MAX6953_V01 datasheet(21/23 Pages) MAXIM

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2-Wire Interfaced, 2.7V to 5.5V, 4-Digit 5 ✕ 7

Matrix LED Display Driver

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Low-Voltage Operation

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 ISEG, plus the 0.6V headroom required by

the driver output stages. The MAX6953 correctly regu-

lates ISEG with a supply voltage above this minimum

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 ✕ 7 matrix digit

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 I2C interface is constrained to

100kbps.

Computing Power Dissipation

The upper limit for power dissipation (PD) for the

MAX6953 is determined from the following equation:

PD = (V+ ✕ 15mA) + (V+ - VLED) (DUTY ✕ ISEG ✕ N)

where:

V+ = supply voltage

Duty = duty cycle set by intensity register

N = number of segments driven (worst case is 10)

VLED = LED forward voltage

ISEG = segment current set by RSET

PD = power dissipation, in mW if currents are in mA

Dissipation example:

ISEG = 40mA, N = 10, Duty = 15 / 16, VLED

= 2.4V at 40mA, V+ = 3.6V

PD = 3.6V (15mA) + (3.6V - 2.4V)

(15 / 16 ✕ 40mA ✕ 10) = 0.504W

Thus, for a 36-pin SSOP package (TJA = 1 / 0.0118 =

+85°C/W from operating ratings), the maximum allowed

ambient temperature TA is given by:

TJ(MAX) = TA + (PD ✕ TJA) = +150°C =

TA + (0.504 ✕ +85°C/W)

So TA = +107°C. Thus, the part can be operated safely

at a maximum package temperature of +85°C.

Power Supplies

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.

Board Layout

When designing a board, use the following guidelines:

1) The RSET connection to the ISET pin is a high-

impedance node, and sensitive to layout. Place

RSET right next to the ISET pin and route RSET

directly to these pins with very short tracks.

2) Ensure that the track from the ground end of RSET

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.

Chip Information

TRANSISTOR COUNT: 44,078

PROCESS: CMOS

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