MAX17061A Maxim Integrated Products, MAX17061A Datasheet - Page 15

• Manufacturer Part Number: MAX17061A
• Description: 8-String White LED Driver
• Manufacturer: Maxim Integrated Products

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The MAX17061A performs a diagnostic test at startup.
Open/short strings are disabled. LED fault open/short is
also detected after startup. When one or more strings
fails after startup, the corresponding current sources
are disabled. The remaining LED strings still operate
normally. When a fault is detected, bit 4 or/and bit 5, as
well as bit 0 of the fault/status resister are set (see the
Fault/Status Register section).
The MAX17061A step-up converter output voltage is
regulated according to the minimum FB_ voltages on
all the strings in use. If one or more strings are open,
the respective FB_ pins are pulled to ground. For any
FB_ lower than 175mV, the corresponding current
source is disabled. The unaffected LED strings still
operate normally. If all strings in use are open, the
MAX17061A shuts down the step-up converter.
The MAX17061A can tolerate A slight mismatch (4.4V)
between LED strings. When severe mismatches
(> 4.4V) or WLED shorts occur, the FB_ voltages will be
uneven because mismatched voltage drops across
strings. If a given FB_ voltage is higher than 5.6V (typ)
after 24µs blanking time when LEDs are turned on, an
LED short condition is detected on the respective
string. When the short continues for greater than 2ms,
the string is disabled. The controller allows the unaf-
fected LED strings to operate normally. When only one
string is in operation and there are shorts on some
LEDs, then the converter does not shut down. Instead,
the output voltage is adjusted accordingly. The LED
short-protection feature is disabled during the soft-start
phase of the step-up converter.
Figure 3. LED Current Control by DPWM Signal in Dimming
D =
I
I
0A
DPWM
LEDMAX
LED
t
DPWM
t
ON
D = 50%
t
DPWM
t
ON
Current-Source Fault Protection
______________________________________________________________________________________
Open-Current Source Protection
SMBus for LCD Panel Applications
D = 30%
8-String White LED Driver with
DPWM DIMMING MODE
The MAX17061A internally generates a DPWM signal
for accurate WLED brightness dimming control. The
DPWM frequency is adjustable through an external set-
ting resistor and has 1.5% accuracy for R
The duty cycle of this DPWM signal can be controlled
externally through two interfaces: PWM and SMBus. The
ISET pin sets the amplitude of the current sources for
each LED string (Figure 3). The internal DPWM signal
directly controls the duty cycle of these current sources.
The resulting current is chopped and synchronized to
the DPWM signal. When filtered by the slow response
time of the human eye, the overall brightness is modu-
lated in a consistent flicker-free manner.
The full-scale LED current in the DPWM dimming is
determined by resistance from the ISET pin to ground:
The acceptable resistance range is 133kΩ < R
266kΩ, which corresponds to full-scale LED current of
30mA > I
default full-scale LED current of 25mA.
The current source output is pulse-width modulated
and synchronized with a DPWM signal to reduce jitter
and flicker noise in the display.
D = 12.5%
LEDMAX
I
LEDMAX
> 15mA. Connect ISET to V
20
in DPWM Dimming Control
Full-Scale LED Brightness
mA
R
ISET
200
Dimming Control
D = 6.25%
k
FSET
= 464kΩ.
CC
ISET
for a
15
<