Datasheet
Primary
Powerand
Switches
Power
Transformer
ToSupply
Monitor
ToPWM
Controller
RFCoupling
Transformer
STATUS
DRIVERB
DRIVERA
UC2901
EXTCLK
CT
Oscillator
X4
10%
-/+
+/-
E/A
1.5V
Reference
RT
V
IN
-
+
V
IN
COMP
INV
NI
VREF
GND
Supply
Output
UC2901-EP
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SLUS709A –DECEMBER 2006–REVISED MARCH 2010
APPLICATION INFORMATION
The error amplifier compensation terminal, pin 12, is intended as a source of feedback to the amplifier's inverting
input at pin 11. For most applications, a series DC blocking capacitor should be part of the feedback network.
The amplifier is compensated internally for unity feedback.
The waveform at the driver outputs is a squarewave, with an amplitude that is proportional to the error amplifier
input signal. There is a fixed 12 dB of gain from the error amplifier compensation pin to the modulator driver
outputs. The frequency of the output waveform is controlled by either the internal oscillator or an external clock
signal.
With the internal oscillator, the squarewave has a fixed 50% duty cycle. If the internal oscillator is disabled by
connecting pin 1, C
R
, to V
IN
, then the frequency and duty cycle of the output is determined by the input clock
waveform at pin 2. If the oscillator remains disabled, and there is not clock input at pin 2, there will be a linear
12-dB signal gain to one or the other of the driver outputs, depending on the DC state of pin 2.
The driver outputs are emitter followers that source a minimum of 15 mA of current. The sink current, internally
limited at 700 mA, can be increased by adding resistors to ground at the driver outputs.
Figure 4. Transformer-Coupled Feedback
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