MAX1570 Ver la hoja de datos (PDF) - Maxim Integrated
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MAX1570 Datasheet PDF : 11 Pages
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White LED Current Regulator with 1x/1.5x
High-Efficiency Charge Pump
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 2mVP-P when driving
a 75mA load. Alternately, increasing CIN to 2.2µF or
4.7µF yields input ripple of 17mVP-P or 9mVP-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 CIN and COUT 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 CIN
and COUT 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.
1µF
1µF
C1P C1N C2P C2N
IN
VIN
1µF
OUT
4.7µF
EN2
PWM INPUT
EN1
SET
RSET
MAX1570
LED1
LED2
LED3
LED4
LED5
GND
PGND
Figure 1. Dimming Using PWM Signal into EN1
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.
[( ) ] ( ) PD = 1.5 × VIN − VOUT + 0.4V × 120mA = 324mW
At higher IN voltages this device switches to 1x mode
and power dissipation is lowered.
1µF
1µF
C1P C1N C2P C2N
IN
VIN
1µF
OUT
0 TO 20mA/LED
4.7µF
PWM INPUT
0 TO 25V
R1
14.3kΩ
C3
1µF
EN1
EN2
R2
14.3kΩ SET
RSET
9.09kΩ
MAX1570
LED1
LED2
LED3
LED4
LED5
GND
PGND
Figure 2. Dimming Using Filtered-PWM Signal
1µF
1µF
C1P C1N C2P C2N
1Ω
IN
OUT
VIN
4.7µF
2.2µF
2.2µF
EN1
EN2
SET
RSET
MAX1570
LED1
LED2
LED3
LED4
LED5
GND PGND
Figure 3. C-R-C Filter Reduces Input Ripple
Chip Information
TRANSISTOR COUNT: 3187
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