MP24895 – STEP-DOWN WHITE-LED DRIVER WITH 6-36V INPUT VOLTAGE
MP24895 Rev. 1.0 www.MonolithicPower.com 9
8/6/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
OPERATION
Steady State
The MP24895 is a hysteretic-controlled, step-
down LED driver that is easily configured for
various applications with an input range from 6V
to 36V. The converter employs a high-side
current-sense resistor to detect and regulate the
LED current. The voltage across the current-
sense resistor is measured and regulated to
within 100mV±20mV.
The internal 1.275V reference voltage provides a
0.2V reference to enable the part and a 1.275V
pull-up voltage as current reference. When
V
EN
>0.2V, the output of the comparator goes high
and the other blocks are enabled.
A high-side resistor, R
SENSE
, senses the output
current. When the switch is on, R2 is shorted and
R1 sets the output current upper-threshold.
When the switch is off, R1 and R2 set the output
current lower-threshold, and the ratio of R1 and
R2 determines the current hysteresis.
Enable Control
Once Input voltage is applied, the internal 1.275V
reference is connected to EN/DIM pin through
pull up resistor. If the EN/DIM pin is left open, the
IC automatically starts up to the maximum
brightness. Adding a capacitor to this pin can
hereby program a soft-start time.
Applying an external voltage range from 0.2V to
1.25V to the EN/DIM pin linearly controls the
current-sense voltage reference from 0mV to
100mV for analog dimming.
Applying an external PWM voltage with an
amplitude of 1.25V to the EN/DIM pin achieves
PWM dimming. For additional information on the
flexible external PWM dimming method, please
refer to the “Selecting Dimming Control Mode”
section.
System Soft Start
The voltage on the EN/DIM pin is the inductor
current reference. An external capacitor from the
EN/DIM pin to ground provides a soft-start delay.
When V
IN
starts, internal voltage source charges
the capacitor from 0V to 1.25V for soft-start.
Dimming Control
MP24895 provides two dimming methods: PWM
dimming and DC analog dimming.
To use PWM dimming, apply a square wave to
the EN/DIM pin. To use analog dimming, apply a
0.3V-to-2.5V DC voltage to this pin.
