ncp4303a ON Semiconductor, ncp4303a Datasheet - Page 21

• Manufacturer Part Number: ncp4303a
• Description: Ncp4303a/b Secondary Side Synchronous Rectification Driver For High Efficiency Smps Topologies
• Manufacturer: ON Semiconductor

calculated as:
capacitor (Ct) charging, one can calculate the minimum
on−time duration using this equation.
OFF times are independent of the V
to 300 ns and minimum T
prevent any potential issues with the minimum T
T
off
T
Current through the Min_Ton adjust resistor can be
As the same current is used for the internal timing
As can be seen from Equation 5, the minimum ON and
The absolute minimum T
on_min
6
5
4
3
2
1
0
input being shorted to GND.
0
+ C
+ C
Figure 48. Min T
Figure 47. Internal Connection of the Min_Ton Generator (the Min_Toff Works in the Same Way)
10
t
t
@ R
@
I
R_Ton_min
Ton_min
I
R_Ton_min
V
ref
20
R
off
min_Ton
on
+ C
on
+
duration to 600 ns in order to
duration is internally clamped
Adjust Characteristic
30
R
t
+
Ton_min
(kW)
V
ref
R
ref
Ton_min
V
V
ref
ref
40
or V
CC
50
level. The
on
http://onsemi.com
(eq. 4)
(eq. 5)
and/or
60
21
internal capacitor size would be too high if we would use
directly I
the internal current mirror ratio. One can then calculate the
minimum T
equations:
accuracy of Equations 6 and 7 when T
selected near to their minimum possible values. Please refer
to Figure 48 and 49 for measured minimum on and off time
charts.
off time blanking periods. With NCP4303 it is possible to
modulate blanking periods by using an external NPN
transistor – refer to Figure 50. The modulation signal can be
T
T
6
5
4
3
2
1
0
Note that the internal timing comparator delay affects the
Some applications may require adaptive minimum on and
on_min
off_min
0
Figure 49. Min T
R_Ton_min
+ 9.82 * 10
+ 9.56 * 10
10
on
and T
current thus this current is decreased by
20
−11
−11
off
R
* R
* R
min_Toff
off
blanking periods using below
T_on_min
T_off_min
Adjust Characteristic
30
(kW)
) 4.66 * 10
) 5.397 * 10
40
on
/T
off
50
−8
−8
times are
[ms]
[ms]
(eq. 6)
(eq. 7)
60