LED5000PHR STMicroelectronics, LED5000PHR Datasheet - Page 20

• Manufacturer Part Number: LED5000PHR
• Description: Current & Power Monitors & Regulators 3A monolithic Conv 850kHz Synch
• Manufacturer: STMicroelectronics

Specifications of LED5000PHR

• Rohs: yes
• Product: Current Regulators
• Supply Voltage - Max: 48 V
• Supply Voltage - Min: 5.5 V
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Package / Case: HPSO-8
• Accuracy: +/- 3 %
• Input Voltage Range: 5.5 V to 48 V
• Output Current: 23 uA
• Sensing Method: High or Low Side
• Supply Current: 1.7 mA

Application notes - buck conversion
5.8
20/51
The cut-off frequency and the phase margin are:
Equation 22
Dimming operation
The dimming input disables the switching activity, masking the PWM comparator output.
The inductor current dynamic performance when dimming input goes high depends on the
designed system response. The best dimming performance is obtained by maximizing the
bandwidth and phase margin, when possible.
As a general rule, the output capacitor minimization improves dimming performance.
Figure 12. dimming operation example
In fact, when dimming enables the switching activity, a small capacitor value is fast charged
with low inductor value. As a consequence, the LEDs current rising edge time is improved
and the inductor current oscillation reduced. An oversized output capacitor value requires
extra current for fast charge so generating an inductor current overshoot and oscillations.
The switching activity is prevented as soon as the dimming signal goes low. Nevertheless,
the LED current drops to zero only when the voltage stored in the output capacitor goes
below a minimum voltage determined by the selected LEDs. As a consequence, a big
capacitor value makes the LED current falling time worse than a smaller one.
The LED5000 embeds dedicated circuitry to improve LED current rising edge time.
Doc ID 023951 Rev 1
f
C
=
65 kHz
pm
=
66
LED5000
AM13496v1