IR36021 datasheet(16/41 Pages) IRF

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IR36021

DIGITAL POL BUCK CONTROLLER with I2C AND PMBus

Interface

February 27, 2013 | Rev 3.5

REAL‐TIME MONITORING

The IR36021 can be accessed through the use of PMBus

Command codes (described on page 37) to read the real

time status of the VR system including input voltage,

output voltage, input and output current, input and output

power, efficiency, and temperature.

THEORY OF OPERATION

DEVICE POWER‐ON AND INITIALIZATION

The IR36021 is powered from a 3.3V DC supply. Figure 8

shows the timing diagram during device initialization.

An internal LDO generates a 1.8V rail to power the control

logic within the device. During initial startup, the 1.8V rail

follows the rising 3.3V supply voltage, proportional to an

internal resistor tree. The internal oscillator becomes

active at t1 as the 1.8V rail is ramping up. Until soft‐start

begins, the IR36021 PWM outputs are disabled in a high

impedance state to ensure that the system comes up in

a known state.

The controller comes out of power‐on reset (POR) at t2

when the 3.3V supply is high enough for the internal bias

central to generate 1.8V. At this time, if enabled in MTP

and when the VINSEN voltage is valid, the controller will

detect the populated phases by sensing the voltage on the

PWM pins. If the voltage is less than the Auto Phase Detect

threshold (unused PWMs are grounded), the controller

assumes the phase is unpopulated. Once the phase

detection is complete the contents of the MTP are

transferred to the registers by time t3 and the automatic

trim routines are complete by time t4. The register settings

and number of phases define the controller performance

specific to the VR configuration ‐ including trim settings,

soft start ramp rate, boot voltage and PWM signal

compatibility with the MOSFET driver.

Once the registers are loaded from MTP, the designer can

use I2C to re‐configure the registers to suit the specific VR

design requirements if desired.

TEST MODE

Driving the ENABLE and VR_HOT pins low engages a special

test mode in which the I2C address changes to 0Ah. This

allows individual in‐circuit programming of the controller.

This is specifically useful in multi‐controller systems that

use a single I2C bus. Note that MTP will not load to the

working registers until either Enable or VR_HOT goes high.

Figure 8: Controller Startup and Initialization

SUPPLY VOLTAGE

The controller is powered by the 3.3V supply rail.

Once initialization of the device is complete, steady and

stable supply voltage rails and a VR Enable signal (EN) are

required to set the controller into an active state. A high

EN signal is required to enable the PWM signals and begin

the soft start sequence after the 3.3V and VIN supply rails

are determined to be within the defined operating bands.

To maintain proper operation of the device, glitches and

narrow pulses should not be applied to EN pins.

The recommended decoupling for the 3.3V is shown in

Figure 9a. The Vcc pins should have a 0.1µF X7R type

ceramic capacitors placed as close as possible to the

package. The V18A pin must have a 4.7µF, X5R type

decoupling capacitor connected close to the package as

shown in Figure 9b.

Figure 9: (a) Vcc 3.3V decoupling, (b) V18A decoupling

It should be noted that when powering up the system the

3.3V supply for IR36021 should be up before the bias

voltage of the power stages ramp up. Likewise, when the

system is shutdown, the bias voltage of the power stages

should be disconnected before the 3.3V is ramped down

(Figure 10).

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