Datasheet

R
T
+
3 V
(
10 mA
)
ǒ
1 * D
MAX
Ǔ
C
T
+
ǒ
1.6 D
MAX
Ǔ
ǒ
R
T
f
Ǔ
(1)
UDG−95102
R C
C
T
R
T
IR
3 V
IC−IR
CLK
ID = 10 mA
LEB
V
TH
1 k 10 k
70
75
80
85
90
95
100
100 k
D
MAX
− Maximum Duty Cycle − %
R
T
− Timing Resistance − W
MAXIMUM DUTY CYCLE
vs
TIMING RESISTANCE
10 M
1 M
100 k
10 k
1 k
10 k
100 k
R
T
− Timing Resistance − W
OSCILLATOR FREQUENCY
vs
TIMING RESISTANCE
f − Frequency − Hz
UC2825A-EP
www.ti.com SGLS305D –JULY 2005–REVISED SEPTEMBER 2010
APPLICATION INFORMATION
The oscillator of the UC2825A-EP is a sawtooth. The rising edge is governed by a current controlled by the RT
pin and value of capacitance at the CT pin (C
CT
). The falling edge of the sawtooth sets dead time for the outputs.
Selection of RT should be done first, based on desired maximum duty cycle. CT then can be chosen, based on
the desired frequency (RT) and D
MAX
. The design equations are:
Recommended values for R
T
range from 1 kΩ to 100 kΩ. Control of D
MAX
less than 70% is not recommended.
Figure 1. Oscillator
Figure 2. Figure 3.
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Product Folder Link(s): UC2825A-EP