HV9963 Datasheet, PDF(10/12 Page) Supertex, Inc – Closed Loop LED Driver with Enhanced PWM Dimming

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

HV9963 Datasheet, PDF (10/12 Pages) Supertex, Inc – Closed Loop LED Driver with Enhanced PWM Dimming

◁

HV9963

PWMD

ILED

IINDUCTOR

IO(SS)

IL(SS)

timer is started. Once the timing is complete, the converter

attempts to restart. If the fault condition still persists, the con-

verter shuts down and goes through the cycle again. If the

fault condition is cleared (due to a momentary output short)

the converter will start regulating the output current normally.

This allows the LED driver to recover from accidental shorts

without having to reset the IC.

Figure 6: PWM Dimming with dimming on-time equal to

one switching time period with the HV9963

Note that disconnecting the LED load during PWM dimming

causes the energy stored in the inductor to be dumped into

the output capacitor. The chosen ï¬lter capacitor should be

large enough so that it can absorb the inductor energy with-

out signiï¬cant change of the voltage across it. If the capaci-

tor voltage change is signiï¬cant, it would cause a turn-on

spike in the inductor current when PWMD goes high.

Fault Conditions and Hiccup Timer (OVP, HCP)

The HV9963 is a robust controller which can protect the

LEDs and the LED driver in case of fault conditions. The

HV9963 includes both open LED protection and output short

circuit protection. In both cases, the HV9963 shuts down

and attempts a restart. The hiccup time is programmed by

the capacitor at the HCP pin.

When a fault condition is detected, both GATE and FLT

outputs are disabled and the COMP, SS and HCP pins are

pulled to GND. Once the voltage at the HCP pin falls be-

low 0.1V and the fault condition(s) have disappeared, the

capacitor at the HCP pin is released and is charged slowly

by a 11Î¼A current source. Once the capacitor is charged to

2.1V, the COMP and SS pins are released and GATE and

FLT pins are allowed to turn on. Then, the converter will go

into a soft-start mode ensuring a smooth recovery for the

LED current.

Hiccup Timer (HCP)

The value of the capacitor required for a given hiccup time

is given by:

CHCP =

11ÂµA â¢ THCP

Short Circuit Protection

When a short circuit condition is detected (output current be-

comes higher than twice the steady state current), the GATE

and FLT outputs are pulled low. As soon as the disconnect

FET is turned off, the output current goes to zero and the

short circuit condition disappears. At this time, the hiccup

Note that the power rating of the LED sense resistor has to

be chosen properly if it has to survive a persistent fault con-

dition. The power rating can be determined using:

PRS â¥

ISAT2 â¢ RS â¢ (TFAULT + TOFF )

tHICCUP

Where ISAT is the saturation current of the disconnect FET.

In the case of the HV9963, (TFAULT + TOFF) is 550ns (max).

False Triggering of the Short Circuit Compara-

tor During PWM Dimming

During PWM dimming, the parasitic capacitance of the LED

string might cause a spike in the output current when the

disconnect FET is turned on. If this spike is detected by the

short circuit comparator, it will cause the IC to falsely detect

an over current condition and shut down.

In the HV9963, to prevent these false triggers, there is a built

in 500ns blanking network for the short circuit comparator.

This blanking network is activated when the PWMD input

goes high. Thus, the short circuit comparator will not see the

spike in the LED current during the PWM dimming turn-on

transition. Once the blanking timer is completed, the short

circuit comparator will start monitoring the output current.

Thus, the total delay time for detecting a short circuit will

depend on the condition of the PWMD input.

If the output short circuit exists before the PWM dimming

signal goes high, the total detection time will be:

tDETECT1 = tBLANK + tDELAY â 1050ns(max)

If the short circuit occurs when the PWM dimming signal is

already high, the time to detect will be:

tDETECT1 = tDELAY â 250ns(max)

Over Voltage Protection

The HV9963 provides hysteretic over voltage protection

allowing the IC to recover in case the LED load is discon-

nected momentarily.

â 1235 Bordeaux Drive, Sunnyvale, CA 94089 â Tel: 408-222-8888 â www.supertex.com

▷