MAX15008ATJ+T Datasheet MAX15010ATJ+, MAX15010ATJ+T, MAX15008ATJ+T | P13-P15

Detailed Description

The MAX15008/MAX15010 integrate a 300mA LDO

voltage regulator, a voltage tracker, and an OVP con-

troller. These devices operate over a wide 5V to 40V

supply voltage range and are able to withstand load-

dump transients up to 45V.

The MAX15008/MAX15010 feature a 300mA LDO regu-

lator that consumes less than 70µA of current under

light-load conditions and feature a fixed 5V or an

adjustable output voltage (1.8V to 11V). Connect

FB_LDO to ground to select a fixed 5V output voltage

or select the LDO output voltage by connecting an

external resistive voltage-divider at FB_LDO. The regu-

lator sources at least 300mA of current and includes a

current limit of 330mA (min). Enable the LDO by pulling

EN_LDO high.

The tracker can be powered from the LDO input sup-

ply voltage or an independent voltage source. It is

designed to supply power to a remote sensor and is

able to handle the severe conditions in automotive

applications. Set the tracker output voltage by con-

necting a resistive voltage-divider to OUT_TRK and

connecting ADJ to the tracking source. The tracker

feedback, FB_TRK, and a separate tracker reference

voltage input, ADJ, offer the flexibility of setting the

tracker output to be lower, equal to, or higher than the

main (LDO) output. Pull EN_TRK to SGND to turn the

tracker off and keep the device in always-on, low-

quiescent-current operation.

The OVP controller (MAX15008 only) relies on an exter-

nal MOSFET with adequate voltage rating (V

DSS

) to

protect downstream circuitry from overvoltage tran-

sients. The OVP controller drives the gate of the exter-

nal n-channel MOSFET, and is configurable to operate

as an overvoltage protection switch or as a closed-loop

voltage limiter.

GATE Voltage (MAX15008 Only)

The MAX15008 uses a high-efficiency charge pump to

generate the GATE voltage for the external n-channel

MOSFET. Once the input voltage, V

, exceeds the

undervoltage lockout (UVLO) threshold, the internal

charge pump fully enhances the external n-channel

MOSFET. An overvoltage condition occurs when the

voltage at FB_PROT goes above the threshold voltage,

TH_PROT

. After V

TH_PROT

is exceeded, GATE is quick-

ly pulled to PGND with a 63mA pulldown current. The

MAX15008 includes an internal clamp from GATE to

SOURCE that ensures that the voltage at GATE never

exceeds one diode drop below SOURCE during gate

discharge. The voltage clamp also prevents the GATE-

to-SOURCE voltage from exceeding the absolute maxi-

mum rating for the V

of the external MOSFET in case

the source terminal is accidentally shorted to 0V.

Overvoltage Monitoring (MAX15008 Only)

The OVP controller monitors the voltage at FB_PROT

and controls an external n-channel MOSFET, isolating,

or limiting the load during an overvoltage condition.

Operation in OVP switch mode or limiter mode

depends on the connection between FB_PROT and the

external MOSFET.

Overvoltage Switch Mode

When operating in OVP switch mode, the FB_PROT

divider is connected to the drain of the external

MOSFET. The feedback path consists of the voltage-

divider tapped at FB_PROT, FB_PROT’s internal

comparator, the internal gate charge pump/gate

pulldown, and the external n-channel MOSFET (Figure

1). When the programmed overvoltage threshold is

exceeded, the internal comparator quickly pulls GATE

to ground and turns off the external MOSFET,

disconnecting the power source from the load. In this

configuration, the voltage at the source of the

MOSFET is not monitored. When the voltage at

FB_PROT decreases below the overvoltage threshold,

the MAX15008 raises the voltage at GATE, reconnecting

the load to the power source.

MAX15008/MAX15010

Automotive 300mA LDO Voltage Regulators

with Tracker Output and Overvoltage Protector

______________________________________________________________________________________ 13

FB_PROT

SGND

GATE

SOURCE

PROTECTOR

OUTPUT

MAX15008

Figure 1. Overvoltage Switch Configuration (MAX15008)

MAX15008/MAX15010

Automotive 300mA LDO Voltage Regulators

with Tracker Output and Overvoltage Protector

14 ______________________________________________________________________________________

Overvoltage-Limiter Mode

When operating in overvoltage-limiter mode, the feed-

back path consists of SOURCE, FB_PROT’s internal

comparator, the internal gate charge pump/gate pull-

down, and the external n-channel MOSFET (Figure 2).

This configuration results in the external MOSFET oper-

ating as a hysteretic voltage regulator.

During normal operation, GATE is enhanced 8.1V

above V

. The external MOSFET source voltage is

monitored through a resistive voltage-divider between

SOURCE and FB_PROT. When V

SOURCE

exceeds the

adjustable overvoltage threshold, an internal pulldown

switch discharges the gate voltage and quickly turns

the MOSFET off. Consequently, the source voltage

begins to fall. The V

SOURCE

fall time is dependent on

the MOSFET’s gate charge, the internal charge-pump

current, the output load, and any load capacitance at

SOURCE. When the voltage at FB_PROT is below the

overvoltage threshold by an amount equal to the hys-

teresis, the charge pump restarts and turns the

MOSFET back on. In this way, the OVP controller

attempts to regulate V

SOURCE

around the overvoltage

threshold. SOURCE remains high during overvoltage

transients and the MOSFET continues to conduct dur-

ing an overvoltage event. The hysteresis of the

FB_PROT comparator and the gate turn-on delay force

the external MOSFET to operate in a switched on/off

sequence during an overvoltage event.

