MAX1570ETE+ Maxim Integrated Products, MAX1570ETE+ Datasheet - Page 7

• Manufacturer Part Number: MAX1570ETE+
• Description: IC LED DRVR WHITE BCKLGT 16-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LEDr

Specifications of MAX1570ETE+

• Constant Current: Yes
• Topology: PWM, Step-Down (Buck), Step-Up (Boost), Switched Capacitor (Charge Pump)
• Number Of Outputs: 5
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 1MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 30mA
• Internal Switch(s): Yes
• Number Of Segments: 5
• Low Level Output Current: 30 mA
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Supply Current: 3.5 mA
• Maximum Power Dissipation: 1349 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Efficiency: -
• Lead Free Status / Rohs Status: Details

The MAX1570 is a complete charge-pump buck/boost
converter requiring only four small ceramic capacitors.
The MAX1570 utilizes a proprietary 1x/1.5x fractional
charge-pump topology to drive up to five white LEDs
with regulated constant current for uniform intensity.
The MAX1570 operates with a 1MHz fixed frequency.
An external resistor (R
current, while two digital inputs control on/off and pro-
vide brightness control.
The MAX1570 operates in 1x charge-pump mode until
just above dropout. Then the MAX1570 switches to 1.5x
charge-pump mode to regulate the voltage at LED1
and maintain constant LED brightness even at very low
battery voltages. Using this topology, there is no LED
brightness change during the 1x/1.5x switchover,
which guarantees no flicker on the display. The
switchover scheme has low hysteresis, minimizing
operation in the less efficient 1.5x mode. The 1x mode
produces almost no ripple, while the 1.5x mode regu-
lates the output voltage by controlling the rate at which
the transfer capacitors are charged. In this way, the
switching frequency remains constant for reduced
input ripple and stable noise spectrum.
The MAX1570 includes soft-start circuitry to limit inrush
current at turn-on. When starting up with an output volt-
age that is not near the input voltage, the output capac-
itor is charged directly from the input with a DAC
ramped current source (with no charge-pump action)
until the output voltage is near the input voltage. Once
this occurs, the charge pump determines if 1x or 1.5x
mode is required. In the case of 1x mode, the soft-start
is terminated and normal operation begins. In the case
of 1.5x mode, soft-start operates until LED1 reaches
regulation. In case of an overload condition, soft-start
repeats every 2.1ms. If the output is shorted to ground,
the output current is limited by the MAX1570 fractional-
switching technique and then the device hits thermal
shutdown once the die temperature reaches -160°C.
When EN1 and EN2 are grounded, the MAX1570 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.
White LED Current Regulator with 1x/1.5x
_______________________________________________________________________________________
SET
Detailed Description
) programs the full-scale LED
True Shutdown Mode
Output Regulation
Soft-Start
High-Efficiency Charge Pump
The MAX1570 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, LED4, and LED5 is 230 times
greater than the current flowing out of SET. Set the out-
put current as follows:
where V
and EN2, see Table 1), and R
nected between SET and GND (see the Typical
Operating Circuit).
Use EN1 and EN2 inputs as a digital 2-bit number to
control on/off, 1/3, 2/3, and full current (see Table 1).
EN1 and EN2 control the voltage at SET (V
Adjusting the SET voltage controls the current (I
through the SET resistor (R
reducing R
LED current (I
The charge-pump feedback threshold at LED1 is
increased as the current is increased to prevent
dropout in the current regulators while improving effi-
ciency at lower current settings. LED1 is regulated at
0.2V, 0.3V, or 0.4V when EN1 and EN2 are adjusted for
1/3, 2/3, or full current, respectively (see Table 1). A
higher threshold improves LED-to-LED current match-
ing, while a lower threshold improves efficiency by
allowing the 1x mode at lower input voltages.
Use EN2 for shutdown and drive EN1 with a PWM signal.
Current can be varied from 1/3 to full. The waveforms in
the Typical Operating Characteristics show the response
time of dimming. EN2 keeps the part on, eliminating any
soft-start delay that would impede PWM control, allowing
a PWM frequency up to 5kHz (Figure 1).
Use a high-frequency PWM signal to drive an R-C-R filter
on the SET pin (Figure 2). A 0% PWM duty cycle corre-
sponds to 20mA/LED, while a 100% PWM duty cycle
corresponds to 0mA/LED. At PWM frequencies above
5kHz, C3 may be reduced.
Dimming Using a Filtered-PWM Signal
SET
SET
= 0.2V, 0.4V, or 0.6V (depending upon EN1
LED_
increases I
I
LED
Applications Information
Dimming Using PWM into EN1
Dimming Using EN1 and EN2
).
_
Setting the Output Current
=
230
SET
×
SET
, which then increases the



Thermal Shutdown
R
V
SET
SET
SET
). Increasing V
is the resistor con-



SET
SET
SET
or
).
7
)