HV9963NG-G Supertex, HV9963NG-G Datasheet - Page 10

• Manufacturer Part Number: HV9963NG-G
• Description: LED Drivers Clsd Loop LED driver W/ Enhanced PWM DIM
• Manufacturer: Supertex

Specifications of HV9963NG-G

• Operating Supply Voltage: 40 V
• Maximum Power Dissipation: 1000 mW
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-16
• Minimum Operating Temperature: - 65 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 filter capacitor should be
large enough so that it can absorb the inductor energy with-
out significant change of the voltage across it. If the capaci-
tor voltage change is significant, 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 11μA 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:
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
Figure 6: PWM Dimming with dimming on-time equal to
I
PWMD
INDUCTOR
one switching time period with the HV9963
C
I
HCP
LED
=
11µA • T
2V
HCP
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
I
I
O
L
(SS)
(SS)
10
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.
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:
Where I
In the case of the HV9963, (T
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:
If the short circuit occurs when the PWM dimming signal is
already high, the time to detect will be:
Over Voltage Protection
The HV9963 provides hysteretic over voltage protection
allowing the IC to recover in case the LED load is discon-
nected momentarily.
P
SAT
t
t
DETECT1
DETECT1
RS
●
is the saturation current of the disconnect FET.
≥
Tel: [phone]
I
SAT
= t
= t
BLANK
DELAY
2
• R
S
t
≈ 250ns(max)
HICCUP
+ t
• (T
DELAY
●
FAULT
FAULT
www.supertex.com
≈ 1050ns(max)
+ T
+ T
OFF
OFF
)
) is 550ns (max).
HV9963