ADP1052ACPZ-R7 datasheet(34/113 Pages) AD

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ADP1052

Data Sheet

Rev. B | Page 34 of 113

DUTY CYCLE READING

The READ_DUTY_CYCLE command (Register 0x94, which gives

the duty cycle of the PWM output value) is updated every 10 ms.

type topologies; these bits select the PWM channel (OUTA to

OUTD) for which the duty cycle value is reported. When phase-

shifted full bridge topology is used, Register 0xFE58[1] must be set

to 1. The duty cycle value is calculated based on the overlapping

of the timing of OUTA and OUTD.

SWITCHING FREQUENCY READING

The READ_FREQUENCY command (Register 0x95) is used to

report the switching frequency information in kHz.

TEMPERATURE READING

The RTD pin (Pin 23) is set up for use with an external negative

temperature coefficient (NTC) thermistor. The RTD pin has an

internal programmable current source. An ADC monitors the

voltage on the RTD pin. The RTD ADC has an input range of

1.6 V. The raw data is stored in Register 0xFEAB. It is a 12-bit

reading, which means that the LSB size is 1.6 V/4096 =

390.625 μV.

Using Register 0xFE2D[7:6], an internal precision current source

can be configured to generate a 10 μA, 20 μA, 30 μA, or 40 μA

current. This current source can be trimmed by means of an

internal DAC to compensate for thermistor accuracy. To set the

current source to the factory default value of 46 μA, write 0xE6

to Register 0xFE2D.

The output of the RTD ADC is linearly proportional to the voltage

on the RTD pin; however, thermistors exhibit a nonlinear function

of resistance vs. temperature. Therefore, it is necessary to perform

postprocessing on the RTD ADC reading to read the temperature

accurately.

By connecting an external resistor in parallel with the NTC ther-

mistor, linearization is achieved. Figure 36 shows the RTD and

OTP operation. Using the factory default value of 46 μA and

the linearization scheme, the temperature, expressed in degrees

Celsius (°C), can be read directly via the READ_TEMPERATURE

command (Register 0x8D). The temperature reading is derived

from the RTD ADC output at an update rate of every 10 ms;

however, by using Register 0xFE65[2:0], the update rate can be

changed to 63 ms, 126 ms, 252 ms, or 504 ms. The ADP1052

implements a linearization scheme based on a preselected combi-

nation of external components and current selection (see the

Temperature Linearization Scheme section).

Optionally, the user can process the RTD reading and perform

postprocessing in the form of a lookup table or polynomial

equation to match the specific NTC thermistor used.

In this case, the external resistor in parallel is not needed. With an

internal current source of 46 μA, the equation to calculate the

ADC code at a certain NTC value (RX) is given by the following

formula:

ADC CODE = 46 μA × Rx/390.7 μV

For example, at 60°C, the NTC thermistor connected to the

RTD pin is 21.82 kΩ. Therefore,

RTD ADC CODE = 46 μA × 21.82 kΩ/390.7 μV = 2570

For the overtemperature function, the RTD threshold (in volts)

can be transferred through the OT_FAULT_LIMIT command in

Temperature Linearization Scheme section.

Alternatively, the temperature reading and overtemperature

protection function can be implemented by applying an external

analog temperature sensor, such as the STLM20. See Figure 35

for more information. Using this solution, the temperature sense

range can be as low as −40°C. To facilitate this approach, disable

the internal current by writing 0x00 to Register 0xFE2D and setting

derived by the following formula:

T = 159.65 −

CODE

ADC

where the ADC CODE is the reading in Register 0xFEAB[15:4].

The recommended values of R1 and R2 are 20 kΩ and 10 kΩ,

respectively.

RTD

ADC

RTD TEMPERATURE

VALUE REGISTER

10kΩ

10µA/20µA/30µA/40µA

REG 0xFEAB[15:4]

20kΩ

STLM20

VOUT

GND

Figure 35. Temperature Sensing by an Analog Temperature Sensor

RTD

ADC

100kΩ

NTC

OT_FAULT_LIMIT

REG 0x4F

RTD TEMPERATURE

VALUE REGISTER

OT_FAULT

RESPONSE

16.5kΩ

10µA/20µA/30µA/40µA

REG 0xFEAB[15:4]

SIGNAL

CONDITIONING

TEMPERATURE

VALUE IN

CELSIUS

READ_TEMPERATURE

REG 0x8D

OT_FAULT FLAG

REG 0x7D[7]

PGOOD

OT_FAULT_RESPONSE

REG 0x50

Figure 36. RTD and OTP Operation

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