LTC3577-4_15 Datasheet, PDF (33/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
OPERATION
Table 3. Recommended Inductors for Step-Down Switching Regulators
INDUCTOR TYPE
DB318C
D312C
DE2812C
L (μH)
4.7
3.3
4.7
3.3
4.7
3.3
MAX I_DC (A)
1.07
1.20
0.79
0.90
1.15
1.37
MAX DCR (Ω)
0.1
0.07
0.24
0.20
0.13*
0.105*
SIZE in mm (L × W × H)
3.8 × 3.8 × 1.8
3.8 × 3.8 × 1.8
3.6 × 3.6 × 1.2
3.6 × 3.6 × 1.2
3.0 × 2.8 × 1.2
3.0 × 2.8 × 1.2
CDRH3D16
CDRH2D11
CLS4D09
4.7
0.9
3.3
1.1
4.7
0.5
3.3
0.6
4.7
0.75
0.11
0.085
0.17
0.123
0.19
4 × 4 × 1.8
4 × 4 × 1.8
3.2 × 3.2 × 1.2
3.2 × 3.2 × 1.2
4.9 × 4.9 × 1
SD3118
SD3112
SD12
SD10
4.7
1.3
3.3
1.59
4.7
0.8
3.3
0.97
4.7
1.29
3.3
1.42
4.7
1.08
3.3
1.31
0.162
0.113
0.246
0.165
0.117*
0.104*
0.153*
0.108*
3.1 × 3.1 × 1.8
3.1 × 3.1 × 1.8
3.1 × 3.1 × 1.2
3.1 × 3.1 × 1.2
5.2 × 5.2 × 1.2
5.2 × 5.2 × 1.2
5.2 × 5.2 × 1.0
5.2 × 5.2 × 1.0
LPS3015
4.7
1.1
0.2
3.3
1.3
0.13
3.0 × 3.0 × 1.5
3.0 × 3.0 × 1.5
*Typical DCR
MANUFACTURER
Toko
www.toko.com
Sumida
www.sumida.com
Cooper
www.cooperet.com
Coil Craft
www.coilcraft.com
Table 4. Ceramic Capacitor Manufacturers
AVX
www.avxcorp.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay Siliconix
www.vishay.com
TDK
www.tdk.com
LED BACKLIGHT/BOOST OPERATION
Introduction
The LED driver uses a constant frequency, current mode
boost converter to supply power for up to 10 series LEDs.
As shown in Figure 11 the series string of LEDs is con-
nected from the output of the boost converter (BOOST) to
the I_LED pin. Under normal operation the boost converter
BOOST output will be driven to a voltage where the I_LED
pin regulates at approximately 300mV to 400mV. The I_LED
pin is a constant current sink that is programmed via I²C
“LED DAC register”. The LED can be further controlled
using I²C to program brightness levels and soft turn-on/
turn-off effects. See the “I²C Interface” section for more
information on programming the I_LED current. The boost
converter also includes an overvoltage protection feature
to limit the BOOST output voltage as well as variable slew
rate control of the SW pin to reduce EMI.
LED Boost Operation
The LED boost converter is designed for very high duty
cycle operation and can boost from 3V to 40V out for load
currents up to 20mA. The boost converter also features
overvoltage protection to protect the output in case of an
open circuit in the LED string. The overvoltage protection
threshold is set by adjusting R1 in Figure 11 such that:
BOOST(MAX) = 800mV • ^R1 + LED_ OV
10 • R2
where LED_OV is approximately 1.0V.
In the case of Figure 11 BOOST(MAX) is set to 40V for a
10-LED string.
Capacitor C3 provides soft-start, limiting the inrush cur-
rent when the boost converter is first enabled. C3 provides
feedback to the I_LED pin. This feedback limits the rise time
of output voltage and the inrush current while the output
capacitor, C2, is charging.
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