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MAX9644

nanoPower Comparators with Precision Reference in 4-Bump UCSP

Maxim Integrated 

MAX9644/MAX9645/

MAX9646

nanoPower Comparators with

Precision Reference in 4-Bump UCSP

Detailed Description

The MAX9644/MAX9645/MAX9646 are extremely small

comparators ideal for compact, low-current, and low-

voltage applications.

The ICs consume only 400nA (typ). The low-voltage

operating capability of the operating current makes these

devices extremely attractive to long-life battery-operated

devices—these applications can now use a single digital

power-supply rail to power the new generation of micro-

controllers (which can be down to 0.9V). All parts are

available in a tiny 4-bump UCSP, which is only 0.6mm tall

and occupies a 1mm x 1mm footprint and a 5-pin SOT23.

Input Stage Circuitry

Noninverting inputs are available on the MAX9644/

MAX9646 and inverting inputs are available on the

MAX9645.

The MAX9644/MAX9645/MAX9646 incorporate an inno-

vative input stage architecture that allows their input

voltage to exceed VCC by several volts (limited only by

the Absolute Maximum Ratings). This is unlike traditional

comparators that have an input ESD diode clamp between

the input and VCC, limiting this maximum overvoltage to

about 0.3V. The ICs architecture maintains a high input

impedance to input signals even when the device power-

supply voltage is completely turned off (VCC or REF

taken to 0V). This greatly benefits flexible power-saving

schemes to be easily implemented in advanced battery-

operated devices. On-chip filtering provides immunity

from any RF noise being picked up by input traces. These

devices feature an internal temperature-compensated,

low-power 0.2V reference voltage

Output Stage Structure

The MAX9644/MAX9645 have open-drain outputs that

allow them to interface to logic circuitry running from sup-

ply voltages other than the one supplied to the part. These

devices require an external pullup resistor or current

source for proper operation. Many microcontroller digital

inputs ports can be readily programmed to include these.

The MAX9646 has a push-pull output stage that can

both sink and source current, eliminating the need for an

external pullup resistor. In this case, the MAX9646 uses

the microcontroller's power supply as VCC

Applications Information

Bypassing REF/VCC

Place a 0.1μF capacitor between REF or VCC and GND

as close as possible to the device. During a switching

event, all comparators draw a current spike from their

power-supply rails. This current spike is minimized by the

use of an internal break-before-make design.

Hysteresis Operation

The ICs feature internal hysteresis for noise immunity and

glitch-free operation. If additional hysteresis is needed, an

external positive feedback network can be easily imple-

mented on the MAX9644 and MAX9646 noninverting input

devices. Additional external hysteresis is not possible on

the MAX9645 because the noninverting input of the com-

parator is not externally accessible.

Table 1. How Devices Behave Under Various Input Voltage Conditions

PART

MAX9644

MAX9645

MAX9646

INPUT VOLTAGE CONDITIONS

VIN > 0.2V

VIN < 0.2V

VIN > 0.2V

VIN < 0.2V

VIN > 0.2V

VIN < 0.2V

ACTION AT OUTPUT

External pullup resistor pulls output high.

Output asserts low.

Output asserts low.

External pullup resistor pulls output high.

Output asserts high.

Output asserts low.

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