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MAX8834Y/MAX8834Z
Adaptive Step-Up Converters
with 1.5A Flash Driver
Soft-Start
The step-up converter implements a soft-start to control
inrush current when it turns on. It soft-starts by charging
C COMP with a 100μA current source. During this time,
the internal MOSFET is switching at the minimum duty
cycle. Once V COMP rises above 1V, the duty cycle
increases until the output voltage reaches the desired
regulation level. COMP is pulled to AGND with a 180 ?
(typ) internal resistor during IN, UVLO, dropout mode,
or shutdown. See the Typical Operating Characteristics
for an example of soft-start operation. Soft-start is reini-
tiated after UVLO or if the step-up converter is re-
enabled after shutdown or dropout mode.
Shutdown and Standby
The MAX8834Y/MAX8834Z are in shutdown when either
V IN or V DD are in UVLO. In shutdown, supply current is
reduced to 0.1μA (typ). When V IN is above its UVLO
threshold, but V DD is below its UVLO threshold, the IC
disables its internal reference, keeps all registers reset,
turns the step-up converter off, and turns the
FLED1/FLED2 current regulators off (high impedance).
Once a logic-level voltage is supplied to V DD , the IC
enters standby condition and is ready to accept I 2 C
commands. The internal MOSFET, synchronous rectifi-
er, and FLED1/FLED2 are also high impedance in
standby.
Typical shutdown timing characteristics are shown in
the Typical Operating Characteristics.
Parallel Connection of Current Regulators
The FLED1/FLED2 current regulators can be connected
in parallel as long as the system software properly sets
the current levels for each regulator. Unused current
regulators may be connected to ground. The FLED1/
SDA
FLED2 regulators must be disabled through I 2 C to
avoid a fault detection from an open or short.
Open/Short Detection
The MAX8834Y/MAX8834Z monitor the FLED1, FLED2,
and INDLED voltage to detect any open or short LEDs.
A short fault is detected when the voltage rises above
V OUT - 1V (typ), and an open fault is detected when
the voltage falls below 100mV. The fault detection cir-
cuitry is only activated when the corresponding current
regulator is enabled and provides a continuous moni-
tor of the current regulator condition. Once a fault is
detected, the corresponding current regulator is dis-
abled and the status is latched into the corresponding
fault register bit (see Table 15). This allows the proces-
sor to determine the MAX8834Y/MAX8834Z operating
condition.
Thermal Shutdown
Thermal shutdown limits total power dissipation in the
MAX8834Y/MAX8834Z. When the junction temperature
exceeds +160°C (typ), the IC turns off, allowing itself to
cool. The IC turns on and begins soft-start after the junc-
tion temperature cools by 20°C. This results in a pulsed
output during continuous thermal overload conditions.
I 2 C Serial Interface
An I 2 C-compatible, 2-wire serial interface controls the
step-up converter output voltage, flash, movie, and
indicator current settings, flash duration, and other
parameters. The serial bus consists of a bidirectional
serial-data line (SDA) and a serial-clock input (SCL).
The MAX8834Y/MAX8834Z are slave-only devices, rely-
ing upon a master to generate a clock signal. The mas-
ter initiates data transfer to and from the MAX8834Y/
t LOW
t SU,DAT
t HD,DAT
t SU,STA
t HD,STA
t SU,STO
t BUF
SCL
t HD,STA
t R
t HIGH
t F
START CONDITION
REPEATED START CONDITION
STOP
CONDITION
START
CONDITION
Figure 15. 2-Wire Serial Interface Timing Detail
Maxim Integrated
19
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