AIC3843 Datasheet, PDF (6/11 Pages) Analog Intergrations Corporation – Current-Mode PWM Controller

AIC3843
Oscillator Section
8
V_REF
R_T
4
R_T/C_T
5
C_T
GND
1.72
For RT>5k, f≈ RT * CT
Fig. 4-1
30
10
3
0
1
0.31
10
100
CT (nF)
Deadtime vs CT (RT>5KΩ)
Fig. 4-2
100
CT=100nF
30
47nF
22nF
10
10nF
4.7nF
2.2nF
1.0nF
3
10²
3
10
10⁴
10⁵
10⁶
Frequency (Hz)
Timing Resistance vs. Frequency
Fig. 4-3
7
6
Vcc=15V
5
TA=+25° solid line
TA=-55° dash line
3
2
SOURCE SAT
(Vcc-VoH)
1
SINK SAT (Vol)
0
0.01
0.1
1
Output Current, Source or Sink - (A)
Fig. 4-4 Output saturation characteristics
80
0
60
-50
40
-100
20
-150
0
-200
-20
10
100
1k
10k
100k
1M
Frequency (Hz)
Fig. 4-5 Error Am plifier Open-Loop Frequency Response
Open-Loop Laboratory Fixture
VREF
4.7K
1K
ERROR
AMP
ADJUST
4.7K
2N2222
100K
5K
I_SENSE
ADJUST
R1
1
COMP
AIC3843
8
VREF
2
V _FB
7
VCC
3
I_SENSE
6
OUTPUT
4 _RT/CT
5
GND
A
0 . 1µ F
1k
0 . 1µ F
1W
VCC
OUTPUT
GND
C_T
High peak currents associated with capacitive loads necessitate careful grounding techniques.
Timing and bypass capacitors should be connected close to pin 5 in a single point ground. The
transistor and 5k potentiometer are used to sample the oscillator waveform and apply an adjustable
ramp to pin 3.
Fig. 5
6