ON Semiconductor NCP1219PRINTGEVB, Руководство пользователя

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NCP1219PRINTGEVB
http://onsemi.com
11
Figure 19 compares the measured results to the frequency
response produced by the “FLYBACK AUTO” tool. There
is good agreement for frequencies at or below the crossover
frequency. There is divergence at higher frequencies due to
the double pole of the output filter on the evaluation board.
The frequency of the double pole (f
dp
) is given by
Equation 33.
f
dp
+
1
2 @ p @ L1 @ C16
Ǹ
(eq. 33)
where L1 is the output inductor and C16 is the output filter
capacitor, which results in a pole frequency of 7.2 kHz. The
“FLYBACK AUTO” tool does not include an output filter
in the compensation design.
Figure 19. Total Loop Response Measured at Low Line and Nominal Load Current
Mag (dB)
SimMag (dB)
Phase (deg)
Sim Phase (deg)
10 100 1000 10000 100000
FREQUENCY (Hz)
60
50
40
30
20
10
0
− 10
− 20
− 30
70
200
160
120
80
40
0
− 40
− 80
− 120
− 160
− 200
PHASE (
°
)
Mag (dB)
PM = 60 °
f
C
= 1.3 kHz
Skip Mode for Reduced Standby Power Dissipation
The NCP1219 employs an adjustable skip level that
reduces input power in light load and standby conditions.
V
FB
is compared to V
Skip/latch
. If V
FB
decreases to less than
V
Skip/latch
, the drive pulses stop until the feedback loop
causes V
FB
to increase to greater than V
Skip/latch
. V
Skip/latch
is adjustable by connecting an external resistor between the
Skip/latch and GND pins, as shown in Figure 20. If no
resistor is connected between the pins, the skip threshold is
the default value, V
skip
. If the voltage on the Skip/latch pin
exceeds 1.3 V, then the skip threshold is clamped to
V
skip(MAX)
, typically 1.3 V.
Skip/latch
S
R Q
-
+
FB
latch-off, reset
when VCC < VCC(reset)
R
skip
V
latch
-
Skip
Comparator
+
2 V
50 us
filter
V
Skip/Latch
V
Skip(MAX)
V
Skip
51.3 k
Rupper
42.0 k
Rlower
-
+
C
skip
V
Skip/latch
To DRV
latch
reset
Figure 20. Adjustable Skip Level Circuit Configuration