ON Semiconductor NCP1060, Руководство пользователя

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NCP1060, NCV1060, NCP1063, NCV1063
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S
R
Q
I
COMP
to CS setpoint
I
Freeze
I
pk(0 )
Vramp + Vsense
OSC
I
LMOP
I
LMDEC
I
LMDEC
I
LMOP
0
25
m
A 250
m
A
I
PKL
I
COMP
MOSFET
LIM/ OPP
D4
C2
VCC
R
OPPU
R
OPPL
Aux
winding
Figure 43. The OPP Circuitry Affects the Maximum Peak Current Set Point
Ramp Compensation and Ipk Set−point
In order to allow the NCP106X to operate in CCM with a
duty cycle above 50%, a fixed slope compensation is
internally applied to the current−mode control.
Here we got a table of the ramp compensation, the initial
current set point, and the final current set−point of different
versions of switcher.
NCP1060 NCP1063
f
sw
60 kHz 100 kHz 60 kHz 100 kHz
S
a
8.4 mA/
m
s 14 mA/
m
s 15.6 mA/
m
s 26 mA/
m
s
I
pk(Duty
=50%)
250 mA 650 mA
I
pk(0)
300 mA 780 mA
Figure 44 depicts the variation of I
PK
set−point vs. the
power switcher duty ratio, which is caused by the internal
ramp compensation.
Figure 44. I
PK
set−point varies with power switch on time, which is caused by the ramp compensation.
0
100
200
300
400
500
600
700
800
900
0% 10% 20% 30% 40% 50% 60% 70%
Ipk set-point [mA]
Dutty Ratio [%]
NCP1060
NCP1063
FB Pin Function
The FB pin is used in non isolated SMPS application only.
Portion of the output voltage is connected into the pin. The
voltage is compared with internal V
REF
(3.3 V) using
Operation Transconductance Amplifier (Figure 45). The
OTAs output is connected to COMP pin. The OTA output is
accessible through the COMP pin and is used for the loop
compensation, usually an RC network. The current
capability of OTA is limited to −150
m
A typically. The
positive current is defined by internal R
COMP(up)
resistor
and V
COMP(ref)
voltage. If FB path loop is broken (i.e. the FB
pin is disconnected), an internal current I
FB
(1
m
A typ.) will
pull up the FB pin and the IC stops switching to avoid
uncontrolled output voltage increasing.
In isolated topology, the FB pin should be connected to
GND pin. In this configuration no current flows from OTA
to COMP pin (OTA is disabled) so the OTA has no influence
on regulation at all.