Datasheet

LT3465/LT3465A
11
3465afa
CTRL PWM DUTY CYCLE (%)
0
AVERAGE FEEDBACK VOLTAGE (mV)
200
180
160
140
120
100
80
60
40
20
0
80
3465A F07f
20
40
60
100
4 LEDs
3 LEDs
2 LEDs
30kHz PWM
C
OUT
= 0.22µF
CTRL PWM DUTY CYCLE (%)
0
AVERAGE FEEDBACK VOLTAGE (mV)
200
180
160
140
120
100
80
60
40
20
0
80
3465A F07d
2010 30 50 70 90
40
60
100
30kHz
10kHz
1kHz
100Hz
10Hz
C
OUT
= 0.47µF
4 LEDs
CTRL PWM DUTY CYCLE (%)
0
AVERAGE FEEDBACK VOLTAGE (mV)
200
180
160
140
120
100
80
60
40
20
0
80
3465A F07c
20
40
60
100
30kHz
10kHz
1kHz
100Hz
10Hz
C
OUT
= 0.22µF
4 LEDs
CTRL PWM DUTY CYCLE (%)
0
AVERAGE FEEDBACK VOLTAGE (mV)
200
180
160
140
120
100
80
60
40
20
0
80
3465A F07e
20
40
60
100
4 LEDs
3 LEDs
2 LEDs
10kHz PWM
C
OUT
= 0.22µF
Figure 7e.V
FB
vs CTRL PWM Duty Cycle
Figure 7f.V
FB
vs CTRL PWM Duty Cycle
APPLICATIO S I FOR ATIO
WUUU
Figure 7c. V
FB
vs CTRL PWM Duty Cycle Figure 7d. V
FB
vs CTRL PWM Duty Cycle
case. The Average FB Voltage vs PWM Duty Cycle curves
of different PWM frequencies with different output ca-
pacitors are shown in Figures 7c and 7d respectively. For
PWM frequency lower than 1kHz, the curves are almost
linear. For PWM frequency higher than 10kHz, the curves
show strong nonlinearity. Since the cause of the
nonlinearity is the output capacitor charging/discharg-
ing, the output capacitance and output voltage also affect
the nonlinearity in the high PWM frequencies. Because
smaller capacitance corresponds to shorter capacitor
charging/discharging time, the smaller output capaci-
tance has better linearity as shown in Figures 7c and 7d.
Figures 7e and 7f show the output voltage’s effect to the
curves. The PWM signal should be at least 1.8V in
magnitude; lower voltage will lower the feedback voltage
as shown in Equation 1.