MIC2845A datasheet(13/18 Pages) MICREL

13 / 18 page

Micrel Inc.

MIC2845A

April 2010

M9999-041210-C

Figure 7. PWM Signal at 20% Duty Cycle (I

avg = 4mA)

Figure 8. PWM Signal at 50% Duty Cycle (Iavg = 10mA)

Figure 9. PWM Signal at 80% Duty Cycle (Iavg = 16mA)

Figure 10. PWM Signal at 100% Duty Cycle (Iavg = 20mA)

High Current Parallel Operation

Figure 11. Six Channel (Parallel) Application Circuit

The linear drivers are independent of each other and can

be used individually or paralleled to provide larger

current. A single LED can be driven with all 6 linear

drivers by connecting D1 through D6 together with the

cathode of the LED as shown in Figure 11. This will

generate a current 6 times the LED current setting and

can be used for higher current LEDs such as those used

in flash or torch applications. The current is set by the

RSET resistor, and can be calculated by the following

equation.

ILED (mA) = 6 * 410 * D / RSET (kΩ).

D is the duty cycle of the LED current during PWM

dimming. When the device is fully on the duty cycle

equals 100% (D = 1). Figure 12 shows the response

time of the six paralleled linear drivers to the enable

signal, while Figure 13 shows the turn off response. With

a RSET resistor of 1.65k, each linear driver is set to

250mA, with all 6 linear drivers connected in parallel, the

MIC2843 is capable of driving a total current of 1.5A.

MIC2845A Datasheet(PDF) 13 Page - Micrel Semiconductor