MAX7221EWG Maxim Integrated Products, MAX7221EWG Datasheet - Page 11

• 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

Table 11. R
LED Forward Voltage
The upper limit for power dissipation (PD) for the
MAX7219/MAX7221 is determined from the following
equation:
where:
Dissipation example:
Thus, for a CERDIP package (θ
Table 12), the maximum allowed ambient temperature
T
where T
The T
example above are +66.7°C and +55.6°C, respectively.
A
I
SEG
PD = (V+ x 8mA) + (V+ - V
V+ = supply voltage
DUTY = duty cycle set by intensity register
N = number of segments driven (worst case is 8)
V
I
I
40mA, V+ = 5.25V
PD = (5.25V x 8mA) + (5.25V - 1.8V)(31/32 x
40mA x 8) = 1.11W
Serially Interfaced, 8-Digit LED Display Drivers
T
150°C = T
is given by:
SEG
SEG
LED
J(MAX)
40
30
20
10
A
(mA)
limits for PDIP and SO packages in the dissipation
A
= segment current set by R
= 40mA, N = 8, DUTY = 31/32, V
= LED forward voltage
= +61.2°C.
= T
A
A
SET
+1.11W x 80°C/W
12.2
17.8
29.8
66.7
1.5
+ PD x θ
Computing Power Dissipation
______________________________________________________________________________________
vs. Segment Current and
11.8
17.1
28.0
63.7
2.0
JA
LED
V
LED
)(DUTY x I
11.0
15.8
25.9
59.3
2.5
JA
SET
(V)
= +80°C/W from
LED
10.6
15.0
24.5
55.4
3.0
SEG
= 1.8V at
x N)
9.69
14.0
22.6
51.2
3.5
The example in Figure 3 drives 16 digits using a 3-wire
µP interface. If the number of digits is not a multiple of
8, set both drivers’ scan limits registers to the same
number so one display will not appear brighter than the
other. For example, if 12 digits are need, use 6 digits
per display with both scan-limit registers set for 6 digits
so that both displays have a 1/6 duty cycle per digit. If
11 digits are needed, set both scan-limit registers for 6
digits and leave one digit driver unconnected. If one
display for 6 digits and the other for 5 digits, the sec-
ond display will appear brighter because its duty cycle
per digit will be 1/5 while the first display’s will be 1/6.
Refer to the No-Op Register section for additional infor-
mation.
Table 12. Package Thermal Resistance
Data
24 Narrow DIP
24 Wide SO
24 CERDIP
Maximum Junction Temperature (T
Maximum Ambient Temperature (T
PACKAGE
THERMAL RESISTANCE
Cascading Drivers
A
J
) = +150°C
) = +85°C
+75°C/W
+85°C/W
+80°C/W
(θ θ
JA
)
11