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MAX5091BASA

28V, 100mA, Low-Quiescent-Current LDO with Reset and Power-Fail Input/Output

Maxim Integrated 

MAX5091

28V, 100mA, Low-Quiescent-Current LDO

with Reset and Power-Fail Input/Output

Detailed Description

Regulator

The MAX5091 high-voltage, LDO regulator operates

from +5V to +28V input voltage. The device with-

stands up to 40V transients, providing protection against

temporary overvoltage conditions like load dump. The

MAX5091 incorporates internal feedback resistors for

factory-preset voltages of either +5V (MAX5091A) or

+3.3V (MAX5091B). The regulator is capable of driving

up to 100mA of load current and features a typical current

limit of 260mA. The regulator uses a pnp pass element

and provides low 0.5V dropout while delivering 100mA

load current. The output of the regulator follows closely to

the input during turn-on. See the Output Voltage vs. Input

Voltage graph in the Typical Operating Characteristics.

This makes the usable input voltage range for 3.3V

and 5V output down to 3.7V and 5.5V, respectively. The

MAX5091 is designed to operate with very low quiescent

current during always-on operation when not in dropout.

The regulator is stable with a wide variety of capacitors

including low-ESR ceramic 10μF (0603 case size). The

load-transient response curves depict the stability of the

LDO when using different capacitance and ESR ranges.

See the Capacitor Selection and Regulator Stability sec-

tion in the Applications Information.

Reset Output (RES)

The MAX5091 integrates a power-on-reset circuit. RES

is an open-drain output that requires a pullup resistor to

VOUT. The open-drain MOSFET can sink up to 825μA

current while keeping the RES voltage below 0.4V. The

internal reset circuit monitors the regulator output voltage

and RES asserts an active-low output when the regula-

tor output falls below a reset threshold of typically 0.9 x

VOUT. The RES output remains low when VOUT is below

the reset threshold, and remains low for the duration of

the reset timeout period (tRD). The reset timeout period is

programmable and can be set with an external capacitor

connected from CT to ground. The duration of the delay

as a function of CT is:

( ) = tRD

CCT × VCCTH + 35 × 10 −6

ICT

where VCCTH = 2.1V and ICT = 2 x 10-6 A.

The default reset timeout period is 35μs when no capaci-

tor is connected from CT to ground.

SI/SO Comparator

The MAX5091 includes an uncommitted comparator for

monitoring the input voltage or for detecting power-fail con-

ditions. The input SI is the noninverting input of the compar-

ator. The open-drain output SO asserts low when voltage

at the input SI drops below the threshold voltage, VST (see

Figure 1). The sense comparator typically has a hysteresis

of 100mV. Use the following equation to calculate the resis-

tor-divider for programming the trip voltage (VTRIP) during

power-fail. See the Typical Application Circuit.

= VTRIP

(VST × RH)

RL

+

VST

where VST = 1.16V (typ). Choose RL between 100kΩ to

300kΩ.

Enable Input

The enable (EN) is a TTL-compatible logic input. Logic

low at EN turns off the regulator and reduces the current

consumption to 17μA (typ). It is internally pulled up to a

logic-high voltage (3.6V max) by an internal resistor. Thus,

the MAX5091 is enabled by default when VS is applied

and EN is left unconnected. The regulator, reset supervi-

sor circuit, and the sense comparator can be manually

shut down by pulling EN low. For shutdown operation, the

pulldown network must be capable of sinking 3μA max,

since the internal pullup resistor sets the maximum pullup

current at 3μA. The external pulldown device should not

leak more than 1μA current when it is in the off-state.

Current Limit

The MAX5091 features a current limiter that monitors the

output current and controls the pass transistor’s gate voltage,

limiting the output current to typically 260mA. The output can

be continuously shorted to ground without damaging the

device at VS ≤ 16V. Note that the output short-circuit current

may increase the power dissipation significantly and raise the

junction temperature to its thermal-shutdown threshold. In

such a case, the MAX5091 is temporarily turned off.

Thermal Shutdown

When the junction temperature exceeds TJ = +165°C (typ),

an internal thermal sensor signals the shutdown logic to

turn off the pass transistor and allow the IC to cool. The

thermal sensor turns the pass transistor on again after the

IC’s junction temperature cools by +20°C (typ), resulting in

a cycled output during continuous thermal-overload condi-

tions. Thermal shutdown protects the MAX5091 in the event

of fault conditions. For continuous operation, do not exceed

the absolute maximum junction temperature of TJ = +150°C.

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