use of a large trickle
charge resistor (with corresponding low power dissipa-
tion) from the input voltage. VDD has an internal clamp
at 15V which can sink up to 10mA. Measures should be
taken not to exceed this current. For -2 and -4 versions,
5
this clamp must be activated as an indication of reaching
the UVLO on threshold. The internal reference (REF) is
brought up when the UVLO on threshold is crossed. The
startup logic ensures that LINE and REF are above and
SHTDWN is below their respective thresholds before
outputs are asserted. LINE input is useful for monitoring
actual input voltage and shutting off the IC if it falls be-
low a programmed value. A resistive divider should be
used to connect the input voltage to the LINE input. This
feature can protect the power supply from excessive
currents at low line voltages.
TI [ TEXAS INSTRUMENTS ]
