Datasheet
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. Figure 3 shows a C-R-C filter used
to reduce input ripple to less than 2mV
P-P
when driving
a 75mA load. Alternately, increasing C
IN
to 2.2µF or
4.7µF yields input ripple of 17mV
P-P
or 9mV
P-P
, respec-
tively, with only a small increase in footprint. The 1x
mode has very low input ripple.
PC Board Layout and Routing
The MAX1570 is a high-frequency switched-capacitor
voltage regulator. For best circuit performance, use a
solid ground plane and place C
IN
and C
OUT
as close
to the MAX1570 as possible. Also, place their ground
tails close together. Connect PGND and GND directly
under the IC to the exposed paddle, and connect C
IN
and C
OUT
as close as possible to PGND. The input
supply connections should be short; if this is not possi-
ble, an additional input supply filter capacitor (tantalum
or electrolytic) may be required. Refer to the MAX1570
EV kit for a good layout example.
Component Selection
Typical external component values are shown in Table
2 and Table 3.
Maximum power dissipation occurs around 4.2V on IN
and 4.0V at OUT with maximum load current.
At higher IN voltages this device switches to 1x mode
and power dissipation is lowered.
PVVVmA mW
DINOUT
=×
()
−
()
+
[]
×=15 04 120 324..
MAX1570
White LED Current Regulator with 1x/1.5x
High-Efficiency Charge Pump
_______________________________________________________________________________________ 9
LED1
LED2
LED3
LED4
LED5
4.7µF
PGNDGND
C1P C1N C2P C2N
1µF1µF
EN2
EN1
SET
IN
R
SET
1µF
V
IN
MAX1570
PWM INPUT
OUT
Figure 1. Dimming Using PWM Signal into EN1
LED1
LED2
LED3
LED4
LED5
4.7µF
PGNDGND
C1P C1N C2P C2N
1µF1µF
EN1
EN2
SET
IN
1µF
V
IN
MAX1570
OUT 0 TO 20mA/LED
C3
1µF
R1
14.3kΩ
R2
14.3kΩ
R
SET
9.09kΩ
PWM INPUT
0 TO 25V
Figure 2. Dimming Using Filtered-PWM Signal
LED1
LED2
LED3
LED4
LED5
4.7µF
PGNDGND
C1P C1N C2P C2N
1µF1µF
EN1
EN2
SET
IN
R
SET
2.2µF
2.2µF
V
IN
MAX1570
OUT
1Ω
Figure 3. C-R-C Filter Reduces Input Ripple
Chip Information
TRANSISTOR COUNT: 3187