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MAX8834Y

Adaptive Step-Up Converters with 1.5A Flash Driver

Maxim Integrated 

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

CCOMP with a 100µA current source. During this time,

the internal MOSFET is switching at the minimum duty

cycle. Once VCOMP rises above 1V, the duty cycle

increases until the output voltage reaches the desired

regulation level. COMP is pulled to AGND with a 180Ω

(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

VIN or VDD are in UVLO. In shutdown, supply current is

reduced to 0.1µA (typ). When VIN is above its UVLO

threshold, but VDD 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 VDD, the IC

enters standby condition and is ready to accept I2C

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/

FLED2 regulators must be disabled through I2C 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

VOUT - 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.

I2C Serial Interface

An I2C-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/

SDA

tLOW

tSU,DAT

SCL

tHD,STA

START CONDITION

tHIGH

tR

tF

tHD,DAT

Figure 15. 2-Wire Serial Interface Timing Detail

tSU,STA

tHD,STA

REPEATED START CONDITION

Maxim Integrated

tBUF

tSU,STO

STOP

START

CONDITION CONDITION

19

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