ADP1046ACPZ-R7 datasheet(15/96 Pages) AD

15 / 96 page

Data Sheet

ADP1046

Rev. 0 | Page 15 of 96

THEORY OF OPERATION

CURRENT SENSE

The ADP1046 has two current sense inputs: CS1 and CS2±.

These inputs sense, protect, and control the primary input

current, secondary output current, and the share bus

information. They can be calibrated to reduce errors due to

external components.

CS1 Operation (CS1)

CS1 is typically used for the monitoring and protection of

the primary side current, which is commonly sensed using a

current transformer (CT). The input signal at the CS1 pin is fed

into an ADC for current monitoring. The range of the ADC is

0 V to 1.4 V. The input signal is also fed into a comparator for

pulse-by-pulse OCP protection. The typical configuration for

the CS1 current sense is shown in Figure 13.

CS1

1kΩ

10Ω

I = 100mA

I = 10A

VIN

OUTA

OUTB

OUTC

OUTD

ADC

12 BITS

VREF

FAST

OCP

1:100

Figure 13. Current Sense 1 (CS1) Operation

The CS1 ADC is used to measure the average value of the

primary current; the reading is averaged every 2.62 ms in an

asynchronous fashion to make fault decisions. The ADP1046

also writes the 12-bit CS1 reading every 10 ms to Register 0x13.

The fast OCP comparator is used to limit the instantaneous

primary current within each switching cycle and has a nominal

threshold of 1.2 V.

Various thresholds and limits can be set for CS1, as described in

the Current Sense and Current Limit Registers section.

CS2 Operation (CS2+, CS2−)

CS2+ and CS2− are differential inputs used for the monitoring

and protection of the secondary side current. The full-scale

range of the CS2 ADC is programmable to 60 mV or 120 mV.

The differential inputs are fed into an ADC through a pair of

external resistors that provide the necessary level shifting. The

device pins, CS2+ and CS2−, are internally regulated to approxi-

mately 1 V by internal current sources.

When using low-side current sensing, the current sources are

200 μA; therefore, the required resistor value is 1 V/200 μA = 5 kΩ.

When using high-side current sensing, the current sources are

2 mA; therefore, the resistor value required is (VOUT − 1 V)/2 mA.

In the case of VOUT = 12 V, the required resistor value is 5.5 kΩ.

Typical configurations are shown in Figure 14 and Figure 15.

Various thresholds and limits can be set for CS2±, such as OCP.

These thresholds and limits are described in the Current Sense

and Current Limit Registers section.

When not in use, the CS2+ and CS2− inputs should both be

connected directly to PGND, and CS2± should be set to high-

side current sense mode (Register 0x27[2] = 1).

The CS2 ADC is used to measure the CS2 current; the reading

is averaged every 2.62 ms in an asynchronous fashion. This

averaged reading is used to make fault decisions, such as the

CS2 OCP fault. The ADP1046 also writes the 12-bit CS2

reading every 10 ms to Register 0x18.

CS2–

CS2+

ADC

12 BITS

5.5kΩ

12V

2mA

Figure 14. High-Side Resistive Current Sense

CS2+

CS2–

ADC

12 BITS

5kΩ

200µA

Figure 15. Low-Side Resistive Current Sense (Recommended)

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