Datasheet

Data Sheet ADP1046A
Rev. 0 | Page 15 of 88
CURRENT SENSE
The ADP1046A 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 14.
CS1
1kΩ 10Ω
I = 100mA
I = 10A
V
IN
OUTA
OUTB
OUTC
OUTD
ADC
12 BITS
V
REF
FAST
OCP
1:100
1V
11012-010
Figure 14. 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 ADP1046A
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 (V
OUT
− 1 V)/2 mA.
In the case of V
OUT
= 12 V, the required resistor value is 5.5 kΩ.
Typical configurations are shown in Figure 15 and Figure 16.
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.
CS2+CS2–
ADC
12 BITS
5kΩ 5kΩ
1V
I
200µA 200µA
11012-012
Figure 15. Low-Side Resistive Current Sense (Recommended)
CS2–CS2+
ADC
12 BITS
5.5kΩ 5.5kΩ
1V
I
12V
2mA 2mA
11012-011
Figure 16. High-Side Resistive Current Sense
When the CS2+ and CS2− inputs are not in use, connect them
directly to PGND, and set CS2± 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 ADP1046A also writes the 12-bit CS2
reading every 10 ms to Register 0x18.