MAX1299CEAE+T Datasheet MAX1298CEAE+, MAX1299CEAE+T, MAX1298CEAE+T | P13-P15

13 f

CLKs

WARMUP

44 f

CLKs

CONVERTION

CYCLES 2–12

REFERENCE

SAMPLING

3 f

CLKs

SUBTRACTION

AND WRITE TO

OUTPUT REGISTER

48 f

CLKs

CONVERTION CYCLES 1–12

13 f

CLKs

WARMUP

INPUT

ACQUISITION

INPUT

ACQUISITION

SSTRB

FCLK

4 f

CLKs

CONVERSION CYCLE 1

FIRST CONVERSION

SECOND CONVERSION

MAX1298/MAX1299

12-Bit Serial-Output Temperature Sensors

with 5-Channel ADC

______________________________________________________________________________________ 13

maximum time the device takes to acquire the signal.

Calculate this with the following equation:

ACQ

= 7 (R

+ R

) C

where R

is the source impedance of the input signal,

is the T/H input impedance (40kΩ), and C

is the

input sampling capacitance of the ADC (4pF). Source

impedances below 100kΩ have no significant effect on

MAX1298/MAX1299 AC performance.

Analog Input Protection

Internal protection diodes clamp the analog inputs to

and GND, so channels can swing within GND -

0.3V and V

+ 0.3V without damage. However, for

accurate conversions, the inputs should not extend

beyond the supply rails.

If an off-channel analog input extends beyond the

supply rails, limit the input current to 2mA.

Serial Digital Interface

The MAX1298/MAX1299 feature a serial interface that is

fully compatible with SPI, QSPI, and MICROWIRE

devices. For SPI/QSPI, ensure that the CPU serial inter-

face runs in master mode so it generates the serial

clock signal. Select a 2.5MHz clock frequency or less,

and set zero values for clock polarity (CPOL) and

phase (CPHA) in the µP control registers. Figure 4

shows detailed serial interface timing information. See

Tables 2–5 for programming information.

13 f

CLKs

WARMUP

3 f

CLKs

WRITE TO OUTPUT

INPUT

ACQUISITION

CLKs

SSTRB

FCLK

REF

ACQUISITION 1

REF

ACQUISITION 2

44 f

CLKs

CONVERSION CYCLE 1

CONVERSION CYCLES 2–12

REFERENCE SAMPLING

Figure 3b. Temperature Conversion Timing Diagram

Figure 3a. Voltage Conversion Timing Diagram

MAX1298/MAX1299

12-Bit Serial-Output Temperature Sensors

with 5-Channel ADC

14 ______________________________________________________________________________________

Input Data Format

Input data (configuration and conversion bytes) are

clocked into the MAX1298/MAX1299 at DIN on the ris-

ing edge of SCLK when CS is low. The start bit (MSB)

of an input data byte is the first logic 1 bit that arrives:

After CS falls,

after receipt of a complete configuration byte with no

conversion in progress,

after 16 bits have been clocked onto DOUT following a

conversion.

Output Data Format

Output data from the MAX1298/MAX1299 are clocked

onto DOUT on the falling edge of SCLK in the form of two

8-bit words, MSB first (Table 1). For temperature conver-

sions, the output is 12-bit binary (D10–S0) padded with 2

leading extraneous bits and two trailing zeros. For volt-

age conversions, the output is 12-bit two’s-complement

binary (D11–D0) with 1 sub-bit and two trailing zeros.

Figure 5 shows the bipolar transfer function.

Performing a Conversion

On power-up, the MAX1298/MAX1299 defaults to shut-

down mode. Start a conversion by transferring a configu-

ration byte and a conversion byte into DIN with the

control formats shown in Tables 2 and 3, respectively.

(See

Power Modes

for related discussion.)

SSTRB goes low on the falling edge of the last bit of the

conversion byte, and it returns high when the conversion

is complete. For best noise performance, SCLK should

remain low while SSTRB is low. Typical conversion times

are 2.2ms for temperature measurements and 1.1ms for

voltage measurements. The MSB of the 2 output bytes is

present at DOUT starting at the rising edge of SSTRB.

