MAX17061AEVKIT+ Maxim Integrated Products, MAX17061AEVKIT+ Datasheet - Page 14

• Manufacturer Part Number: MAX17061AEVKIT+
• Description: Power Management Modules & Development Tools MAX17061A EVAL KIT MAX17061A EVAL KIT
• Manufacturer: Maxim Integrated Products

Specifications of MAX17061AEVKIT+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX17061A implements an IN UVLO function to
safeguard the operation in the specified range. When
IN pin voltage drops below its UVLO threshold (6.98V
typ), the converter is shut off and the BL_Stat bit of the
fault/status register is cleared. The BL_CTL bit of con-
trol register is not altered. When IN pin voltage rises
above the UVLO rising edge threshold (7.2V typ) the
backlight resumes automatically if the BL_CTL bit is set
to 1.
At startup, the MAX17061A checks the OV pin to see if
the Schottky diode is open. If the OV voltage is lower
than 84mV (typ), the boost converter does not start.
After the OV test is done, the MAX17061A performs a
diagnostic test of the LED array. The test is divided to
two phases; each phase takes approximately 1.024ms.
In the first test phase, all FB_ inputs are quickly dis-
charged down to 5.6V (typ) and then continuously dis-
charged by 800µA (typ) current sources. If a given FB_
voltage remains higher than 5.6V (typ), the string is
considered to be shorted. Otherwise, if a given FB_
voltage is higher than 3V (typ), the string is considered
to be unused. Unused strings should be tied to V
the second phase, each FB_ is precharged by an inter-
nal 400µA (typ) current source. If a given FB_ voltage
remains lower than 1V (typ), the FB_ is considered to
be a short to GND and the device is disabled. After the
LED string diagnostic phases are finished, the boost
converter starts. The total startup time is less than
10ms, including 4.2ms (typ) soft-start.
The MAX17061A can be placed into shutdown by
clearing bit 0 of the device control register (0x01).
When a critical failure is detected, the IC also enters
shutdown mode. In shutdown mode, all functions of the
IC are turned off. The fault/status register is set accor-
dingly in shutdown. When bit 0 of the device control
register (0x01) is recycled to 1, the MAX17061A exits
shutdown mode and starts. The fault/status register is
reset at startup.
A tri-level OSC input sets the internal oscillator frequen-
cy for step-up converter, as shown in Table 1. High-
frequency (1MHz) operation optimizes the regulator for
the smallest component size, at the expense of efficien-
cy due to increased switching losses. Low-frequency
(500kHz) operation offers the best overall efficiency but
requires larger components and PCB area.
8-String White LED Driver with
SMBus for LCD Panel Applications
14
______________________________________________________________________________________
Frequency Selection
Shutdown
IN UVLO
Startup
CC
. In
To protect the step-up converter when the load is open,
or the output voltage becomes excessive for any rea-
son, the MAX17061A features a dedicated overvoltage
feedback input (OV). The OV pin is tied to the center
tap of a resistive voltage-divider from the high-voltage
output. When the OV pin voltage, V
1.236V, a comparator turns off the internal power MOS-
FET. This step-up converter switch is reenabled after
the V
tion threshold. This overvoltage-protection feature
ensures the step-up converter fail-safe operation when
the LED strings are disconnected from the output.
Maintaining uniform LED brightness and dimming capa-
bility are critical for LCD backlight applications. The
MAX17061A is equipped with a bank of eight matched
current sources. These specialized current sources are
accurate to within ±1.5% between strings and can be
switched on and off within 15µs, enabling PWM fre-
quencies of up to 2kHz. All LED full-scale currents are
identical and are set through the ISET pin (15mA < I
< 30mA). When ISET is connected to V
scale current is set at the 25mA default value.
The minimum voltage drop across each current source
is approximately 625mV when the LED current is 25mA.
The low-voltage drop helps reduce dissipation while
maintaining sufficient compliance to control the LED
current within the required tolerances.
The LED current sources can be disabled by tying the
respective FB_ pin to V
powered up, the controller scans settings for all FB_
pins. If a FB_ pin is not tied to V
pulls this pin low, and the controller enables the corre-
sponding current source to regulate the string current.
If the FB_ pin is tied to V
corresponding current regulator. The current regulator
cannot be disabled by connecting the respective FB_
pin to V
All FB_ pins in use are combined to extract a lowest
FB_ voltage (LVC) (see Figure 2). LVC is fed into the
step-up converter’s error amplifier and is used to set
the output voltage.
Table 1. Frequency Selection
OSC PIN CONNECTION
OV
CC
drops 60mV (typ) hysteresis below the protec-
Open
GND
V
after the IC is powered up.
CC
CC
CC
Overvoltage Protection
SWITCHING FREQUENCY (kHz)
, the controller disables the
at startup. When the IC is
LED Current Sources
CC
, an internal circuit
1000
500
750
CC
OV
, the LED full-
, exceeds
LED