MCP2050-ESLASHP datasheet(15/40 Pages) MICROCHIP

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 2012-2014 Microchip Technology Inc.

DS20002299C-page 15

MCP2050

EQUATION 1-2:

Assume VBATMIN = 8V. Equation 1-2 shows 10Ω



EQUATION 1-3:

Assume ∆VRECCESSIVE = 1V and IREGMAX = 50 mA

Equation 1-3 shows 20Ω



EQUATION 1-4:

Assume ∆Slope = 15%, VBATMIN = 8V and

IREGMAX = 50 mA. Equation 1-3 shows 20Ω



1.6.3

CBAT CAPACITOR

Selecting

CBAT =10 x CREG

recommended.

However, this leads to a high-value capacitor. Lower

values for CBAT capacitor can be used with respect to

some rules. In any case, the voltage at the VBB pin

should remain above VOFF when the device is turned on.

The current peak at start-up (due to the fast charge of

the CREG and CBAT capacitors) may induce a

significant drop on the VBB pin. This drop is

proportional to the impedance of the VBAT connection

(see Figure 1-12).

The VBAT connection is mainly inductive and resistive.

Therefore, it can be modeled as a resistor (RTOT) in

series with an inductor (L). RTOT and L can be

measured.

The following formula gives an indication of the

minimum value of CBAT using RTOT and L:

EQUATION 1-5:

Equation 1-5 allows lower CBAT/CREG values than the

10x ratio we recommend.

Assume that we have a good quality VBAT connection

with RTOT =0.1

 and L = 0.1 mH.

Solving the equation gives CBAT/CREG =1.

If we increase RTOT up to 1

 the result becomes

CBAT/CREG = 1.4. However, if the connection is highly

resistive or highly inductive (poor connection), the

CBAT/CREG ratio greatly increases.

Figure 1-11 shows the minimum recommended

CBAT/CREG ratio as a function of the impedance of the

VBAT connection.

FIGURE 1-11:

MINIMUM

RECOMMENDED

CBAT/CREG RATIO

250 mA is the peak current at power-on when

VBB =5.5V

BATmin

5.5V

–

250mA

-------------------------------------



5.5V

OFF

1.0V

RECESSIVE



REGMAX

----------------------------------



Where:

VRECESSIVE = Maximum variation tolerated on

the recessive level

Slope



BA TMIN

–





REGMAX

-----------------------------------------------------------------



Where:

Slope = Maximum variation tolerated on the

slope level

IREGMAX = Maximum current the current will

provide to the load

VBATMIN >VOFF +1.0V

TABLE 1-5:

CBAT/CREG RATIO BY VBAT

CONNECTION TYPE

Connection

Type

RTOT

CBAT/CREG

Ratio

Good

0.1

 0.1 mH

Typical



0.1 mH

1.4

Highly inductive

0.1



1mH

Highly resistive



0.1 mH

BAT

REG

--------------

100L

TOT

100

-------------

------------------------------------

Where:

L = Inductor (measured in mH)

RTOT =RLINE +RTP (measured in

)

0.1

VBAT Line Inductance [mH]

CBAT/CREG Ratio as Function of the VBAT Line

Impedance

RBAT = 10

RBAT = 4

RBAT = 2

RBAT = 1

RBAT = 0.3

RBAT = 0.1

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