AN11470 Datasheet, PDF (10/25 Pages) NXP Semiconductors – Leadless Schottky diodes in a DC-to-DC step-up converter

NXP Semiconductors
AN11470
Leadless Schottky diodes in a DC-to-DC step-up converter
3. Demo PCB DC-to-DC step-up converter using very small Schottky
diodes
3.1 Hardware of the DC-to-DC step-up converter on demo PCB
To demonstrate the technical potential of NXP Semiconductors small package Schottky
diodes a demo PCB for an LED booster has been designed. It can be supplied with an
input voltage starting from 1.6 V. The input voltage is boosted based on a voltage up
converter structure as explained in the last chapter. A controller LT1618 from Linear
Technology Corporation is used for the switching task. It can work in constant current and
voltage control mode. LT1618 was chosen as an easy to handle device with a low pin
count. Figure 6 shows the schematic diagram of the demo PCB.
IN ₁
2
CON1
C1
10 μF
C2
100 nF
L1
LPS6225
10 μH
D1
PMEG2005BELD
D2
GND GND
GND _{IC1 VIN}
8
SHDN ₉
SW
PMEG2002AESF
7
3 ^ISP
R1
0.15 Ω
1 ^OUT
2
3
CON2
GND
n.c.
6
LT1618
ISN
2
IAdj
4
5
GND
FB
1
10
VC
C3
100 nF
GND GND
R2
332 kΩ
C4
10 μF
R3
124 kΩ
GND
GND
aaa-011230
Fig 6. Schematic diagram of LED booster demo PCB with Schottky diode
PMEG2005BELD (DFN1006D-2 / SOD882D) or
PMEG2002AESF (DSN0603-2 / SOD962)
The LT1618 works with a constant switching frequency of 1.4 MHz. This allows the usage
of small inductors and output capacitors. The operating voltage range is 1.6 V to 18 V. The
switch in the LT1618 is realized with a bipolar transistor. The controller can support an
output voltage control and an output current control. An inductance of 10 H is selected
for L1 and an output capacitor of 10 F. For the booster diode function two footprints (D1
and D2) are available. Only one of these diodes shall be assembled. One diode is
foreseen in an DFN1006D-2 (SOD882D) package with a size of
1 mm 0.6 mm 0.37 mm, the other assembly option is the smaller
DSN0603-2 (SOD962) package with a size of 0.6 mm  0.3 mm  0.3 mm. R1 is the
current sensing resistor. The current sensing voltage at R1 is limited to 50 mV by the
current control of LT1618. This leads to the following equation for the output current:
I_O = 50mV  R1
With R1 = 0.15 like on Figure 6, the output current is set to 333 mA. This is the suitable
current in case a 1 W power LED is foreseen as load for the demo PCB.
AN11470
Application note
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 22 April 2014
© NXP B.V. 2014. All rights reserved.
10 of 25