IR36021 datasheet(27/41 Pages) IRF

27 / 41 page

IR36021

DIGITAL POL BUCK CONTROLLER with I2C AND PMBus

Interface

February 27, 2013 | Rev 3.5

In PS2 mode (Constant‐On‐Time Mode), internal circuitry

determines when the inductor current declines to zero on

a cycle by cycle basis and shuts off the low‐side MOSFET at

the appropriate time in each cycle (Figure 32). This reduces

conduction losses and also lowers the switching frequency

resulting in improved efficiency because the inductor and

low‐side MOSFET are not sinking power from the output

capacitors at light loads.

When diode‐emulation is activated if phase‐1b is active

(i.e. phase‐shedding is not active), PWM‐1b becomes tri‐

state and phase‐1a goes into constant‐on‐time mode

simultaneously.

In diode‐emulation mode, if Vout drops below a certain

threshold (le_th) due to applying a load, the operation is

switched to PWM instantly.

Industry standard tri‐state drivers typically have slow tri‐

state entry times, typically which allows negative current

to build up reducing efficiency and causing ringing.

The off_time_adjust variable allows the designer to

compensate for the tri‐state delay by reducing the low‐side

FET on‐time by an equivalent amount.

Figure 32: PS2 Active Diode Emulation Mode

FAULTS & PROTECTION

The comprehensive fault coverage of the IR36021 protects

the VR against a variety of fault conditions. Faults are user

configurable through the GUI which also displays the fault

status. There are two types of fault monitoring registers. In

addition to real‐time fault registers, there are “sticky” fault

registers that can only be cleared with an I2C command or

3.3V power cycle. These will indicate if any fault has

occurred since the last power cycle, even if the fault has

cleared itself and the VR has resumed normal operation.

Table 12 lists the available faults.

TABLE 12: STICKY & NON‐STICKY FAULTS

Faults

Sticky

OTP, OCP, OVP, UVP,

VIN UVLO, 3.3V UVLO,

phase‐fault, slow‐OCP

Non‐Sticky

The controller has two programmable modes for

determining how the controller responds to faults on the

two loops. In combined mode, an over‐current or under‐

voltage fault on either loop will trigger the programmed

response on both loops (Figure 35). In individual mode,

a loop will respond only to its own over‐current or under‐

voltage fault independent from the other loop. Input

under‐voltage on 3.3V or VIN supplies, over‐voltage on

either loop or an over‐temperature fault on controllers

with single temperature sense will always shut down both

loops.

Output Over‐voltage Protection (OVP)

If the output voltage exceeds a user‐programmable

threshold (Table 15) above the set‐point, the IR36021

detects an output over‐voltage fault and latches on the

low‐side MOSFETS to limit the output voltage rise based

on the settings in Table 13.

TABLE 13: OVP ACTION

OVP Action

Low‐side MOSFET latched on

Low‐side MOSFET on until

Output<0.248V

Under OVP conditions, the low‐side MOSFETs can be

configured to remain latched indefinitely (Figure 33) or

remain latched on until the output voltage falls below the

threshold at which time the low‐side MOSFETs are

released (Figure 34). This release mode can reduce or

prevent undershoot of the output voltage. In the release

mode, if the output voltage rises above the OVP level the

low side MOSFET’s will again be turned on until Vout drops

below the release threshold level.

During soft‐start, OVP is triggered at the fixed soft‐start

level. This level can be chosen from three different values

of 1.275V, 1.2V or 1.35V. Optionally, the OVP may be

allowed to remain active while the IR36021 is disabled to

prevent system leakage from over‐voltaging the output

(Table 14).

VOUT1

Measured voltage representing

I_inductor_phase-1a

PWM-1a

Programmed

on-time

Calculated low-

side FET on-time

Zero-crossing prediction

at the correct time

IR36021 Datasheet(PDF) 27 Page - International Rectifier

IR36021 Datasheet(HTML) 27 Page - International Rectifier

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Datasheet Download

Link URL