Datasheet LT3595A (Analog Devices) - 9
| Fabricante | Analog Devices |
| Descripción | 16 Channel Buck Mode LED Driver |
| Páginas / Página | 16 / 9 — OPERATION. Discontinuous Current Mode. Figure 1. Switching Waveforms. … |
| Formato / tamaño de archivo | PDF / 392 Kb |
| Idioma del documento | Inglés |
OPERATION. Discontinuous Current Mode. Figure 1. Switching Waveforms. APPLICATIONS INFORMATION. Inductor Selection
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LT3595A
OPERATION Discontinuous Current Mode
The LT3595A can drive a 10-LED string at 15mA LED VSW 20V/DIV current operating in continuous conduction mode using the recommended external components shown in the ap- plication circuit on page 1 of this data sheet. As current IL is further reduced, the regulator enters discontinuous 20mA/DIV conduction mode. The photo in Figure 1 details circuit operation driving ten LEDs at 10mA load. The inductor 3595A F01 400ns/DIV current reaches zero during the discharge phase and the VIN = 45V SW pin exhibits ringing. The ringing is due to the LC tank 10 LEDS AT 10mA circuit formed by the inductor in combination with the
Figure 1. Switching Waveforms
switch and diode capacitance. This ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions.
APPLICATIONS INFORMATION Inductor Selection Table 1. Inductor Manufacturers INDUCTANCE
A 100μH inductor is recommended for most LT3595A
RANGE (μH)
applications. Although small size and high effi ciency are
PART RELEVANT TO DIMENSIONS
major concerns, the inductor should have low core losses
VENDOR SERIES LT3595A (mm)
at 2MHz and low DCR (copper wire resistance). Some Coilcraft DO1605 100 to 680 5.4 × 4.2 × 1.8 www.coilcraft.com LPS4012 100 to 680 4 × 4 × 1.2 inductors that meet these criteria are listed in Table 1. An 1812FS 100 to 680 5.8 × 4.9 × 3.8 effi ciency comparison of different inductors is shown in MSS5131 100 to 390 5.1 × 5.1 × 3.1 Figure 2. Sumida CDC4D20 100 to 680 4.8 × 4.8 × 2 www.sumida.com 100 Toko D53LC 100 to 680 5.2 × 5.4 × 3 COILCRAFT 1812FS-104KLB COILCRAFT LPS4012-104MLB www.tokoam.com TOKO A915AY-101M TDK VLCF4020T 100 to 330 4 × 4 × 2 TDK VLCF4020T-101MR26 COILTRONICS SD3812-101 www.component. 95 COILTRONICS SD52-101 tdk.com Coiltronics SD3812 100 to 330 4 × 4 × 1.2 www.cooperet.com SD52 100 to 330 5.6 × 5.2 × 2 EFFICIENCY (%) Murata LQH32M 100 to 560 90 3.2 × 2.5 × 2 www.murata.com LQH43M 100 to 680 4.5 × 3.2 × 2
Capacitor Selection
8510 20 30 40 50 The small size of ceramic capacitors make them ideal for ILED (mA)* 3595A F02 LT3595A applications. Only X5R and X7R types should VIN = 45V L = 100μH 10 LEDS be used because they retain their capacitance over wider *ILED ADJUSTED WITH RSET voltage and temperature ranges than other types such as
Figure 2. Effi ciency Comparison of Different Inductors
Y5V or Z5U. Typically, 10μF capacitors on VIN and VCC are suffi cient. The output capacitor used across the LED 3595af 9
OPERATION Discontinuous Current Mode
The LT3595A can drive a 10-LED string at 15mA LED VSW 20V/DIV current operating in continuous conduction mode using the recommended external components shown in the ap- plication circuit on page 1 of this data sheet. As current IL is further reduced, the regulator enters discontinuous 20mA/DIV conduction mode. The photo in Figure 1 details circuit operation driving ten LEDs at 10mA load. The inductor 3595A F01 400ns/DIV current reaches zero during the discharge phase and the VIN = 45V SW pin exhibits ringing. The ringing is due to the LC tank 10 LEDS AT 10mA circuit formed by the inductor in combination with the
Figure 1. Switching Waveforms
switch and diode capacitance. This ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions.
APPLICATIONS INFORMATION Inductor Selection Table 1. Inductor Manufacturers INDUCTANCE
A 100μH inductor is recommended for most LT3595A
RANGE (μH)
applications. Although small size and high effi ciency are
PART RELEVANT TO DIMENSIONS
major concerns, the inductor should have low core losses
VENDOR SERIES LT3595A (mm)
at 2MHz and low DCR (copper wire resistance). Some Coilcraft DO1605 100 to 680 5.4 × 4.2 × 1.8 www.coilcraft.com LPS4012 100 to 680 4 × 4 × 1.2 inductors that meet these criteria are listed in Table 1. An 1812FS 100 to 680 5.8 × 4.9 × 3.8 effi ciency comparison of different inductors is shown in MSS5131 100 to 390 5.1 × 5.1 × 3.1 Figure 2. Sumida CDC4D20 100 to 680 4.8 × 4.8 × 2 www.sumida.com 100 Toko D53LC 100 to 680 5.2 × 5.4 × 3 COILCRAFT 1812FS-104KLB COILCRAFT LPS4012-104MLB www.tokoam.com TOKO A915AY-101M TDK VLCF4020T 100 to 330 4 × 4 × 2 TDK VLCF4020T-101MR26 COILTRONICS SD3812-101 www.component. 95 COILTRONICS SD52-101 tdk.com Coiltronics SD3812 100 to 330 4 × 4 × 1.2 www.cooperet.com SD52 100 to 330 5.6 × 5.2 × 2 EFFICIENCY (%) Murata LQH32M 100 to 560 90 3.2 × 2.5 × 2 www.murata.com LQH43M 100 to 680 4.5 × 3.2 × 2
Capacitor Selection
8510 20 30 40 50 The small size of ceramic capacitors make them ideal for ILED (mA)* 3595A F02 LT3595A applications. Only X5R and X7R types should VIN = 45V L = 100μH 10 LEDS be used because they retain their capacitance over wider *ILED ADJUSTED WITH RSET voltage and temperature ranges than other types such as
Figure 2. Effi ciency Comparison of Different Inductors
Y5V or Z5U. Typically, 10μF capacitors on VIN and VCC are suffi cient. The output capacitor used across the LED 3595af 9