MP3362

– SINGLE-STRING, 3V MINIMUM Vin, 36V BOOST LED DRIVER

MP3362 Rev. 1.1

www.MonolithicPower.com

12

2/22/2023

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Calculate the LED current with Equation (1):

FB

LED

FB

V

I

Duty

R

=

(1)

Where VFB is the FB voltage (about 200mV), RFB

is the feedback resistor, and Duty is the PWM

signal duty.

Protections

The

MPQ3326

’s protections include under-

voltage lockout (UVLO), over-voltage protection

(OVP), over-current protection (OCP), short LED

protection, short FB-to-GND protection, short

inductor/diode protection, and thermal protection.

Under-Voltage Lockout (UVLO)

The MP3362 integrates VIN under-voltage lockout

(UVLO) protection. The internal circuit does not

work until VIN reaches the UVLO rising threshold.

Over-Voltage Protection (OVP)

Over-voltage protection (OVP) is detected by

sensing the voltage on the OVP pin. If the OVP

pin’s voltage reaches its high threshold, OVP is

triggered and the IC stops switching. The IC tries

to recover when the OVP

pin’s voltage drops to its

low threshold.

Short Load Protection

Under short load conditions, a large short current

is detected by the FB sense resistor. If the FB-

sensed voltage exceeds 600mV for 20 switching

cycles, short load protection is triggered and the

IC stop switching. The IC resumes when the short

disappears.

High voltage appears on the FB pin under short

load

conditions.

Figure

3

shows

additional

components that are required to protect the FB pin

from damage.

FB

D1

RFB

FB

D1

RFB

R1

a)

b)

Figure 3: Short Load Protection for the FB Pin

Note that there is a short loop from the input to

GND under short load conditions. Use a fuse or an

external circuit to cut off the short loop.

OVP Pin Under-Voltage Protection (UVP)

If the OVP

pin’s voltage drops below 60mV for

10µs during normal operation, under-voltage

protection (UVP) is triggered, and the IC stops

switching. This protection is blanked during soft

start.

Over-Current

Protection

(OCP)

(Short

Inductor/ Diode Protection)

The MP3362 implements cycle-by-cycle current

limit protection. If there is an inductor or diode

short, and the MOSFET

’s current exceeds the

latch-off current limit value (typically 6.5A) for

seven consecutive cycles, over-current protection

(OCP) is triggered. The IC stop switching and

resumes when the short disappears.

Short FB to GND Protection

If the FB voltage drops below 50mV and the

COMP saturation lasts for 20ms, the IC stops

switching. The IC resumes normal operation when

the short disappears.

Thermal Protection

Thermal shutdown prevents the MP3362 from

operating at exceedingly high temperatures. If the

die temperature exceeds the upper threshold (TSD

= 170°C), COMP is pulled low. The IC resumes

normal operation once the die temperature drops

below its lower threshold. The hysteresis is about

20°C.