# Frequently asked questions (FAQs) on the IR38060/2/3/4 and IR38163/4/5 series – KBA237068

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1.1 Set the switching frequency on an IR38060/2/3/4

IR38060/2/3/4/ and IR38163/4/5 operate in two modes: analog and digital.

1.1.1 Digital mode

In digital mode, configure the switching frequency in the one-time programmable (OTP) area. The combination of 0x32 and 0x33 registers defines the frequency. These registers can be written by loading a configuration file through the PMBus or using an I2C command.

Use the switching frequency values specified in the datasheet for best accuracy in telemetry.

1.1.2 Analog mode

In analog mode, the switching frequency is set by the resistor on the RT/SYNC pin. When setting the switching frequency with a resistor, do not parallel with another resistor. Table 1 shows how the switching frequency is changed with the resistor.

Table 1 Switching frequency

 Resistor [Ω] Freq [kHz] 499 306 1050 356 1540 400 2050 444 2610 500 3240 550 3830 600 4530 706 5230 750 6040 800 6980 923 7870 1000 8870 1091 9760 1200 10700 1333 11800 1500

Analog Imon voltage is reporting under 0.3 V

The Imon voltage for IR38060/2/3/4 parts in analog mode can drop to low levels of less than 300 mV. The datasheet's minimum value of 0.3 V is mentioned for accuracy purposes only; it does not necessarily indicate that this is the lowest value that Imon reporting can go.

The Imon voltage can be calculated from the following equation:

Where,

Output_current_reading_analog [A] = Internal current measurement

IMON [V] = IMON pin voltage

Current_max [A] = Maximum current for part

Table 2 indicates the maximum current of parts

Table 2 IR3806X parts

 Sl. no. MPN Current rating (A) 1 IR38060 10 2 IR38062 22.5 3 IR38063 37.5 4 IR38064 52.5

The range of Imon varies depending on the part selected. The datasheet guarantees the accuracy spec for
+/-1.5 A. An IMON reading of 1.1 V does not correspond to the max current specified for the product but rather the linear region of accuracy. Note that the voltage of 1.1 V would correspond to a current that exceeds the rated current for the product, and the overcurrent protection (OCP) would have tripped before the IMON voltage got to that level.

Unable to reach the corner limits of analog TMON voltage, 500 mV to 1.1 V

In analog mode, IR38060/2/3/4 parts have the analog TMON voltage range shown on the datasheet as 0.5 V to 1.1 V, which is derived from the actual design limit specifications. The design limits are much wider than the absolute operational limits of the part to provide a sufficient design margin. For a temperature range of –40°C to 125°C, expect the TMON to have corresponding voltages of ~0.607 V to 0.98 V.

The TMON voltage can be calculated from the following equation:

V(TMON)=(T-27)×22.65mV+0.759

Where,

V(TMON) = Temperature monitoring pin voltage

T = Internal temperature measurement

Default reference voltage in analog mode

Analog mode comes with a pre-defined factory configuration. A reference voltage of 0.5 V is set at the feedback pin in the factory configuration. You must match the resistor divider of the VSNS pin and FB pin to set the output voltage. Note that the parts that come with evaluation boards have a pre-defined reference voltage set at 1.2 V.

IR38060 has some units with different reference voltages from the factory for customer-specific configurations. These units have different ordering part numbers and are mentioned in the datasheet. Resolution for IR38060/2/3/4 and IR38163/4/5 are different from the resolution of the PMBus command/I2C register.

The resolution of a PMBus command/I2C register may not match the resolution ability of the IR38060/2/3/4 and IR38163/4/5 parts. Note that the IR38x6x platform does not support the VOUT_MODE command; the only format it supports is the Linear format. For Vout-related commands, the exponent is fixed at –8. In addition, note that while an exponent of –8 implies a resolution of 3.9 mV for Vout-related commands, the finest native resolution for the IR38X6X platform is 5 mV. This  means that intermediate command values are truncated to the closest lower 5 mV. VOUT_COMMAND does not apply to IR38163/4/5 parts unless the PMBUS command is used to control the output voltage.

Example:

• VOUT_COMMAND 1.1992 V equals to I2C register 0x24 0x25 values are 0x0133 (1.1992 V).
• IR38060/2/3/4/ and IR38163/4/5 rounds 1.1992 V to 1.2 V using 5-mV resolution.

References

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