HV9961 datasheet(7/20 Pages) MICROCHIP

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DS20005588B-page 7

HV9961

FIGURE 3-1:

Typical Output

Characteristic of an HV9961 LED Driver.

The short-circuit protection comparator trips when the

voltage at CS exceeds 0.44V. When this occurs, the

short-circuit gate off-time THICCUP = 400 µs is

generated to prevent the staircasing of the inductor

current and, potentially, its saturation due to insufficient

output voltage. The typical short-circuit inductor current

is shown in the waveform of Figure 3-2.

FIGURE 3-2:

Short-circuit Inductor

Current.

A leading-edge blanking delay is provided at CS to

prevent false triggering of the current feedback and the

short-circuit protection.

3.4

Linear Dimming

When the voltage at LD falls below 1.5V, the internal

275 mV reference to the constant-current feedback

becomes overridden by VLD x 0.185. As long as the

current in the inductor remains continuous, the LED

current is given by Equation 3-3. However, when VLD

falls below 150 mV, the gate output becomes disabled.

The gate signal recovers when VLD exceeds 200 mV. It

is required in some applications to use the same

brightness control signal input to shut off the lamp. The

typical linear dimming response is shown in Figure 3-3.

FIGURE 3-3:

Typical Linear Dimming

Response of an HV9961 LED Driver.

The linear dimming input could also be used for

“mixed-mode” dimming to expand the dimming ratio. In

such case, a pulse-width modulated signal with an

amplitude below 1.5V should be applied to LD.

3.5

Input Voltage Regulator

The HV9961 can be powered directly from an

8 VDC–450 VDC supply through its VIN input. When this

voltage is applied at the VIN pin, the HV9961 maintains

a constant 7.5V level at VDD. This voltage can be used

to power the IC and external circuitry connected to VDD

within the rated maximum current or within the thermal

ratings of the package, whichever limit is lower. The

VDD pin must be bypassed by a low ESR capacitor to

provide a low-impedance path for the high-frequency

current of the gate output. The HV9961 can also be

powered through the VDD pin directly with a voltage

greater than the internally regulated 7.5V, but less than

12V.

Despite the instantaneous voltage rating of 450V,

continuous voltage at VIN is limited by the power

dissipation in the package. For example, when HV9961

draws IIN = 2.5 mA from the VIN input, and the 8-pin

SOIC package is used, the maximum continuous

voltage at VIN is limited to the value shown in

Equation 3-5.

EQUATION 3-5:

IN = 170VDC

HV9961

HV9910B

2030405060

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

Output Voltage (V)

400µs

0.44V/R

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

LD (V)

LD Response Characteristics

VIN MAX



TJMAX



–

R JA



IIN



--------------------------------

396V

Where:

Ambient temperature: TA = 25°C

Maximum working junction temperature: TJ(MAX) = 125°C

Junction-to-ambient thermal resistance:

Rθ,JA = 101°C/W

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