MXHV9910

6

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R01

Figure 3 MXHV9910 Waveforms (From Application Circuit in Figure 6)

2.2.1 Input Voltage Regulator

The MXHV9910 has an internal voltage regulator that

pin is the internal regulator output pin and must be

bypassed by a low ESR capacitor, typically 0.1

μF, to

provide a low impedance path for high frequency

switching noise.

The MXHV9910 driver does not require the bulky

start-up resistors typically needed for off-line

controllers. An internal voltage regulator provides

sufficient voltage and current to power the internal IC

and can be used as bias voltage for external circuitry.

The internal voltage regulator can by bypassed by

slightly higher than the internal regulator’s maximum

output voltage. This feature reduces power dissipation

of the integrated circuit and is more suitable in isolated

applications where an auxiliary transformer winding

the integrated circuit quiescent current, which is

0.6mA maximum, plus the gate driver current. The

gate driver current is dependant on the switching

frequency and the gate charge of the external power

MOSFET.

The following equation can be used to approximate

frequency.

2.2.2 Current Sense Resistor

The peak LED current is set by an external current

sense resistor connected from the CS pin to ground.

The value of the current sense resistor is calculated

based on the desired average LED current, the current

sense threshold, and the inductor ripple current.

The inductor is typically selected to be large enough to

keep the ripple current (the peak-to-peak difference in

the inductor current waveform) to less than 30% of the

average LED current. Factoring in this ripple current

requirement, the current sense resistor can be

determined by:

Where:

The power dissipation rating of the sense resistor can

be found with the following formula:

CH1:

50mA/div

CH2:

CH3:

5mV/div x 10

Time Scale: 5

μs/div

Max 77mA

10V/div

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