HV9982K6-G 查看數據表（PDF） - Supertex Inc

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HV9982K6-G

Three-Channel, Closed-Loop, Switch Mode LED Driver IC

Supertex Inc 

HV9982

Table 1: S1 and S2 control logic

S1 S2 PWMD output

00

The output will follow PWMD input signal

01

1

0

Input DC zero volt corresponds to 100% duty

cycle output

1

1

Input DC two volt corresponds to 100% duty

cycle output

When S1 is high and the HV9982 is operating in the analog

control of PWM dimming mode, the PWM dimming frequen-

cy is set by a capacitor connected at the RAMP pin. The

RAMP frequency range is 100Hz - 1.0kHz and the capacitor

can be selected as:

f(Hz) = 1.0µS

C

RAMP

(Note: In the following description of the PWM dimming

performance the PWMD signals refer to the internal

PWM dimming signal and not to the signal applied at

the PWMD pins).

When the PWM signal is high, the GATE and FLT pins are

enabled and the output of the transconductance opamp is

connected to the external compensation network. Thus,

the internal amplifier controls the output current. When the

PWMD signal goes low, the output of the transconductance

amplifier is disconnected from the compensation network.

Thus, the integrating capacitor maintains the voltage across

it. The GATE is disabled, so the converter stops switching

and the FLT pin goes low, turning off the disconnect switch.

The output capacitor of the converter determines the PWM

dimming response of the converter, since it has to get

charged and discharged whenever the PWMD signal goes

high or low. In the case of a buck converter, since the in-

ductor current is continuous, a very small capacitor is used

across the LEDs. This minimizes the effect of the capacitor

on the PWM dimming response of the converter. However,

in the case of a boost converter, the output current is dis-

continuous and a very large output capacitor is required to

reduce the ripple in the LED current. Thus, this capacitor will

have a significant impact on the PWM dimming response.

By turning off the disconnect switch when PWMD goes low,

the output capacitor is prevented from being discharged and

thus the PWM dimming response of the boost converter Im-

proves dramatically.

Fault Conditions

The HV9982 is a robust controller which can protect the

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

HV9982 includes both open LED protection and output short

circuit protection. In both cases, the HV9982 shuts down

and attempts a restart. The hiccup time can be programmed

by a single external capacitor at the SKIP pin.

During start-up or when a fault condition is detected, both

GATE and FLT outputs are disabled, the COMP pins and

SKIP pins are pulled to GND. Once the voltage at the SKIP

pin falls below 0.1V and the fault condition(s) have disap-

peared, the capacitor at the SKIP pin is released and is

charged slowly by a 10μA current source. Once the capacitor

is charged to 5.0V, the COMP pins are released and GATE

and FLT pins are allowed to turn on. If the hiccup time is long

enough, it will ensure that the compensation networks are

all completely discharged and that the converters start at

minimum duty cycle.

The hiccup timing capacitor can be programmed as:

CRAMP =

10µA • tHICCUP

4.9V

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

timer is started (Fig. 3). Once the timing is complete, the

converter attempts to restart. If the fault condition still per-

sists, the converter 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.

During short circuit conditions, there are two conditions that

determine the hiccup time.

The first is the time required to discharge the compensation

capacitors. Assuming a pole-zero R-C network at the COMP

pin (series combination of RZ and CZ in parallel with CC),

tCOMP,n = 3 • RZn • CZn

Note that disconnecting the LED load during PWM dimming

causes the energy stored in the inductor to be dumped into

the output capacitor. The filter capacitor should be chosen

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

out significant change to the voltage across it.

where n refers to the channel number.

In case the compensation networks are only type 1 (single

capacitor), then:

tCOMP,n = 3 • 300Ω • CZn

8

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