MAX5092(2006) 查看數據表（PDF） - Maxim Integrated

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MAX5092
(Rev.:2006)

4V to 72V Input LDOs with Boost Preregulator

Maxim Integrated 

4V to 72V Input LDOs with Boost Preregulator

Detailed Description

The MAX5092A/MAX5092B/MAX5093A/MAX5093B

include a step-up, switch-mode DC-DC converter and a

linear regulator to provide step-up/-down voltage con-

version over a wide range of input voltages. This combi-

nation of an LDO and a boost converter offers the

advantage of using a single off-the-shelf inductor in

place of the multiple-winding custom magnetics needed

in typical SEPIC or transformer-based flyback topolo-

gies. The boost preregulator is completely turned off

during normal automotive operation (VIN = 14V),

reduces quiescent current to 65µA (typ), and makes the

devices suitable for always-on power supplies.

The devices have an internal UVLO threshold of 3.8V

(max, VIN rising) that must be exceeded before the

device is enabled. When VIN is above VUVLO, the inter-

nal boost converter starts switching and regulates

VBSOUT to the programmed boost output voltage. The

low quiescent-current LDO steps down VBSOUT to the

programmed LDO output voltage. The boost output is

preset to 7V, and the LDO output is preset to 3.3V

(MAX5092A/MAX5093A) or 5V (MAX5092B/MAX5093B).

Both output voltages can be adjusted by using external

resistor-dividers.

If VIN rises above 8V (typ), the boost converter is dis-

abled, forcing VBSOUT to follow VIN. If VIN falls below

7.5V (typ), the boost converter starts switching and

regulates VBSOUT to 7V if BSFB is directly connected to

SGND. The boost converter regulates VBSOUT for VIN

down to 3.5V, providing uninterrupted operation during

low cold-crank voltages even if the programmed LDO

output voltage is greater than VIN (but less than 9V).

The boost converter turn-on response time is less than

10µs, making cold-crank input glitches transparent to

the system even at full load.

The boost-converter output is followed by a high PSRR,

low-quiescent-current LDO. The LDO rejects the

switching noise present at BSOUT and provides a

clean, regulated output voltage. The linear regulator

uses an internal p-channel MOSFET pass element.

Additional features include a power-on-reset function

with an externally adjustable timeout, an enable (EN)

input, and a hold (HOLD) regulator control input.

Boost Converter

The switch-mode converter uses a minimum off-time,

maximum on-time pulse frequency modulation (PFM)

control scheme. The internal MOSFET turns on whenev-

er VBSOUT falls below the regulation point determined

by VBSFB (see the Setting the Boost Output Voltage

(VBSOUT) section). The MOSFET turns off when the

inductor current reaches the peak current limit (2.5A

typ) or after 2.25µs maximum on-time, whichever

occurs first. The MOSFET is held off for at least 1µs

after the turn-on phase. A new switching cycle initiates

once VBSOUT falls below the threshold. In this control

scheme, switching frequency and output ripple are

functions of load current and input voltage. No frequen-

cy compensation is needed in the PFM control scheme.

The output of the boost converter is preset to 7V and is

adjustable by using external resistors. See the Setting

the Boost Output Voltage VBSOUT section. Due to the

integrated blocking diode in the MAX5092_, VBSOUT is

limited to 11V. Use the MAX5093_ for higher boost out-

put voltages (or to reduce the power dissipation in to

the package). The MAX5093_ requires an external

diode for the boost converter. Select the external diode

according to the Schottky Diode Selection (MAX5093_)

section.

Linear Regulator

The MAX5092_/MAX5093_ contain an internal p-chan-

nel MOSFET used as the pass transistor for the LDO.

The output of the boost regulator is connected to the

source of the p-MOSFET. The LDO starts up 200µs

after the boost regulator starts up. The LDO supplies

up to 250mA with a typical dropout voltage of 0.9V. The

maximum LDO output current is determined by the

package power-dissipation limit as well as the internal

current limit. The LDO is designed to be a low-quies-

cent-current type. During normal operation when the

battery voltage is > 9V, the MAX5092_/MAX5093_ con-

sume only 75µA (max) at +85°C and 100µA load.

The output voltage of the LDO is set using the SET

input. Connect SET to SGND to use the factory-preset

output voltage. Connect SET to the center of an exter-

nal resistor-divider connected from OUT to SGND to

program a different output voltage. See the Setting the

LDO Output Voltage (VOUT) section.

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