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MP4689DN-LF-Z

P1-P3P4-P6P7-P9P10-P10
MP4689 – 100V INPUT, 1A HIGH POWER LED DRIVER
MP4689 Rev. 1.01 www.MonolithicPower.com 7
4/14/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
OPERATION
Hysteresis Current Control with Adaptive
Threshold Adjustment
MP4689 operates in a hysteresis current control
mode to regulate the LED current accurately.
FB pin is the sensed voltage of LED current
across the sensing resistor. The power
MOSFET is turned on and remains on until FB
pin rises to 215mV. The power MOSFET is
turned off and remains off until FB pin falls to
185mV. The two thresholds of 215mV and
185mV are adaptive adjusted to compensate all
the circuit delays so that the LED current is
regulated very accurately with 200mV average
value at FB pin.
Enable Control
The MP4689 has a dedicated enable control pin
(EN) with the positive logic. Its falling threshold
is a precision 1.2V, and its rising threshold is
1.5V (300mV higher).
When floating, EN is pulled up to about 3.0V by
an internal 1µA current source so it is enabled.
To pull it down, over 1µA current capability is
needed.
Floating Driver and Bootstrap Charging
The floating power MOSFET driver is powered
by an external bootstrap capacitor. This floating
driver has its own UVLO protection. This
UVLO’s rising threshold is 2.2V with a threshold
of 150mV.
The bootstrap capacitor is charged and
regulated to about 5V by the dedicated internal
bootstrap regulator.
In case the internal circuit does not have
sufficient voltage and the bootstrap capacitor is
not well charged, extra external circuitry can be
used to ensure the bootstrap voltage is in the
normal operational region. Refer to External
Bootstrap Diode in Application section.
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) is implemented
to protect the chip from operating at insufficient
supply voltage. The UVLO rising threshold is
about 4.0V while its falling threshold is a
consistent 3.65V.
Thermal Shutdown
Thermal shutdown is implemented to prevent
the chip from operating at exceedingly high
temperatures. When the silicon die temperature
is higher than its upper threshold, it shuts down
the whole chip. When the temperature is lower
than its lower threshold, the chip is enabled
again.
LED Short Protection
The LED current is well regulated with FB pin
voltage at 200mV. As long as the LED sensing
resistor is not failed, the output current is within
limitation. If the LED sensing resistor is failed or
the output is shorted to GND directly, the FB pin
voltage is low even the power MOSFET is
turned on. The power MOSFET will be shut off
if such failure time is longer than 10us. MP4689
will retry the operation after about 300s delay.
The power MOSFET current is also accurately
sensed via a current sense MOSFET. If the
current is over 2.5A, the IC is shut down. This
offers extra protection under output short
conditions.
MP4689 – 100V INPUT, 1A HIGH POWER LED DRIVER
MP4689 Rev. 1.01 www.MonolithicPower.com 8
4/14/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the LED Current
The LED current I
LED
is set using a sensing
resistor R
FB
, which is in series with the LEDs
and connected to GND. The voltage on the
sensing resistor R
FB
is connected to FB pin.
FB
LED
FB
V
I
R
For example, for a 700mA LED current, R
FB
is
287m.
Inductor Selection and Frequency Setting
The inductor L
O
is required to supply a constant
current to the LED. The inductor value is related
to the switching frequency f
s
setting:
OUT IN OUT
s
8
IN IN LED
V(VV)
f
V(810 V L15%I)


Where, V
IN
is the input voltage, V
OUT
is the
output voltage to drive the LEDs. A larger value
inductor will result in smaller switching
frequency.
The peak inductor current is about:
8
IN
LP LED
LED
410 V
II( 1.075)
LI


Choose an inductor that will not saturate under
the maximum inductor peak current and the
switching frequency under 2MHz.
Output Rectifier Diode
The output rectifier diode supplies the current to
the inductor when the high-side switch is off. To
reduce losses due to the diode forward voltage
and recovery times, use a Schottky diode.
The RMS current through the diode is about:
OUT
DLED
IN
V
II 1
V

Choose a diode whose maximum reverse
voltage rating is greater than the maximum
input voltage, and whose current rating is
greater than the maximum diode current.
Input Capacitor C
IN
The input current to the step-down converter is
discontinuous, therefore a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance especially under high switching
frequency applications.
The RMS current through the input capacitor is
about:
OUT
DLED
IN
V
II
V

’
With low ESR capacitors, the input voltage
ripple can be estimated by:
OUT OUT
LED
IN
sIN IN IN
VV
I
V1
fC V V




Choose the input capacitor with enough RMS
current rating and enough capacitance for small
input voltage ripple.
When electrolytic or tantalum capacitors are
applied, a small, high quality ceramic capacitor,
i.e. 0.1F, should be placed as close to the IC
as possible.
Output Capacitor C
OUT
The output capacitor (C
OUT
) is not necessary for
MP4689. The LED current ripple (peak-to-peak
value) is about 15% of the LED DC current.
Output capacitor can be used to further reduce
the LED current ripple. Low ESR capacitors are
preferred to keep the output voltage ripple low
so that the AC ripple current through the LEDs
is small. The output voltage ripple can be
estimated by:
OUT OUT
OUT ESR
SO IN S OUT
VV
1
V1R
fL V 8fC








Where R
ESR
is the equivalent series resistance
(ESR) value of the output capacitor.
MP4689 – 100V INPUT, 1A HIGH POWER LED DRIVER
MP4689 Rev. 1.01 www.MonolithicPower.com 9
4/14/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the LED driver. In below cases, an
external BST diode is recommended from the
5V to BST pin:
There is a 5V rail available in the system;
VIN is no greater than 5V;
VOUT is between 3.3V and 5V;
This diode is also recommended for high duty
cycle operation (when V
OUT
/V
IN
>65%) and very
high frequency (over 1.5MHz) applications.
The bootstrap diode can be a low cost one
such as IN4148 or BAT54.
MP4560
SW
BS
5V
MP4689
Figure 2—External Bootstrap Diode
Layout Consideration
It is essential to place the input decoupling
capacitor, catch diode and the MP4689 (VIN pin,
SW pin and PGND) as close as possible, with
traces that are very short and fairly wide. This
can help to greatly reduce the voltage spike on
SW node, and lower the EMI noise level as well.
Try to run the feedback trace as far from the
inductor and noisy power traces as possible. It
is often a good idea to run the feedback trace
on the side of the PCB opposite of the inductor
with a ground plane separating the two.
To help to improve the thermal conduction, a
grid of thermal vias can be created right under
the exposed pad. It is recommended that they
be small (15mil barrel diameter) so that the hole
is essentially filled up during the plating process,
thus aiding conduction to the other side. Too
large a hole can cause ‘solder wicking’
problems during the reflow soldering process.
The pitch (distance between the centers) of
several such thermal vias in an area is typically
40mil.
P1-P3P4-P6P7-P9P10-P10

MP4689DN-LF-Z

Mfr. #:
Buy MP4689DN-LF-Z
Manufacturer:
Monolithic Power Systems (MPS)
Description:
LED Lighting Drivers 100V 1A High Power LED Driver
Lifecycle:
New from this manufacturer.
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