MIC2132 datasheet(27/48 Pages) MICROCHIP

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DS20006654B-page 27

MIC2132

Because the current sensing range is ±120 mV, the

output voltage range of VDROOP is 0V to 0.9V.

The part of the schematic to implement the AVP for a

5V output is shown in Figure 4-16. The underlying

assumption is that the current sense is done using

sense resistors independent of temperature.

The sizing starts with the conditions: VDROOP = 0V for

IOUT = 0A and VDROOP = 600 mV for IOUT = IOUT(MAX).

Depending on the voltage drop across the sense

resistors at IOUT(MAX), the DROOP pin can have a

value

different

from

600

mV,

assuming

that

VDROOP(IOUTMAX) = 600 mV.

Step 1: Sizing the resistors for getting (1+Ɛ)

* VOUT at

IOUT = 0A. Because VDROOP = 0V, we have VOUT

according to Equation 4-21:

EQUATION 4-21:

As a first approximation, consider choosing RFBB2

small enough so that RFBB2||RDROOP ≈ RFBB2, and we

size RFBB1, RFBB2 and RFBT to get the correct 5.00V

injection and stability.

Step 2: Sizing the resistors to have the trip of

VOUT *2⋅Ɛ from IOUT = 0A to IOUT = IOUT(MAX) or from

VDROOP = 0V to VDROOP = 600 mV.

Then,

EQUATION 4-22:

If RDROOP >> RFBB2 in Equation 4-22, then we can

simplify the equation as shown in Equation 4-23 or

Equation 4-24:

EQUATION 4-23:

EQUATION 4-24:

Step 3: The RFBB1 is slightly adjusted to get

VOUT * (1 + Ɛ) for IOUT = 0A. The result is in

Figure 4-16.

FIGURE 4-16:

AVP Implementation for 5V

Output with 2% AVP Range for DROOP Pin

Range 0V to 600 mV.

Equation 4-23 and Equation 4-24 can also have the

exact solution; the main difficulty being to find standard

resistors of 0.1% to respect the initial positioning of +Ɛ

for IOUT = 0A and the 2⋅Ɛ move down for IOUT(MAX).

The example above was based on temperature-

independent current sensing using sense resistors. In

case the bottom FET is used, the VDROOP is defined as:

EQUATION 4-25:

Considering the sensing current range of 120 mV, it

results that the operating maximum voltage value is:

EQUATION 4-26:

Since RDSON(LS) increases to about 2x at +125°C

related to the value at +25°C, it is necessary to choose

RDSON *IOUT(MAX) < 60 mV at +25°C in order to

respect the sensing range over temperature.

To desensitize the AVP related to the temperature

variation of RDSON, a resistance network used with an

NTC resistor needs to be used, as shown in

Figure 4-17 on the next page.

VOUT =1 +

RFBT

RFBB1 + RFBB2||RDROOP

× VREF









VFBS

VREF

nD × VDROOP(MAX)

VREF

2Ɛ

RFBB2

RFFB2 + RDROOP

RFBT

RFBT + RFBB1 + RFBB2||RDROOP

××

Where:

nD = Number of 2-Phase Controller Devices

(nD = 1,2,3,4)

nD × VDROOP(MAX)

VREF

RFBB2

RFFB2 + RDROOP

RFBT

RFBT + RFBB1 + RFBB2

××

2Ɛ =

RFBB2 ×

VDROOP(MAX)

VREF

– 1









RDROOP =

2Ɛ

RFBT

RFBT + RFBB1 + RFBB2

MIC2132

FBS

RFBB1

DROOP

VOUT

RINJ

CINJ

RIP_INJ

GFB

RDROOP

RFBB2

RFBT

CFF

RBIAS

Where:

RDSON(LS) = Low-Side MOSFET Turn-On Resistance

VDROOP = VCSH – 1.2V = 8 × RDSON(LS) × IL

VDROOP(MAXOP) = 120 mV × 8 = 0.96V

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