(VCC = 5V, TA = +25°C, unless otherwise noted.)

Detailed Description

The MAX7377 is a dual-speed clock generator for micro-

controllers (μCs) and UARTs in 3V, 3.3V, and 5V applica-

tions (Figure 1). The MAX7377 is a replacement for two

crystal oscillator modules, crystals, or ceramic resonators.

The high-speed clock frequency is factory trimmed to

specific values. A variety of popular standard frequencies

are available. The low-speed clock frequency is fixed

at 32.768kHz (Table 1). No external components are

required for setting or adjusting the frequency.

Supply Voltage

The MAX7377 has been designed for use in systems with

nominal supply voltages of 3V, 3.3V, or 5V and is speci-

fied for operation with supply voltages in the 2.7V to 5.5V

range. See the Absolute Maximum Ratings section for

limit values of power-supply and pin voltages.

Oscillator

The clock output is a push-pull configuration and is

capable of driving a ground-connected 500Ω or a positive-

supply-connected 250Ω load to within 400mV of either

supply rail. The clock output remains stable over the full

operating voltage range and does not generate short out-

put cycles when switching between high- and low-speed

modes. A typical startup characteristic is shown in the

Typical Operating Characteristics.

Clock-Speed Select Input

The MAX7377 uses a logic input pin, SPEED, to set clock

speed. Take this pin low to select slow clock speed (nomi-

nally 32.768kHz) or high to select full clock speed. The

SPEED input can be strapped to VCC or to GND to select

fast or slow clock speed, or connected to a logic output

(such as a processor port) used to change clock speed

on the fly. If the SPEED input is connected to a processor

PIN

NAME

FUNCTION

1

CLOCK

Push-Pull Clock Output

2

GND

Ground

3

SPEED

Clock-Speed Select Input. Drive SPEED low to select the 32kHz fixed frequency. Drive SPEED high to

select factory-trimmed frequency.

4

VCC

Positive Supply Voltage. Bypass VCC to GND with a 0.1µF capacitor.

5

E.C.

Externally Connected. Must be externally connected to VCC.

20µs/div

MAX7377 toc18

LOW-SPEED TO HIGH-SPEED

TRANSITION

CLOCK

SPEED

400ns/div

MAX7377 toc19

LOW-SPEED TO HIGH-SPEED

TRANSISTION (EXPANDED SCALE)

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Analog Devices │ 5

MAX7377

Silicon Oscillator with Low-Power

Frequency Switching

Typical Operating Characteristics (continued)

Pin Description