Datasheet

ADJ: The ADJ pin is used to provide a 12V or an 18V
regulated supply without additional external components.
To select the 12V option, ADJ pin is left open. To select
the 18V option, ADJ pin must be grounded. For other out-
put voltages less than 18V, a resistor divider between
V
OUT, ADJ and GND is needed. Note, however, that for
output voltages less than V
CC, the device needs addi-
tional bootstrapping to V
CC from an external source such
as the line voltage. If so, precautions must be taken to
ensure that total I
CC does not exceed 5mA.
C
T (timing capacitor): The signal voltage across CT has
a peak-to-peak swing of 3.7V for 9V V
CC. As the voltage
on C
T crosses the oscillator upper threshold, DRIVE goes
low. As the voltage on C
T crosses the oscillator lower
threshold, DRIVE goes high.
DRIVE: This output is a CMOS stage capable of sinking
200mA peak and sourcing 150mA peak. The output volt-
age swing is 0 to V
CC.
GND (chip ground): All voltages are measured with re-
spect to GND.
T
OFF (regulated output control): TOFF sets the dis-
charge current of the timing capacitor through an external
resistor connected between V
OUT and TOFF.
T
ON (line voltage control): TON serves three functions.
When C
T is discharging (off time), the current through
T
ON is routed to VCC. When CT is charging (on time), the
current through T
ON is split 80% to set the CT charge
time and 20% to sense minimum line voltage which oc-
curs for a T
ON current of 220µA. For a minimum line volt-
age of 80V, R
ON is 330kΩ.
The C
T voltage slightly affects the value of the charge
current during the on time. During this time, the voltage at
the T
ON pin increases from approximately 2.5V to 6.5V.
V
CC (chip supply voltage): The supply voltage of the
device at pin V
CC is internally clamped at 9V. Normally,
V
CC is not directly powered from an external voltage
source such as the line voltage. In the event that V
CC is
directly connected to a voltage source for additional boot-
strapping, precautions must be taken to ensure that total
I
CC does not exceed 5mA.
V
OUT (regulated output): The VOUT pin is directly con-
nected to the power supply output voltage. When V
OUT is
greater than V
CC, VOUT bootstraps VCC.
UCC1889
UCC2889
UCC3889
PIN DESCRIPTIONS
BLOCK DIAGRAM
UDG-93064-2
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