Exercise caution when operating the MAX15008 in

voltage-limiting mode for long durations. Care must be

taken against prolonged or repeated exposure to

overvoltage events while delivering large amounts of

load current as the power dissipation in the external

MOSFET may be high under these conditions. To pre-

vent damage to the MOSFET, implement proper

heatsinking. The capacitor connected between

SOURCE and ground can also be damaged if the rip-

ple current rating for the capacitor is exceeded.

As the transient voltage decreases, the voltage at

SOURCE falls. For fast-rising transients and very large

MOSFETs, connect an additional capacitor from GATE

to PGND. This capacitor acts as a voltage-divider work-

ing against the MOSFET’s drain-to-gate capacitance. If

using a very low gate charge MOSFET, additional

capacitance from GATE to ground might be required to

reduce the switching frequency.

Control Logic

The MAX15008/MAX15010 LDO features two logic

inputs, EN_LDO and HOLD, making these devices suit-

able for automotive applications. For example, when

the ignition key signal drives EN_LDO high, the regula-

tor turns on and remains on even if EN_LDO goes low,

as long as HOLD is forced low and stays low after initial

regulator power-up. In this state, releasing HOLD turns

the regulator output (OUT_LDO) off. This feature makes

it possible to implement a self-holding circuit without

external components. Forcing EN_LDO low and HOLD

high (or unconnected) places the regulator into shut-

down mode reducing the supply current to less than

16µA. Table 1 shows the state of OUT_LDO with

respect to EN_LDO and HOLD. Leave HOLD uncon-

nected or connect directly to OUT_LDO to allow the

EN_LDO input to act as a standard on/off logic input for

the regulator.

FB_PROT

SGND

GATE

SOURCE

PROTECTOR

OUTPUT

MAX15008

Figure 2. Overvoltage Limiter (MAX15008)

Applications Information

Load Dump

Most automotive applications run off a multicell 12V

lead-acid battery with a nominal voltage that swings

between 9V and 16V, depending on load current,

charging status, temperature, and battery age, etc. The

battery voltage is distributed throughout the automobile

and is locally regulated down to voltages required by

the different system modules. Load dump occurs when

the alternator is charging the battery and the battery

becomes disconnected. Power in the alternator (behav-

ing now essentially as an inductor) flows into the dis-

tributed power system and elevates the voltage seen at

each module. The voltage spikes have rise times typi-

cally greater than 5ms and decay within several hun-

dred milliseconds but can extend out to 1s or more

depending on the characteristics of the charging sys-

tem. These transients are capable of destroying semi-

conductors on the first fault event.

The MAX15008/MAX15010 feature load-dump transient

protection up to +45V.

Setting the Output Voltage

The MAX15008/MAX15010 feature dual-mode opera-

tion: these devices operate in either a preset voltage

mode or an adjustable mode. In preset voltage mode,

internal feedback resistors set the linear regulator out-

put voltage (V

OUT_LDO

) to 5V. To select the preset 5V

output voltage, connect FB_LDO to SGND.

To select an adjustable output voltage between 1.8V

and 11V, use two external resistors connected as a

voltage-divider to FB_LDO (Figure 3). Set the output

voltage using the following equation:

OUT_LDO

= V

FB_LDO

x (R

+ R

) / R

where V

FB_LDO

= 1.235V and R

≤ 50kΩ.

MAX15008/MAX15010

Automotive 300mA LDO Voltage Regulators

with Tracker Output and Overvoltage Protector

______________________________________________________________________________________ 15

FB_LDO

SGND

OUT_LDO

MAX15008

MAX15010

Figure 3. Setting the LDO Output Voltage

Table 1. EN_LDO/

HHOOLLDD

Truth Table/State Table

OPERATION STATE EN_LDO HOLD OUT_LDO COMMENT

Initial State Low Don’t care OFF

EN_LDO is pulled to SGND through an internal pulldown. HOLD

is unconnected and is internally pulled up to OUT_LDO. The

regulator is disabled.

Turn-On State High Don’t care ON

EN_LDO is externally driven high turning regulator on. HOLD is

pulled up to OUT_LDO.

Hold Setup State High Low ON

HOLD is externally pulled low while EN_LDO remains high

(latches EN_LDO state).

Hold State Low Low ON

EN_LDO is driven low or left unconnected. HOLD remains

externally pulled low keeping the regulator on.

Off State Low

High or

unconnected

OFF

HOLD is driven high or left unconnected while EN_LDO is low.

The regulator is turned off and EN_LDO/HOLD logic returns to the

initial state.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24

MAX15008ATJ+T

Mfr. #:

Buy MAX15008ATJ+T

Manufacturer:

Maxim Integrated

Description:

LDO Voltage Regulators Automotive 300mA w/Tracker Output

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MAX15008ATJ+T

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