XNE5560CU View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
XNE5560CU Datasheet PDF : 16 Pages
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Philips Semiconductors
Switched-mode power supply control circuit
Product specification
NE/SE5560
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
Typical Frequency Plot vs RT and
f(kHz)
CT
δ
1000
100
90
80
7600
50
40
30
20
10
9
8
7
6
5
4
3
2
1
R=5kΩ
R=10kΩ
R=20kΩ
R=40kΩ
2
2.5
3
3.5
4
4.5 CnF)
100
90
80
70
60
50
40
30
20
10
V16
1
1.5
2
2.5 VZ
Figure 5. Typical Performance Characteristics
SL00364
THEORY OF OPERATION
The following functions are incorporated:
– A temperature-compensated reference source.
– An error amplifier with Pin 3 as input. The output is connected
to Pin 4 so that the gain is adjustable with external resistors.
– A sawtooth generator with a TTL-compatible synchronization
input (Pins 7, 8, 9).
– A pulse-width modulator with a duty cycle range from 0 to 95%.
The PWM has two additional inputs:
Pin 6 can be used for a precise setting of δMAX
Pin 5 gives a direct access to the modulator, allowing for real
constant-current operation:
– A gate at the output of the PWM provides a simple dynamic
current limit.
– A latch that is set by the flyback of the sawtooth and reset by
the output pulse of the above mentioned gate prohibits double
pulsing.
– Another latch functions as a start-stop circuit; it provides a fast
switch-off and a slow start.
– A current protection circuit that operates via the start-stop
circuit. This is a combined function with the current limit circuit,
therefore Pin 11 has two trip-on levels; the lower one for
cycle-by-cycle current limiting, the upper one for current
protection by means of switch-off and slow-start.
– A TTL-compatible remote on/off input at Pin 10, also operating
via the start-stop circuit.
– An inhibit input at Pin 13. The output pulse can be inhibited
immediately.
– An output gate that is commanded by the latches and the inhibit
circuit.
– An output transistor of which both the collector (Pin 15) and the
emitter (Pin 14) are externally available. This allows for normal
or inverse output pulses.
– A power supply that can be either voltage- or current-driven
(Pins 1 and 12). The internally-generated stabilized output
voltage VZ is connected to Pin 2.
– A special function is the so-called feed-forward at Pin 16. The
amplitude of the sawtooth generator is modulated in such a way
that the duty cycle becomes inversely proportional to the
voltage on this pin: δ ~ 1/V16.
– Loop fault protection circuits assure that the duty cycle is
reduced to zero or a low value for open- or short-circuited
feedback loops.
Stabilized Power Supply (Pins 1, 2, 12)
The power supply of the NE5560 is of the well known series
regulation type and provides a stabilized output voltage of typically
8.5V.
This voltage VZ is also present at Pin 2 and can be used for precise
setting of δMAX and to supply external circuitry. Its max. current
capability is 5mA.
The circuit can be fed directly from a DC voltage source between
10.5V and 18V or can be current-driven via a limiting resistor. In the
latter case, internal pinch-off resistors will limit the maximum supply
voltage: typical 23V for 10mA and max. 30V for 30mA.
The low supply voltage protection is active when V(1-12) is below
10.5V and inhibits the output pulse (no hysteresis).
When the supply voltage surpasses the 10.5V level, the IC starts
delivering output pulses via the slow-start function.
1994 Aug 31
7
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