Register Descriptions

The MAX7500/MAX7501/MAX7502 have an internal pn-

junction-based temperature sensor whose analog out-

put is converted to digital form using a 9-bit

sigma-delta ADC. The measured temperature and tem-

perature configurations are controlled by the tempera-

Temperature Register

Read the measured temperature through the tempera-

ture register. The temperature data format is 9 bits,

two’s complement, and the register is read out in 2

bytes: an upper byte and a lower byte. Bit D15 is the

sign bit. When bit D15 is 1, the temperature reading is

negative. When bit D15 is zero, the temperature read-

ing is positive. Bits D14–D7 contain the temperature

data, with the LSB representing 0.5

°C and the MSB

representing 64

ted first. The last 7 bits of the lower byte, bits D6–D0,

are don’t cares. When reading the temperature register,

bits D6–D0 must be ignored. When the measured tem-

perature is greater than +127.5

°C, the value stored in

the temperature register is clipped to 7F8h. When the

measured temperature is below -64

°C, the value in the

temperature register is clipped to BF8h.

During the time of reading the temperature register, any

changes in temperature are ignored until the read is

completed. The temperature register is updated upon

completion of the next conversion.

Table 3 lists the temperature register definition.

Configuration Register

The 8-bit configuration register sets the fault queue, OS

polarity, shutdown control, and whether the OS output

functions in comparator or interrupt mode. When writing

to the configuration register, set bits D7, D6, and D5 to

Bits D4 and D3, the fault queue bits, determine the

number of faults necessary to trigger an OS condition.

must occur to trip the OS output. The fault queue pre-

vents OS false tripping in noisy environments.

Set bit D2, the OS polarity bit, to zero to force the OS

output active low. Set bit D2 to 1 to set the OS output

polarity to active high. OS is an open-drain output

under all conditions and requires a pullup resistor to

Set bit D1, the comparator/interrupt bit to zero to run

the over-temperature shutdown block in comparator

mode. In comparator mode, OS is asserted when the

Digital Temperature Sensors and Thermal

Watchdog with Bus Lockup Protection

8

_______________________________________________________________________________________

REGISTER NAME

ADDRESS (hex)

POR STATE (hex)

POR STATE

(BINARY)

POR STATE (

°C)

READ/

WRITE

Temperature

00

——

—

Read only

Configuration

01

00

0000 0000

—

R/W

02

4B0

0100 1011 0

75

R/W

03

500

0101 0000 0

80

R/W

UPPER BYTE

LOWER BYTE

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

Sign bit

1= Negative

0 = Positive

MSB

64

°C

32

°C16°C8°C4°C2°C1°C

LSB

0.5

°C

xx

xxx

x

x

DIGITAL OUTPUT

TEMPERATURE (

°C)

BINARY

hex

+125

0111 1101 0xxx xxxx

7D0x

+25

0001 1001 0xxx xxxx

190x

+0.5

0000 0000 1xxx xxxx

008x

0

0000 0000 0xxx xxxx

000x

-0.5

1111 1111 1xxx xxxx

FF8x

-25

1110 0110 0xxx xxxx

E70x

-55

1100 1000 0xxx xxxx

C90x

X = Don’t care.