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 con-

sist of a temperature-compensated precision oscillator

with enable (MAX7394) or autoenable (MAX7393). The

ENABLE input on the MAX7394 manually enables or

disables 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 oper-

ation. Drive ENABLE to a logic-low to place the device in

shutdown mode. During shutdown, the oscillator is turned

off, and the CLOCK output is weakly driven high with an

ply 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 condition

of a returned clock signal. The MAX7393 is automatically

enabled whenever an active inversion function is sensed

between CLOCK and CLKIN. When no inversion 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 function,

typically provided by a microcontroller’s clock generator,

to provide an inverted version of the CLOCK output sig-

nal. The MAX7393 interprets high/low voltage or a con-

stant 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 1kΩ load or

a positive supply connected 500Ω load to within 300mV

of either supply rail. There are no impedancematching

issues when using the MAX7393/MAX7394 CLOCK out-

put. 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 microproces-

sor (μP) or microcontroller (μC) clock input. There are no

impedance-matching issues when using the MAX7393/

MAX7394. Operate the MAX7393/MAX7394 and micro-

(see the Power-Supply Considerations section for more

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

input compatibility with external clock signals.

The MAX7393/MAX7394 require no biasing components

or load capacitance. When using the MAX7393/MAX7394

to retrofit a crystal oscillator, remove all biasing compo-

nents from the oscillator input.

Power-Supply Considerations

The MAX7393/MAX7394 operate with power-supply volt-

to the same supply voltage level as the device receiving

the clock. Proper power-supply decoupling is required to

maintain the power-supply rejection performance of the

MAX7393/MAX7394. Connect 0.1μF surface-mount ceram-

if the MAX7393/MAX7394 are to operate with a large

at least 1000 times that of the output load capacitance.

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

MAX7393

CLOCK

CLKIN

ON/OFF

MAX7393/MAX7394

Precision Silicon Oscillators with

Enable or Autoenable

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