Rainbow Electronics MAX17061 - Manual (Page 14)

MAX17061
The MAX17061 includes power-on reset (POR) and
undervoltage lockout (UVLO) features. POR resets the
fault latch and sets all the SMBus registers to their POR
values. POR occurs when V
CC rises above 2.8V (typ).
The controller is disabled until V CC exceeds the UVLO
threshold of 4.25V (typ). Hysteresis on UVLO is approx-
imately 85mV.
The V CC and V DD pins should be bypassed to GND
with a minimum 1µF ceramic capacitor.
Startup
At startup, the MAX17061 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 MAX17061 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
CC . In
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.
Shutdown
The MAX17061 can be placed into shutdown by clear-
ing 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 including the 5V linear regulator. Only a
crude linear regulator remains on, providing a 4.35V
(typ) output voltage to V
CC , with 1µA current-sourcing
capability. The fault/status register is not reset in shut-
down. When bit 0 of the device control register (0x01)
is set to 1, the MAX17061 exits shutdown mode and
starts. The fault/status register is reset at startup.
8-String White LED Driver with
SMBus for LCD Panel Applications
14 ______________________________________________________________________________________
FB1
FSET
PGND2
PGND1
IN
V IN
2.8V TO 5.5V
EXTERNAL
5V SUPPLY
LX2
OV
FB2
FB3
FB4
FB5
FB6
FB7
FB8
L1
2.2 μH
0.1 μF
1 μF
1 μF
4.7 μF
D1
V DD
OSC
GND
V CC
PWMI PWM
ISET
V CC
LX1
MAX17061
V OUT
UP TO 45V
220pF
464k Ω
0.022 μF
5.1k Ω
CCV
SCL CLK
SDA DATA
PWMO
EP
R2
61.9k
Ω
2 μF
R1
2.21M Ω
Figure 3. Low-Input-Voltage Application Circuit