Successive SCLK falling edges shift the two 8-bit data

bytes out from an internal register. Additional (>16)

SCLK edges will result in zeros on DOUT.

SSTRB does not go into a high-impedance state when CS

goes high. Pulling CS high prevents data from being

clocked in or out, but it does not adversely affect a con-

version in progress. Figure 6 shows SSTRB timing details.

Subsequent conversions with the same reference mode

do not require a configuration byte.

Reference Selection

Select between internal and external voltage modes

through bit REF of the configuration byte. Set REF = 1

for internal reference mode and REF = 0 for external

reference mode.

CSS

CS1

CSO

CSH

DOUT

DIN

SCLK

VALIDVALID VALID

Figure 4. Detailed Serial Interface Timing

011111111111

011111111110

000000000010

000000000001

000000000000

111111111111

111111111110

111111111101

100000000010

100000000001

OUTPUT CODE

= +

REF

= -

REF

1LSB =

REF

2048

1LSB

+ -

(LSB)

Figure 5. Bipolar Transfer Function

MAX1298/MAX1299

12-Bit Serial-Output Temperature Sensors

with 5-Channel ADC

______________________________________________________________________________________ 15

Internal Reference

The MAX1298 has a 2.50V internal reference, while the

MAX1299 has a 1.20V internal reference. Both are fac-

tory trimmed for accuracy. When internal reference is

selected, REF can be used to drive an external load

with 100µA capability. Bypass REF to GND with a 0.1µF

(min) capacitance. Wake-up time is C x 2.5 x 10

s for

the MAX1298 and C x 1.2 x 10

s for the MAX1299.

External Reference

The MAX1298 can directly accept reference voltages at

REF from 0.8V to 2.5V, while the MAX1299 can directly

accept reference voltages from 0.8V to 1.2V. Bypass

REF to GND with a 0.1µF capacitor. Temperature mea-

surements always use internal reference.

Power Modes

The MAX1298 (MAX1299) typically requires supply cur-

rents of 380µA (350µA) or 310µA (280µA) when per-

forming voltage conversions at 100% duty cycle with

internal or external references, respectively. The differ-

ence reflects the power requirement of an internal refer-

ence buffer amplifier that can accommodate external

loads. Temperature conversions at 100% duty cycle

increase supply currents to 440µA (400µA) through

additional amplification, buffer, and bias circuitry that is

otherwise inactive.

Table 1. Output Data Format

Table 2. Configuration-Byte Format

D11 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 S0 0 0

BIT 7

(MSB)

BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1

BIT 0

(LSB)

Start 0 0 0 0 PM1 PM0 REF

BIT NAME DESCRIPTION

7 (MSB) Start First logic 1 after CS goes low. (See Input Data Format.)

6, 5, 4, 3 Must be 0000 to load a configuration byte.

2, 1 PM1, PM0 These 2 bits select the desired power mode (Table 4).

0 REF

A logic high enables the internal reference. A logic low disables the internal reference and

selects the external reference mode.

Table 3. Conversion-Byte Format

BIT 7

(MSB)

BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1

BIT 0

(LSB)

Start 0 1 0 SEL3 SEL2 SEL1 SEL0

BIT NAME DESCRIPTION

7 (MSB) Start First logic 1 after CS goes low. (See Input Data Format.)

6, 5, 4 Must be 010 to load a conversion byte.

3, 2, 1, 0

SEL3, SEL2,

SEL1, SEL0

These 4 bits select the input configuration (Table 5).

Figure 6. Detailed SSTRB Timing

CSH

SSTRB

CONV

SCK

CSS

CSB

SSTRB

SCLK

DOUT

PDO CLOCKED IN

SSTRB TIMING

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P20

MAX1299CEAE+T

Mfr. #:

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Manufacturer:

Maxim Integrated

Description:

Board Mount Temperature Sensors 12-Bit Serial-Output w/5Ch ADC

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