Diodes PAM2810 - Manual (Page 6)

PAM2810
Document number: DSxxxxx Rev. 1 - 1
6 of 11
www.diodes.com
October 2012
© Diodes Incorporated
PAM2810
A Product Line of
Diodes Incorporated
Application Information
The PAM2810 is a 4-channel programmable white-LED driver. The matched current regulators each have a 100:1 ratio between the LEDx
outputs and the ISET current. The PAM2810 is capable of supplying 40mA per channel with the proper selection of the external RSET resistor,
with a total of 160mA output current available. LED brightness control of PAM2810 can be achieved with a PWM signal.
Output Current Capability
The PAM2810 is capable of providing up to 40mA per LED under an input voltage of 2.7V to 5.5V. An external resistor is used to set the output
current, as approximated with the following equation:
) I / V 22 . 1 ( * 100 R
LEDX SET
=
In order that the output currents could be regulated properly, the LEDx pin voltage(V
LEDX
) must be larger than the dropout voltage of the current
sink(V
DROPOUT
). To ensure the desired current is obtained, apply the following equation to determine the minimum input voltage:
V V V V
DROPOUT LEDX DIODE IN
≥ = −
V
DIODE
is the diode forward voltage, and some typical value of V
DROPOUT
can be found from the following table.
Table 1. I
LED
, R
SET
and V
DROPOUT
I
LED
R
SET
V
DROPOUT
10mA 12.7kΩ 40mV
20mA 6.2kΩ 80mV
30mA 4.3kΩ 120mV
40mA 3.2kΩ 150mV
PWM Brightness Control
Brightness control can be realized by applying a PWM signal to the EN pin. The constant current is set by the external resistor selected using the
RSET equation. The LED brightness is proportional to the duty cycle (D) of the PWM signal. The PWM frequency (f) should be limited to
accommodate the start-up time (50µs) of the device.
D * (1/f) >50µs
Table 2. PWM Frequency and Duty Cycle
Frequency Cycle
Duty-Cycle
Request
100Hz 10ms
100
5 . 0
>
1kHz 1ms
100
5
>
2kHz 500µs
100
10
>
4kHz 250µs
100
20
>
8kHz 125µs
100
40
>
10kHz 100µs
100
50
>
The maximum PWM frequency can be selected according to the table above.
If the PWM frequency is much less than 100Hz, flickering may be seen in the LEDs. For the PAM2810, zero duty cycle will turn off the LEDs and
a 50% duty cycle will result in an average ILED being half of the programmed LED current. For example, if RSET is set to program 20mA, a 50%
duty cycle will result in an average ILED of 10mA. RSET should be chosen not to exceed the maximum current capability of the device.