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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

To use this feature, connect the logic signal used to

enable the PA, or equivalent, to the GSMB input.

Assertion of this signal does not change the current sta-

tus of the flash safety timer or the flash current values

stored in the I2C registers. Once the signal is deassert-

ed, the current regulators change back to their previ-

ously programmed values. Polarity of this signal is

controlled through bit 6 in the GSMB_CUR register

(Table 11). The default is active-high.

Finger-Burn Protection (NTC)

An NTC input is provided for the (optional) finger-burn

protection feature. To use this feature, connect a 100kΩ

NTC with B = 4550 between NTC and AGND. NTC

sources 20µA current and the voltage established by

this current and the NTC resistance is compared inter-

nally to a voltage threshold in the range of 200mV to

550mV, programmed through bits [2:0] of the NTC

Control register (see Table 10).

If the voltage on the NTC pin falls below the programmed

threshold during a flash event, the flash cycle is immedi-

ately terminated, and an indication is latched through bit 3

in the STATUS1 register (see Table 15).

To disable this function, clear bit 3 (enable bit) in the

NTC Control register.

MAXFLASH Function

During high load currents, the battery voltage momen-

tarily drops due to its internal ESR, together with the

serial impedance from the battery to the load. For

equipment requiring a minimum voltage for stable oper-

ation, the battery ESR needs to be calculated to esti-

mate the maximum battery current that maintains the

battery voltage above the critical threshold. Due to the

complicated measurement of the battery ESR, the

MAX8834Y/MAX8834Z feature the MAXFLASH function

to prevent the battery voltage from dropping below the

threshold voltage. See Figure 11 for details.

The MAX8834Y/MAX8834Z input voltage is monitored

during a FLASH/MOVIE event. If the input voltage

drops below a predefined threshold (VLB_TH), it indi-

cates that the FLASH/MOVIE event is drawing more

current than the battery can support. As a result, the

FLED1/FLED2 current regulators start decreasing their

output currents by one step. Therefore, the input cur-

rent is reduced and the input voltage starts to rise due

to the internal battery ESR. The input voltage is then

sampled again after tLB_TMR and compared to VLB_TH

plus a predefined hysteresis (VLB_HYS). If it is still

below VLB_TH + VLB_HYS, the FLED1/FLED2 current

regulators reduce their output current again to ensure

that minimum input voltage is available for the system.

If the input voltage is above VLB_TH + VLB_HYS, the cur-

rent regulator increases the output current by one step

(if it is less than the user-defined output current). To

disable the hysteresis, set LB_HYS[1:0] to 11. In this

case, after the FLED1/FLED2 current is reduced, it

stays at the current setting. Figures 12, 13, and 14

show examples of MAXFLASH function operation. See

Tables 12 and 13 for control register details.

The MAXFLASH function continues for the entire dura-

tion of the FLASH/MOVIE event to ensure that the

FLASH/MOVIE output current is always maximized for

the specific operating conditions.

Undervoltage Lockout

The MAX8834Y/MAX8834Z contain undervoltage lock-

out (UVLO) circuitry that disables the IC until VIN is

greater than 2.3V (typ). Once VIN rises above 2.3V

(typ), the UVLO circuitry does not disable the IC until

VIN falls below the UVLO threshold minus the hysteresis

voltage. The MAX8834Y/MAX8834Z also contain a VDD

UVLO circuitry that monitors the VDD voltage. When the

VDD voltage falls below 1.4V (typ), the contents of all

the logic registers are reset to their default states. The

logic registers are only reset in a VDD UVLO condition

and not an IN UVLO condition.

tLB_TMR

IOUT_MAX

IN

DOWN

VLB_TH

UP

CURRENT

REGULATOR

VLB_HYS

VLB_TH

Figure 11. Block Diagram of MAXFLASH Function

Maxim Integrated

17

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