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Data Sheet

AD9545

Rev. A | Page 123 of 157

TEMPERATURE SENSOR

THRESHOLD

DETECTOR

INTERNAL TEMPERATURE

TEMPERATURE

WARNING

TO SYSTEM CLOCK

COMPENSATION

TO DPLL0 DELAY

COMPENSATION

TO DPLL1 DELAY

COMPENSATION

IRQ MAP

TEMPERATURE

SENSOR

TEXT

EXTERNAL TEMPERATURE

TEMPERATURE

ALARM

= BIT(S) IN THE REGISTER MAP

HIGH

TEMPERATURE

THRESHOLD

LOW

TEMPERATURE

THRESHOLD

SELECT SYSCLK

TEMPERATURE

COMPENSATION

SOURCE

SELECT DPLL0

DELAY

TEMPERATURE

COMPENSATION

SOURCE

SELECT DPLL1

DELAY

TEMPERATURE

COMPENSATION

SOURCE

Figure 95. Temperature Sensor Block Diagram

TEMPERATURE SENSOR OVERVIEW

Figure 95 shows a block diagram of the temperature sensor and

supporting circuitry. Three AD9545 functional blocks are

capable of using temperature values.

•

System clock compensation

•

DPLL0 delay compensation

•

DPLL1 delay compensation

Each of these functional blocks can receive temperature values

from two sources:

•

The internal temperature sensor (default)

•

The 16-bit external temperature bit field (which follows the

temperature format shown in Figure 96)

TEMPERATURE SOURCE SELECTION

The user selects the desired temperature source for each of the

temperature compensation functional blocks via Bits[D2:D0] of

source bit controls the routing of the temperature source to the

system clock compensation block (see the Compensation Method 1

section). The select DPLLx temperature compensation source

bits (where x is 0 or 1) control the routing of the temperature

source to the DPLL0 and DPLL1 delay compensation block (see

the Delay Compensation section). For each of the temperature

compensation source bits, Bits[D2:D0], in Register 0x2092,

Logic 0 (default) selects the internal temperature sensor,

whereas Logic 1 selects the external temperature source (see the

External Temperature Source section).

INTERNAL TEMPERATURE SENSOR

The AD9545 has an internal temperature sensor with a digital

output (see Figure 95). The sensor reflects the temperature of

the silicon die, which the user can read via the internal

temperature bit field in Register 0x3003 to Register 0x3004. The

temperature sensor indicates temperature as a 16-bit signed

(twos complement) number scaled by 2−7, as shown in Figure 96.

This format provides a range of ±256°C with 0.0078°C

resolution.

...

2–7

INTEGER PART

FRACTIONAL

PART

DECIMAL

POINT

16-BIT TEMPERATURE

Figure 96. Temperature Format

The sensor samples at approximately 25 MHz and performs a

212 sample average providing updates at a rate of approximately

6.1 kHz. The intent of the temperature sensor is for tracking

temperature variation rather than providing a measure of

absolute temperature.

Given internal temperature = 0x118D (4493 decimal), find the

corresponding temperature, T.

T = 4493 × 2−7

°C

= 35.1015625°C

Given internal temperature = 0xF833 (−1997 decimal),

T = −1997 × 2−7°C

= −15.6015625°C

The temperature sensor also routes to a threshold detector. The

threshold detector detects when temperature readings are

outside the range specified by the 16-bit high temperature

threshold (Register 0x2905 to Register 0x2906) and low

temperature threshold (Register 0x2903 to Register 0x2904) bit

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