IR36021 datasheet(17/41 Pages) IRF

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IR36021

DIGITAL POL BUCK CONTROLLER with I2C AND PMBus

Interface

February 27, 2013 | Rev 3.5

Figure 10: Correct sequencing of bias voltages

The IR36021 is designed to accommodate a wide variety

of input power supplies and applications and offers

programmability of the VINSEN turn‐on/off voltages.

TABLE 1: VINSEN TURN‐ON/OFF VOLTAGE RANGE

Threshold

Range

Turn‐on

4.5V to 15.9375V in 1/16V steps

Turn‐off

4.5V to 15.9375V in 1/16V steps

1 Must not be programmed below 4.5V

The supply voltage on the VINSEN pin is compared against

a programmable threshold. Once the rising VINSEN voltage

crosses the turn‐on threshold, EN is asserted and all PWM

outputs become active. The VINSEN supply voltage is valid

until it declines below its programmed turn‐off level.

A 14:1 or 22:1 attenuation network is connected to the

VINSEN pin as shown in Figure 11. Recommended values

for a 12V system are RVIN_1 = 13kΩ and RVIN_2 = 1kΩ, with

a 1% tolerance or better. Recommended values for a

mobile 7V‐19V system are RVIN_1 = 21kΩ and RVIN_2 = 1kΩ.

CVINSEN is required to have up to a maximum value of 10nF

and a minimum 1nF for noise suppression.

Figure 11: VINSEN resistor divider network

POWER‐ON SEQUENCING

The VR power‐on sequence is initiated when all of the

following conditions are satisfied:

 IR36021 Vcc (+3.3V rail) > VCC UVLO

 Input Voltage (VINSEN rail) > Vin UVLO

 ENABLE is HIGH

 VR has no Over‐current, Over‐voltage or

Under‐voltage faults on either rail depending on

the settings

 MTP transfer to configuration registers occurred

without parity error

When the power‐on sequence is initiated, and with VBoot

set to > 0V, both rails will ramp to their configured boot

voltages

and

assert

PGood1

and

PGood2.

The slew rate to VBoot is programmed per Table 2. This

table shows that the slew‐rate of VBoot is either ½ or ¼ of

the fast rate shown in the first two columns. There is a

1/10 multiplier, which if chosen will reduce the fast rate by

a factor of 10. This multiplier can be chosen by setting the

highest bit of the register# 31Hex (refer to IR36021

On the other hand, when the power‐on sequence is

initiated, If Vboot= 0V, the VR will stay at 0V and will not

soft‐start until an operation command (margin high/low) is

received from the PMBUs or the manual_VID registers are

loaded by a non‐zero value through I2C (for example

through GUI). Note that the slew‐rate of Vout when

margining or manual_VID registers are used is equal to the

fast rate shown in Table 2.

If a margining command is executed before EN goes high,

the device will startup and rise to VBoot and then go to the

margin voltage.

When EN1 and EN2 are both active, each loop starts when

its own Enable goes high provided that other startup

conditions are met as mentioned before. Under this

condition, usually both loops start together when Vin

voltage is applied.

The two loops can be configured to share a single Enable

signal (EN1). Under this condition EN2 is configured to be

‘Don’t Care’. This mode of operation is useful when

sequencing is required. For example, one of the loops can

be configured to follow the other loop with a delay at

startup (Figure 12) or both loops can be configured to start

simultaneously with a programmable delay from EN1 going

high (Figure 13). The different options for delay are

summarized in Table 3.

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