MAX6953 Maxim Integrated Products, MAX6953 Datasheet - Page 21

• Manufacturer Part Number: MAX6953
• Description: 2-Wire Interfaced/ 2.7V to 5.5V/ 4-Digit 5 x 7 Matrix LED Display Driver
• Manufacturer: Maxim Integrated Products

The MAX6953 works over the 2.7V to 5.5V supply
range. The minimum useful supply voltage is deter-
mined by the forward-voltage drop of the LEDs at the
peak current I
the driver output stages. The MAX6953 correctly regu-
lates I
voltage. If the supply drops below this minimum volt-
age, the driver output stages may brown out, and be
unable to regulate the current correctly. As the supply
voltage drops further, the LED segment drive current
becomes effectively limited by the output driver's on-
resistance, and the LED drive current drops. The char-
acteristics of each individual LED in a 5
are well matched, so the result is that the display inten-
sity dims uniformly as supply voltage drops out of regu-
lation and beyond. The MAX6953 operates down to 2V
supply voltage (although most displays are very dim at
this voltage), providing that the MAX6953 is powered
up initially to at least 2.7V to trigger the device's internal
reset, and also that the I
100kbps.
The upper limit for power dissipation (PD) for the
MAX6953 is determined from the following equation:
where:
V+ = supply voltage
Duty = duty cycle set by intensity register
N = number of segments driven (worst case is 10)
V
I
P
Dissipation example:
Thus, for a 36-pin SSOP package (T
+85°C/W from operating ratings), the maximum allowed
ambient temperature T
SEG
LED
D
P
I
SEG
= power dissipation, in mW if currents are in mA
D
= segment current set by R
= (V+
= LED forward voltage
SEG
= 40mA, N = 10, Duty = 15 / 16, V
= 2.4V at 40mA, V+ = 3.6V
T
T
J(MAX)
A
2-Wire Interfaced, 2.7V to 5.5V, 4-Digit 5
with a supply voltage above this minimum
P
+ (0.504
✕
(15 / 16
D
15mA) + (V+ - V
SEG
= 3.6V (15mA) + (3.6V - 2.4V)
= T
Computing Power Dissipation
, plus the 0.6V headroom required by
______________________________________________________________________________________
✕
A
✕
40mA
+ (P
A
+85°C/W)
is given by:
2
Low-Voltage Operation
D
C interface is constrained to
✕
✕
LED
T
10) = 0.504W
JA
SET
) = +150°C =
) (DUTY
JA
✕
= 1 / 0.0118 =
LED
✕
7 matrix digit
I
SEG
✕
N)
Matrix LED Display Driver
So T
at a maximum package temperature of +85°C.
The MAX6953 operates from a single 2.7V to 5.5V
power supply. Bypass the power supply to GND with a
0.1µF capacitor as close to the device as possible. Add
a 47µF capacitor if the MAX6953 is not close to the
board's input bulk decoupling capacitor.
When designing a board, use the following guidelines:
1) The R
2) Ensure that the track from the ground end of R
TRANSISTOR COUNT: 44,078
PROCESS: CMOS
impedance node, and sensitive to layout. Place
R
directly to these pins with very short tracks.
routes directly to GND pin 19 (PDIP package) or
GND pin 17 (SSOP package), and that this track is
not used as part of any other ground connection.
A
SET
= +107°C. Thus, the part can be operated safely
right next to the ISET pin and route R
SET
connection to the ISET pin is a high-
Chip Information
Power Supplies
Board Layout
✕
SET
SET
7
21