MAX900BCPP 데이터 시트보기 (PDF) - Maxim Integrated

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MAX900BCPP

Low-Cost / Ultra-Small / Single/Dual/Quad Single-Supply Comparators

Maxim Integrated 

High-Speed, Low-Power Voltage Comparators

Applications Information

Circuit Layout

Because of the large gain-bandwidth transfer function of

the MAX900–MAX903, special precautions must be

taken to realize their full high-speed capability. A printed

circuit board with a good, low-inductance ground plane

is mandatory. All decoupling capacitors (the small

100nF ceramic type is a good choice) should be mount-

ed as close as possible to the power-supply pins.

Separate decoupling capacitors for analog VCC and for

digital VDD are also recommended. Close attention

should be paid to the bandwidth of the decoupling and

terminating components. Short lead lengths on the

inputs and outputs are essential to avoid unwanted par-

asitic feedback around the comparators. Solder the

device directly to the printed circuit board instead of

using a socket.

Input Slew-Rate Requirements

As with all high-speed comparators, the high gain-band-

width product of the MAX900–MAX903 can create oscil-

lation problems when the input traverses the linear

region. For clean output switching without oscillation or

steps in the output waveform, the input must meet mini-

mum slew-rate requirements. Oscillation is largely a

function of board layout and of coupled source imped-

ance and stray input capacitance. Both poor layout and

large-source impedance will cause the part to oscillate

and increase the minimum slew-rate requirement. In

some applications, it may be helpful to apply some posi-

tive feedback between the output and + input. This

pushes the output through the transition region cleanly,

but applies a hysteresis in threshold seen at the input

terminals.

TTL Output and Latch Inputs

The comparator TTL-output stages are optimized for dri-

ving low-power Schottky TTL with a fan-out of four.

When the latch is connected to a logic high level, the

comparator is transparent and immediately responds to

changes at the input terminals. When the latch is con-

nected to a TTL low level, the comparator output latches

in the same state as at the instant that the latch command

is applied, and will not respond to subsequent changes

at the input. No latch is provided on the MAX901.

Power Supplies

The MAX900–MAX903 can be powered from separate

analog and digital supplies or from a single +5V supply.

The analog supply can range from +5V to +10V with

VEE grounded for single-supply operation (Figures 1A

and 1B) or from a split ±5V supply (Figure 1C). The VDD

digital supply always requires +5V.

In high-speed, mixed-signal applications where a com-

mon ground is shared, a noisy digital environment can

adversely affect the analog input signal. When set up

with separate supplies (Figure 1C), the

MAX900–MAX903 isolate analog and digital signals by

providing a separate AGND (VEE) and DGND.

+10V

+5V

VCC

VDD

OUT

GND

VEE

Typical Power-Supply Alternatives

+5V

+5V

+5V

VCC

VDD

OUT

GND

VEE

VCC

VDD

OUT

GND

VEE

-5V

Figure 1A. Separate Analog Supply,

Common Ground

Figure 1B. Single +5V Supply, Common

Ground

Figure 1C. Split ±5V Supply, Separate

Ground

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