MAX7219CNG 데이터 시트보기 (PDF) - Maxim Integrated

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MAX7219CNG

Serially Interfaced, 8-Digit LED Display Drivers

Maxim Integrated 

Serially Interfaced, 8-Digit LED Display Drivers

If the scan-limit register is set for three digits or less,

individual digit drivers will dissipate excessive amounts

of power. Consequently, the value of the RSET resistor

must be adjusted according to the number of digits dis-

played, to limit individual digit driver power dissipation.

Table 9 lists the number of digits displayed and the

corresponding maximum recommended segment cur-

rent when the digit drivers are used.

Display-Test Register

The display-test register operates in two modes: normal

and display test. Display-test mode turns all LEDs on

by overriding, but not altering, all controls and digit reg-

isters (including the shutdown register). In display-test

mode, 8 digits are scanned and the duty cycle is 31/32

(15/16 for MAX7221). Table 10 lists the display-test reg-

ister format.

Table 9. Maximum Segment Current for

1-, 2-, or 3-Digit Displays

NUMBER OF DIGITS

DISPLAYED

1

2

3

MAXIMUM SEGMENT

CURRENT

(mA)

10

20

30

Table 10. Display-Test Register Format

(Address (Hex) = XF)

MODE

Normal

Operation

Display Test

Mode

REGISTER DATA

D7 D6 D5 D4 D3 D2 D1 D0

XXXXXXX0

XXXXXXX1

Note: The MAX7219/MAX7221 remain in display-test mode

(all LEDs on) until the display-test register is reconfigured

for normal operation.

No-Op Register

The no-op register is used when cascading MAX7219s

or MAX7221s. Connect all devices’ LOAD/CS inputs

together and connect DOUT to DIN on adjacent

devices. DOUT is a CMOS logic-level output that easily

drives DIN of successively cascaded parts. (Refer to

the Serial Addressing Modes section for detailed infor-

mation on serial input/output timing.) For example, if

four MAX7219s are cascaded, then to write to the

fourth chip, sent the desired 16-bit word, followed by

three no-op codes (hex XX0X, see Table 2). When

LOAD/CS goes high, data is latched in all devices. The

first three chips receive no-op commands, and the

fourth receives the intended data.

__________Applications Information

Supply Bypassing and Wiring

To minimize power-supply ripple due to the peak digit

driver currents, connect a 10µF electrolytic and a 0.1µF

ceramic capacitor between V+ and GND as close to

the device as possible. The MAX7219/MAX7221 should

be placed in close proximity to the LED display, and

connections should be kept as short as possible to

minimize the effects of wiring inductance and electro-

magnetic interference. Also, both GND pins must be

connected to ground.

Selecting RSET Resistor and

Using External Drivers

The current per segment is approximately 100 times

the current in ISET. To select RSET, see Table 11. The

MAX7219/MAX7221’s maximum recommended seg-

ment current is 40mA. For segment current levels

above these levels, external digit drivers will be need-

ed. In this application, the MAX7219/MAX7221 serve

only as controllers for other high-current drivers or tran-

sistors. Therefore, to conserve power, use RSET = 47kΩ

when using external current sources as segment dri-

vers.

The example in Figure 2 uses the MAX7219/MAX7221’s

segment drivers, a MAX394 single-pole double-throw

analog switch, and external transistors to drive 2.3”

AND2307SLC common-cathode displays. The 5.6V

zener diode has been added in series with the decimal

point LED because the decimal point LED forward volt-

age is typically 4.2V. For all other segments the LED

forward voltage is typically 8V. Since external transis-

tors are used to sink current (DIG 0 and DIG 1 are used

as logic switches), peak segment currents of 45mA are

allowed even though only two digits are displayed. In

applications where the MAX7219/MAX7221’s digit dri-

vers are used to sink current and fewer than four digits

are displayed, Table 9 specifies the maximum allow-

able segment current. RSET must be selected accord-

ingly (Table 11).

Refer to the Power Dissipation section of the Absolute

Maximum Ratings to calculate acceptable limits for

ambient temperature, segment current, and the LED

forward-voltage drop.

10 ______________________________________________________________________________________

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