Detailed Description

The MAX7393/MAX7394 precision silicon oscillators

replace crystals, ceramic resonators, and crystal oscilla-

tor modules in systems with a +2.4V to +3.6V operating

supply voltage range. The MAX7393/MAX7394 consist of

a temperature-compensated precision oscillator with

enable (MAX7394) or autoenable (MAX7393). The

ENABLE input on the MAX7394 manually enables or dis-

ables the oscillator. The CLKIN input on the MAX7393

monitors a returned clock signal to automatically enable

or disable the MAX7393 oscillator.

The MAX7393/MAX7394 are supplied at specific frequen-

cies, like crystals and resonators. A variety of popular

standard frequencies are available (see the Selector

Guide). Output frequency accuracy is guaranteed to be

within ±0.25% (TDFN) and ±1.3% (µDFN) (0°C to +85°C)

and ±1.0% (TDFN) and ±1.8% (µDFN) over the -40°C to

+125°C temperature range. No external components are

required to generate the specific frequency.

ENABLE (MAX7394)

The ENABLE input on the MAX7394 turns the oscillator

on and off. Drive ENABLE to a logic-high for normal

operation. Drive ENABLE to a logic-low to place the

device in shutdown mode. During shutdown, the oscilla-

tor is turned off, and the CLOCK output is weakly driven

high with an internal 10k

the total supply current reduces to less than 2µA.

Autoenable (CLKIN, MAX7393)

The MAX7393 features a CLKIN input that automatically

enables or disables the oscillator by sensing the condi-

tion of a returned clock signal. The MAX7393 is auto-

matically enabled whenever an active inversion function

is sensed between CLOCK and CLKIN. When no inver-

sion function is detected, the MAX7393 automatically

enters shutdown mode. During shutdown, the oscillator

is turned off, the CLKIN input is weakly driven to its last

state, and the CLOCK output is weakly driven to the

logic-level in CLKIN.

The CLKIN input relies on an external inversion func-

tion, typically provided by a microcontroller’s clock

generator, to provide an inverted version of the CLOCK

output signal. The MAX7393 interprets high/low voltage

or a constant high-impedance node on CLKIN as a

disable signal.

Figure 1 shows a test circuit to enable or disable the

MAX7393. One input of the NAND gate connects to the

CLOCK output of the MAX7393, and the other input is

driven with a logic level. A logic-high level enables the

oscillator and a logic-low level disables the oscillator.

See the Typical Operating Characteristics for typical

startup performance of the MAX7393.

Oscillator (CLOCK)

The CLOCK output is a push-pull, CMOS logic output

that is capable of driving a ground-connected 1k

Ω load

or a positive supply connected 500

Ω load to within

300mV of either supply rail. There are no impedance-

matching issues when using the MAX7393/MAX7394

CLOCK output. A typical startup characteristic is shown

in the Typical Operating Characteristics.

Output Jitter

The MAX7393/MAX7394s’ jitter performance is given in the

Electrical Characteristics table as a peak-to-peak value.

Applications Information

Interfacing to a Microcontroller

Clock Input

The MAX7393/MAX7394 CLOCK output is a push-pull,

CMOS logic output that directly drives any micro-

processor (µP) or microcontroller (µC) clock input. There

are no impedance-matching issues when using the

MAX7393/MAX7394. Operate the MAX7393/MAX7394

and microcontroller from the same supply voltage level of

more details). Refer to the microcontroller’s data sheet for

clock input compatibility with external clock signals.

The MAX7393/MAX7394 require no biasing compo-

nents or load capacitance. When using the MAX7393/

MAX7394 to retrofit a crystal oscillator, remove all bias-

ing components from the oscillator input.

Power-Supply Considerations

The MAX7393/MAX7394 operate with power-supply

receiving the clock. Proper power-supply decoupling is

required to maintain the power-supply rejection perfor-

mance of the MAX7393/MAX7394. Connect 0.1µF

if the MAX7393/MAX7394 are to operate with a large

at least 1000 times that of the output load capacitance.

Precision Silicon Oscillators with

Enable or Autoenable

6

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MAX7393

CLOCK

CLKIN

ON/OFF

Figure 1. Test Circuit to Enable or Disable the MAX7393 Oscillator