I'I'IPS'
MP4050 – NON-ISOLATED, HIGH BRIGHTNESS, LED DRIVER
MP4050 Rev.1.02 www.MonolithicPower.com 12
1/18/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
The peak current can be obtained as follow:
Peak
0.45V
IR1
R1 is the sense resistor.
Minimum Operating Frequency Limit
MP4050 incorporates minimum operating
frequency (22kHz) to eliminate the audible
noise when frequency is less than 20kHz.
When operating frequency is less than 22kHz,
the internal peak current regulator will decrease
the peak current value to keep the operating
frequency constant about 22kHz.
If the inductance value is too large to make the
operating frequency reach the minimum
operating frequency, the converter will enter the
CCM. And the converter works in DCM when
operating frequency is larger than 22kHz.
Minimum Off Time Limit
A minimum off time limit is implemented. During
the normal operation, the minimum off time limit
is 4.7us, and during the start up period, the
minimum off time limit is shortened gradually
from 18.8s, 9.4s to 4.7s (Shown as Figure
4). Each minimum off time keeps 128 switching
cycle. This soft start function enables safe start-
up.
≥18.4us ≥9.4us ≥4. 7us
Driver
128 switching cycle 128 switching cycle
Figure 4: tminoff at start-up
Thermal Shutdown (TSD)
To prevent MP4050 from any thermal damage,
MP4050 shuts down switching cycle when the
junction temperature exceeds 150C. As soon
as the junction temperature drops below 90C,
the power supply resumes operation. During
the thermal shutdown (TSD), the VCC is
discharged to VCCPRO, and then is re-charged
by the internal high voltage regulator.
Open Lamp Protection
If the PRO pin voltage (VPRO) is higher than VOVP
when MOSFET turns off, MP4050 stops
working and a re-start cycle begins. Open lamp
protection is hiccup mode. MP4050 monitors
the PRO pin voltage continuously and the VCC
voltage discharges and charges repeatedly.
MP4050 resumes work until the fault
disappears.
Short Lamp Protection
If the PRO pin voltage (VPRO) is lower than VUVP
when MOSFET turns off, MP4050 stops
working and a re-start cycle begins. Short lamp
protection is hiccup mode. MP4050 monitors
the PRO pin voltage continuously and the VCC
voltage discharges and charges repeatedly.
MP4050 resumes work until the fault
disappears.
Leading Edge Blanking
There are parasitic capacitances in the circuit
which can cause high current spike during the
turn-on of the internal MOSFET. In order to
avoid the premature termination of the
switching pulse, an internal Leading Edge
Blanking (LEB) unit is employed. During the
blanking time, the current comparator is
disabled and blocked from turning off the
internal MOSFET. Figure 5 shows the leading
edge blanking.
TLEB
VLimit
t
Figure 5: Leading Edge Blanking (LED)