MAX1573ETE+ Maxim Integrated Products, MAX1573ETE+ Datasheet - Page 6

• Manufacturer Part Number: MAX1573ETE+
• Description: IC LED DRVR WHITE BCKLGT 16-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LEDr

Specifications of MAX1573ETE+

• Constant Current: Yes
• Topology: Linear (LDO), PWM, Step-Down (Buck), Step-Up (Boost), Switched Capacitor (Charge Pump)
• Number Of Outputs: 4
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 1MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 5V
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 28mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Efficiency: -
• Lead Free Status / Rohs Status: Details

White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
When EN1 and EN2 are grounded, the MAX1573 is in
shutdown, and the charge pump examines whether the
input voltage is greater than or less than the output volt-
age and shorts the transfer capacitor nodes to either IN
or OUT as necessary. The output is high impedance in
either case.
The MAX1573 includes a thermal-limit circuit that shuts
down the IC at about +160°C. Turn-on occurs after the
IC cools by approximately 20°C.
SET controls the LED bias current. Current flowing into
LED1, LED2, LED3, and LED4 is a multiple of the current
flowing out of SET. Set the output current as follows:
where K = 22, 66, or 219 (depending upon EN1 and
EN2, see Table 1), and R
between SET and GND (see the Typical Operating
Circuit).
Table 1. EN1/EN2 States
Figure 1. Dimming Using PWM Signal into EN1
6
True Shutdown is a trademark of Maxim Integrated Products, Inc.
EN1 = low, EN2 = low
EN1 = low, EN2 = high
EN1 = high, EN2 = low
EN1 = high, EN2 = high
EN1/EN2 STATES
_______________________________________________________________________________________
PWM INPUT
V
IN
R SET
1μF
EN2
EN1
SET
IN
I
LED
C1P C1N
1μF
_
Setting the Output Current
MAX1573
=
Shutdown
1/10 Brightness
3/10 Brightness
Full Brightness
BRIGHTNESS
K x
True Shutdown™ Mode
SET
GND
C2P C2N
1μF
⎛
⎜
⎝
is the resistor connected
R
0 6
Thermal Shutdown
.
SET
V
OUT
LED1
LED2
LED3
LED4
⎞
⎟
⎠
1μF
I
I
I
I
LED
LED
LED
LED
LED CURRENT
= 0
= 22 x I
= 66 x I
= 219 x I
SET
SET
SET
Use EN1 and EN2 inputs as a digital 2-bit number to
control on/off, 1/10, 3/10, and full current (see Table 1).
R
Output Current section).
Use EN2 for shutdown and drive EN1 with a PWM sig-
nal. Current can be varied from 1/10 to full. The wave-
forms in the Typical Operating Characteristics show the
response time of dimming. EN2 keeps the part on, elimi-
nating any soft-start delay that would impede PWM con-
trol, allowing a PWM frequency up to 50kHz (Figure 1).
Use a high-frequency PWM signal to drive an R-C-R fil-
ter on the SET pin (Figure 2). A 0% PWM duty cycle
corresponds to 18.7mA/LED, while a 100% PWM duty
cycle corresponds to 0mA/LED. At PWM frequencies
above 5kHz, C3 may be reduced.
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
a 75mA load. Alternately, increasing C
4.7µF yields input ripple of 17mV
tively, with only a small increase in footprint. The 1x
mode always has very low input ripple.
Figure 2. Dimming Using Filtered PWM Signal
SET
INPUT
PWM
0 TO
2.5V
programs the full current level (see the Setting the
Dimming Using a Filtered PWM Signal
14.3kΩ
R1
1μF
C3
V
IN
14.3kΩ
R2
9.09kΩ
Applications Information
R
Dimming Using PWM into EN1
1μF
SET
Dimming Using EN1 and EN2
EN1
EN2
SET
IN
C1P C1N
1μF
MAX1573
GND
P-P
C2P C2N
1μF
or 9mV
P-P
Input Ripple
OUT
LED1
LED2
LED3
LED4
IN
when driving
1μF
P-P
to 2.2µF or
0 TO 18.7mA/LED
, respec-