ncp5604 ON Semiconductor, ncp5604 Datasheet - Page 11

• Manufacturer Part Number: ncp5604
• Description: Current Mode Charge Pump Led Driver
• Manufacturer: ON Semiconductor

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.
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.
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.
A different analog approach, but more complex solution,
The current mirror can be largely improved by using an
V = 3.3 V
PWM
12 k
R1
GND
ENABLE
Figure 14. Basic Analog PWM Dimming Control
15 k
R2
NCP5604A, NCP5604B
http://onsemi.com
BC846BDW
GND
11
High Out
Figure 13. Basic Analog Dimming Control
GND
ENABLE
1
2 2
3
4
9
Q1
VBAT
EN
IREF
AGND
PGND
GND
1
2 2
3
4
9
VBAT
EN
IREF
AGND
PGND
VOUT
C2N
C3N
C2P
C3P
VOUT
C2N
C3N
C2P
C3P