MAX7221EWG Maxim Integrated Products, MAX7221EWG Datasheet - Page 10

• Manufacturer Part Number: MAX7221EWG
• Description: LED Drivers
• Manufacturer: Maxim Integrated Products

Specifications of MAX7221EWG

• Number Of Digits: 8
• Number Of Segments: 64
• Low Level Output Current: 320 mA
• High Level Output Current: - 45 mA
• Operating Supply Voltage: 4 V to 5.5 V
• Maximum Supply Current: 330 mA
• Maximum Power Dissipation: 941 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-24 Wide
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 R
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.
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.
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
Serially Interfaced, 8-Digit LED Display Drivers
Table 9. Maximum Segment Current for
1-, 2-, or 3-Digit Displays
Table 10. Display-Test Register Format
(Address (Hex) = 0xXF)
Note: The MAX7219/MAX7221 remain in display-test mode
(all LEDs on) until the display-test register is reconfigured
for normal operation.
10
Normal
Operation
Display Test
Mode
NUMBER OF DIGITS
______________________________________________________________________________________
MODE
DISPLAYED
1
2
3
D7
X
X
D6
X
X
D5
X
X
REGISTER DATA
Display-Test Register
D4
MAXIMUM SEGMENT
X
X
No-Op Register
D3
CURRENT
X
X
(mA)
10
20
30
D2
X
X
SET
D1
X
X
resistor
D0
0
1
fourth chip, sent the desired 16-bit word, followed by
three no-op codes (hex 0xXX0X, 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.
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.
The current per segment is approximately 100 times
the current in ISET. To select R
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 R
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. R
ingly (Table 11).
Refer to the Continuous Power Dissipation section of
the Absolute Maximum Ratings to calculate acceptable
limits for ambient temperature, segment current, and
the LED forward-voltage drop.
Applications Information
Supply Bypassing and Wiring
Selecting R
SET
Using External Drivers
must be selected accord-
SET
SET
, see Table 11. The
Resistor and
SET
= 47kΩ