Detailed Description

Differences Between

MAX6950 and MAX6951

The MAX6950 is a five-digit common-cathode display

driver. It drives five digits, with each digit comprising

eight LEDs with cathodes connected to a common

cathode. The display limit is therefore 40 LEDs or digit

segments.

The MAX6951 is an eight-digit common-cathode dis-

play driver. It drives eight digits, with each digit com-

prising eight LEDs. The only difference between the

MAX6950 and MAX6951 is that the MAX6950 is missing

three digit drivers. The MAX6950 can be configured to

scan eight digits, but if the last three digits are wired

up, they do not light.

The MAX6950/MAX6951 use a unique multiplexing

scheme to minimize the connections between the driver

and LED display. The scheme requires that the seg-

ment connections are different to each of the five

(MAX6950) or eight (MAX6951) digits (Table 1). This is

shown in the Typical Application Circuit, which uses

single-digit type displays. The MAX6950/MAX6951 are

not intended to drive multidigit display types, which

have the segments internally wired together, unless the

segments are wired with the common cathodes to fol-

low Table 1. The MAX6950/MAX6951 can drive multi-

digit LED displays that have the segments individually

pinned for each digit because then the digits can be

connected together correctly externally, just as if indi-

vidual digits were used.

Serial-Addressing Modes

The microprocessor interface on the MAX6950/

MAX6951 is a SPI-compatible 3-wire serial interface

using three input pins (Figure 1). This interface is used

to write configuration and display data to the MAX6950/

MAX6951. The serial interface data word length is 16

bits, which are labeled D15–D0 (Table 2). D15–D8 con-

tain the command address, and D7–D0 contain the

data. The first bit received is D15, the most-significant

bit (MSB). The three input pins are:

•CLK is the serial clock input, and may idle low or

high at the start and end of a write sequence.

•

CS is the MAX6950/MAX6951s’ chip-select input,

and must be low to clock data into the MAX6950/

MAX6951.

•

DIN is the serial data input, and must be stable

when it is sampled on the rising edge of the clock.

Serially Interfaced, +2.7V to +5.5V,

5- and 8-Digit LED Display Drivers

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5

PIN

NAME

FUNCTION

1

DIN

Serial Data Input. Data is loaded into the internal 16–bit Shift register on CLK’s rising edge.

2

CLK

Serial-Clock Input. On CLK’s rising edge, data is shifted into the Internal Shift register. On CLK’s

falling edge, data is clocked out of DOUT. CLK input is active only while CS is low.

3–6, 10–14

DIGX, SEGX

Digit X outputs sink current from the display common cathode when acting as digit drivers.

Segment X drivers source current to the display. Segment/digit drivers are high impedance when

turned off.

8

GND

Ground

9

OSC

together set the multiplex clock frequency. When the external clock is used, OSC should be driven

by a 1MHz to 8MHz clock.

15

CS

Chip-Select Input. Serial data is loaded into the Shift register while CS is low. The last 16 bits of

serial data are latched on CS’s rising edge.

16

V+

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

PAD

Exposed pad

Exposed pad on package underside. Connect to GND.

Pin Description