MP23701 – 24V, 2A, 1.5MHZ, SYNCHRONOUS, STEP-DOWN, LED DRIVER

MP23701 Rev. 1.0

www.MonolithicPower.com

11

3/22/2019

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Analog Dimming

Apply a DC signal on EN/DIM to dim the

MP23701 in analog dimming mode. When the

voltage on EN/DIM is lower than VADIM_MIN, the

LED current is regulated to the minimum scale.

When the voltage on EN/DIM is between

VADIM_MIN and VADIM_MAX, the LED current

changes from the minimum scale to the full

scale of the LED current. If the voltage on

EN/DIM is higher than VADIM_MAX, the maximum

LED current is regulated.

Figure 3 shows the analog dimming curve. Due

to the hysteretic of the EN/DIM on/off threshold,

the chip remains at the minimal LED current

longer at the VEN/DIM falling edge until VEN/DIM is

lower than VEN_OFF. The dimming curve is the

same as in the linear dimming range.

Figure 3: Analog Dimming Curve

Open LED

If the LED is open without a feedback signal,

the MP23701 works at the maximum duty cycle,

and the output voltage rises up almost to the

input voltage. Every power component operates

at a safe state.

LED Short-Circuit Protection (SCP)

The MP23701 integrates LED short-circuit

protection (SCP) circuitry. There are several

features protecting the MP23701 from damage

when an LED short circuit occurs.

The MP23701 uses a cycle-by-cycle current

limit to restrict the maximum current of the

inductor. A protection mechanism monitors the

FB level though an internal R-C filter. Once the

FB level rises up to VFB_BURST_AL, the chip stops

switching until the FB level drops to a lower

value, and the system works in burst mode.

In the worst-case scenario, the LED is shorted

to GND. If the cycle-by-cycle current-limit

function cannot clamp the current overshoot

sufficiently, then the current through both the

HS-FET and LS-FET is also monitored by the

over-current detector inside the chip. If this

current is higher than the short-circuit threshold

(IOCP), the MP23701 treats this as a short-circuit

condition.

When an over-current condition or short-circuit

condition is detected, the MP23701 turns off

both the HS-FET and LS-FET for 2.4ms and

restarts. During this period, VCOMP is pulled

down to ground, so the restart from the fault

condition is also done with a soft start.

Thermal Protection

NTC provides LED thermal protection. An NTC

resistor

used

to

monitor

the

ambient

temperature can be connected to NTC directly.

There is an internal current source flowing out

of

NTC.

The

corresponding

voltage

is

generated on the external NTC resistor and the

LED current changes (see Figure 4).

Figure 4: NTC Curve

The NTC resistance value drops when the

ambient temperature rises up. If the NTC

voltage drops below VSD_NTC, the switching

stops completely, and the LED current drops to

0A, so the LED lamp can be shut down by

pulling NTC down.

Additionally, to protect against any lethal

thermal damage, when the inner temperature

exceeds the over-temperature protection (OTP)

threshold, the MP23701 uses thermal shutdown

to shut down the switching cycle until the

temperature drops to its lower threshold.