NCP45492

www.onsemi.com

5

APPLICATIONS INFORMATION

Differential Output Amplifier

A differential output amplifier provides a scaled

representation of multiple bus voltages and currents to an

external device on the DIFF_OUT_P and DIFF_OUT_N

pins. These voltages and currents are presented sequentially

(under control of the Sequence Logic block) via the

Multiplexer. The common−mode voltage of the differential

output amplifier is established by the voltage on the

CM_REF_IN pin.

Current Shunt Monitor (one of four identical instances)

The differential voltage across an external shunt resistor

implemented by an op−amp and external resistor R1. This

current is supplied to the SH_Ox pin where it is converted

back to a ground−referenced voltage by external resistor R2.

The conversion gain from differential voltage across the

shunt resistor to that ground−referred voltage on SH_Ox

capacitor may be connected across R2 in order to provide

noise filtering if required in the application. Note that bias

current for the op−amp is taken from the “load” side of the

shunt resistor so that it is included in the load current

measurement.

Current Shunt Resistors

Figure 1 are used to define the full dynamic range of the

shunt current monitoring and are user application

(eq. 1)

resistance of R2 is found with the relationship;

(eq. 2)

maximum voltage of the SH_Ox pin shall not exceed

Bus Voltage Monitor (one of four identical instances)

An external voltage divider is used to scale the voltage on

the BS_INx pin to an appropriate full−scale range for the

differential output amplifier. Resistors R3 and R4 form a

resistor divider to define the full dynamic range of the bus

voltage monitor with;

(eq. 3)

Multiplexer Select

The multiplier selection is controlled by a single digital

input (MUX_SEL pin). The device will monitor this pin and

cycle through the different measured parameters in a fixed

sequence. The sequence will repeat cycle as shown in the

tables until either a timeout condition is detected or the

device is disabled. The MUX_SEL pin needs to be pulsed at

least once before normal MUX_SEL cycles begin. The

delay between the falling edge of the last initial MUX_SEL

pulse and the first rising edge of the normal MUX_SEL

cycle needs to be 14.75

ms > Td > 24.25 ms.

Operating Modes

There are two operating modes – stand−alone (one to four

channels) and paired operation (up to eight channels). In

paired operation, MODE_SEL is used to designate a

“Device A” and “Device B” of a pair. When paired, the

differential output amplifiers of the two devices are

expected to be “wire−or’ed” together, and the table logic

insures that only one device will actively drive

DIFF_OUT_P and DIFF_OUT_N at any given time. See

description in the Auxiliary Functions section for details.

Additionally, devices can be configured to operate with a

reduced channel count. See description in the Auxiliary

Functions section for details.

Power−up Sequence

applied (2.8 V − 3.8 V) for expected operation and current

consumption. The enable signal must be held low while the

are present, EN can then be pulled high or floated if standby

mode or limited function mode is desired. Refer to auxiliary

functions section for more information.