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NCP5604AAGEVB

P1-P3P4-P6P7-P9P10-P12P13-P15
NCP5604A, NCP5604B
http://onsemi.com
10
Figure 9. Using the NCP5604B to Drive a Three LED
Layout
VBAT
1
EN
2
IREF
3
AGND
4
NC
5
LED3
6
LED2
7
LED1
8
PGND
9
C1N
10
C1P
11
VOUT
12
C2P
13
C2N
14
C3P
15
C3N
16
U1
NCP5604B
C2
C3
220 nF/10 V
C4
4.7uF/6.3V
C5
1uF/10V
GND
GND
D3
LWY87S
D2
LWY87S
D1
LWY87S
R1
100k
GND
CONTROL
Vbat
220 nF/10 V
C1
220 nF/10 V
Finally, an external network can be connected across
Vout and ground, but the current through such network will
not be regulated by the NCP5604A chip (see Figure 10).
On top of that, the total current out of the Vout pin shall be
limited to 100 mA.
Figure 10. Extra Load Connected to Vout
NCP5604
12
5
6
7
8
D1
LWY87S
GND
D2
LWY87S
D3
LWY87S
D4
LWY87S
D5
LWY87S
D6
LWY87S
5 mA
5 mA
220R
R1
220R
R2
GND
C5
1 mF/6.3 V
DIMMING
The dimming can be achieved by two means:
• Use a digital PWM signal to control the EN pin
• Use an analog signal to control the reference current
IREF pin.
The digital PWM is straightforward, yielding a zero to
100% duty cycle, but the output current is pulsed since the
system is continuously switched ON/OFF. There is no need
for extra passive component, the clock being provided by
an I/O port from the MCU (see Figure 11).
Figure 11. Basic Digital PWM Dimming Control
VBAT
C2P
C1P
C1N
LED4
LED3
LED2
LED1
1
22
3
6.8 k
R1
GND
4
9
GND
PWM
EN
IREF
AGND
PGND
C2N
C3P
C3N
VOUT
Input PWM Signal Frequency:
100 Hz to 200 kHz
The PWM frequency can be up to 200 kHz once the
circuit has been properly started. On the other hand, with
a 1% to 99% span, the circuit supports a large Duty Cycle
to accommodate any range of dimming. The waveforms
given in Figure 12 illustrate the NCP5604A behavior
during the 50 kHz PWM operation. The same mechanism
applies for the NCP5604B version.
Figure 12. PWM Modulation Span: 1% to 99%
Besides the popular PWM mode, a simple analog
technique can be built with two extra components (one
resistor + one NMOS), the net advantage being a
continuous output current once the operating point has
been stabilized (see Figure 13). The absolute output
current tolerance depends upon the precision of the two
external resistors, the R
DS(on)
of the NMOS being
negligible in front of the resistor value. The example given,
Figure 13 yields a 1.0 mA output current when Q1 is OFF,
NCP5604A, NCP5604B
http://onsemi.com
11
and 23 mA when Q1 is ON. The concept can use either a
DC drive or a pulsed mode to dynamically dim the light out
of the LED.
A different analog approach, but more complex solution,
can be derived from either a DC or a pulsed voltage
associated with a current mirror built with low cost discrete
devices (see Figure 14). The associated filter (R2/R3/C1)
provides a continuous voltage to the current mirror, thus a
digitally controlled continuous output current. Generally
speaking, the PWM frequency could be either in the low
end 20 Hz to 200 Hz band, or above the audio band (25 kHz
and beyond) to make sure the dimming can be adjusted
from zero to 100% without any audible noise. As a matter
of fact, the NCP5604A has been designed to guarantee
200 kHz PWM at the ENABLE pin.
The current mirror can be largely improved by using an
external operational amplifier to get a very stable and
temperature independent current, but such a solution could
turn out to be too expensive and, generally speaking, the
basic structure given, Figure 13, gives good results since
the current depends mostly upon the quality of resistor R2.
Figure 13. Basic Analog Dimming Control
VBAT
C2P
C1P
C1N
LED4
LED3
LED2
LED1
1
22
3
4
9
GND
EN
IREF
AGND
PGND
C2N
C3P
C3N
VOUT
5
6
7
8
ENABLE
150 k
R1
6.8 k
R2
Q1
High Out
Figure 14. Basic Analog PWM Dimming Control
VBAT
C2P
C1P
C1N
LED4
LED3
LED2
LED1
1
22
3
4
9
GND
EN
IREF
AGND
PGND
C2N
C3P
C3N
VOUT
5
6
7
8
ENABLE
GND
Q1B
Q1A
BC846BDW
15 k
R2
GND
10 nF
C1
12 k
R1
PWM
V = 3.3 V
NCP5604A, NCP5604B
http://onsemi.com
12
Figure 15. Startup Operation
SHORT CIRCUIT OPERATION
The circuit is designed to support a short circuit across
Vout and Ground without damage. When a short occurs, the
pulsed output current increases to the maximum peak value
until the output voltage drops below 1 V. At this point, the
pulsed current is limited to 40 mA average (typical), until
the short is removed. The waveforms given in Figure 16
illustrate the functional operation. Similarly, the input
current is limited 300 mA peak (typical) as depicted in
Figure 17.
Figure 16. Output Short Circuit Operation
Figure 17. Input Current Short Circuit Operation
50
55
60
65
70
75
80
85
90
3.23.43.63.84.04.2
Vbat(V)
EFF
PLED
(%)
I
out
=20 mAI
out
=40 mA
I
out
=60 mA
I
out
=80 mA
I
out
=100 mA
Figure 18. Typical Efficiency
P1-P3P4-P6P7-P9P10-P12P13-P15

NCP5604AAGEVB

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ON Semiconductor
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