Rainbow Electronics MAX1574 - Manual (Page 7)

Applications Information
Driving Fewer than Three LEDs
When driving fewer than three LEDs, connect any unused
LED_ directly to IN (Figure 3). When connected in this
manner, the corresponding LED driver is disabled.
Driving Camera Strobes/Flashes
The MAX1574’s 180mA output capability makes it suit-
able for driving white LED camera strobes/flashes. For
example, the typical operating circuit drives a 3-LED
flash module with up to 60mA/LED. To ensure 180mA
total drive capability at low input voltages, increase C1
to 0.47µF.
To drive fewer or more LEDs with regulated total cur-
rent up to 180mA or to reduce the number of connect-
ing wires, short LED1, LED2, and LED3 together. When
connected this way, some LED modules have good
LED-to-LED forward-voltage matching, while others
may require individual ballast resistors. It is a good
idea to keep the ballast resistance as low as practical
for reasonable matching because high-ballast resis-
tance reduces the output drive capability due to the
higher V
OUT requirement.
Input Ripple
For LED drivers, input ripple is more important than out-
put ripple. Input ripple depends on the source supply’s
impedance. Adding a lowpass filter to the input further
reduces input ripple. Alternatively, increasing C
IN to
2.2µF cuts input ripple in half with only a small increase in
footprint. The 1x mode always has very low input ripple.
Component Selection
Use only ceramic capacitors with an X5R, X7R, or better
dielectric. See Table 1 for a list of recommended parts.
PC Board Layout and Routing
The MAX1574 is a high-frequency switched-capacitor
voltage regulator. For best circuit performance, use a
solid ground plane and place C
IN
, C
OUT
, and C1 as
close to the MAX1574 as possible. Refer to the
MAX1574 evaluation kit for an example.
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
_______________________________________________________________________________________ 7
Table 1. Recommended Components
COMPONENT
DESIGNATION
VALUE MANUFACTURER PART NUMBER DESCRIPTION
Taiyo Yuden JMK107BJ105KA 1µF ±10%, 6.3V X5R ceramic capacitors (0603)
C IN , C OUT 1µF
TDK C1005X5R0J105M 1µF ±20%, 6.3V X5R ceramic capacitors (0402)
Taiyo Yuden JMK105BJ224KV 0.22µF ±10%, 6.3V X5R ceramic capacitor (0402)
0.22µF
TDK C1005X5R0J224K 0.22µF ±10%, 6.3V X5R ceramic capacitor (0402)
Taiyo Yuden JMK105BJ474KV 0.47µF ±10%, 6.3V X5R ceramic capacitor (0402)
C1
0.47µF
TDK C1005X5R0J474K 0.47µF ±10%, 6.3V X5R ceramic capacitor (0402)
Nichia NSCW215T White LEDs
D1, D2, D3 —
Citizen CL-470S White LED flash module
Kamaya
R SET As Required
Panasonic
— 1% resistor