MAX1795 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX1795

Low-Supply Current, Step-Up DC-DC Converters with True Shutdown

Maxim Integrated 

MAX1795/MAX1796/

MAX1797

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

Pin Description

PIN

NAME

FUNCTION

1

LBI

Low-Battery Comparator Input. Internally set to trip at +0.85V. This function remains operational in

shutdown.

2

FB

Dual-Mode™ Feedback Input. Connect to GND for preset 5.0V output. Connect to OUT for preset 3.3V

output. Connect a resistive voltage-divider from OUT to GND to adjust the output voltage from 2V to 5.5V.

3

LBO

Low-Battery Comparator Output, Open-Drain Output. LBO is high impedance when VLBI < 0.85V.

This function remains operational in shutdown.

4

SHDN

Shutdown Input. If SHDN is high, the device is in shutdown mode, OUT is high impedance, and LBI/LBO

are still operational. Connect shutdown to GND for normal operation.

5

GND Ground

6

LX

Inductor Connection

7

OUT Power Output. OUT provides bootstrap power to the IC.

8

BATT Battery Input and Damping Switch Connection

Detailed Description

The MAX1795/MAX1796/MAX1797 compact step-up

DC-DC converters start up with voltages as low as

0.85V and operate with an input voltage down to +0.7V.

Consuming only 25μA of quiescent current, these devices

have an internal synchronous rectifier that reduces

cost by eliminating the need for an external diode and

improves overall efficiency by minimizing losses in the

circuit (see Synchronous Rectification section for details).

The internal N-channel MOSFET power switch resistance

is typically 0.17Ω, which minimizes losses. The LX switch

current limits of the MAX1795/MAX1796/MAX1797 are

0.25A, 0.5A, and 1A, respectively.

All three devices offer Maxim’s proprietary True Shutdown

circuitry, which disconnects the output from the input

in shutdown and puts the output in a high impedance

state. These devices also feature Maxim’s proprietary

LX-damping circuitry, which reduces EMI in noise-sensi-

tive applications. For additional in-system flexibility, the

LBI/LBO comparator remains active in shutdown. Figure

1 is a typical application circuit.

Control Scheme

A unique minimum-off-time, current-limited control

scheme is the key to the MAX1795/MAX1796/MAX1797s’

low operating current and high efficiency over a wide

load range. The architecture combines the high output

power and efficiency of a pulse-width-modulation (PWM)

device with the ultra-low quiescent current of a traditional

VIN

1M

SHDN

BATT

22µH

LX

VIN

LBO MAX1795 OUT COUT*

MAX1796

MAX1797 GND

LBI

FB

47µF

VOUT = 3.3V

*SEE TABLE 1 FOR COMPONENT VALUES.

Figure 1. Typical Application Circuit

pulse-skipping controller (Figure 2). Switching frequency

depends upon the load current and input voltage, and can

range up to 500kHz. Unlike conventional pulse-skipping

DC-DC converters (where ripple amplitude varies with

input voltage), ripple in these devices does not exceed the

product of the switch current limit and the filter-capacitor

equivalent series resistance (ESR).

Dual Mode is a trademark of Maxim Integrated Products.

www.maximintegrated.com

Maxim Integrated │  8

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