MP2696B datasheet(29/34 Pages) MPSIND

29 / 34 page

MP2696B

– SW CHARGER WITH I2C CONTROL, BOOST OUTPUT

MP2696B Rev. 1.0

MonolithicPower.com

4/16/2021

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

APPLICATION INFORMATION

Setting the NTC Resistor

Figure 14 shows the different temperature

thresholds (cold, cool, warm, and hot) that are

preset by the internal voltage divider reference

circuit.

NTC

VRNTC

Hot

Cold

Cool

Warm

NTC

Protection

RT2

RT1

RNTC

Figure 14: JEITA-Controlled NTC Protection

Circuit

To set the NTC window for a given NTC

thermistor, calculate RT1 and RT2 with Equation

(6) and Equation (7), respectively:

NTC _ HOT

NTC _ COLD

COLD

HOT

COLD

HOT

NTC _ COLD

NTC _ HOT

)











(6)

NTC _ HOT

NTC _ COLD

COLD

HOT

COLD

NTC _ COLD

COLD

HOT

NTC _ HOT

)

(1 V

) R

(1 V

) R







 





 



(7)

Where RNTC_HOT is the value of the NTC resistor

at the upper bound of its operating temperature

range, and RNTC_COLD is the value at the lower

bound. VHOT is the hot temperature threshold

percentage, which can be set to 34% or 36% of

VVRNTC. VCOLD is the cold temperature threshold

percentage, which can be set to 72% or 68% of

VVRNTC.

The warm and cool temperature thresholds can

be calculated with Equation (8) and Equation

(9), respectively:

NTC _ WARM

WARM

NTC _ WARM

// R





(8)

NTC _ COOL

COOL

NTC _ COOL

// R





(9)

Using the results from these calculations,

choose the closest warm and cool thresholds in

REG 08h.

If no external NTC is available, connect RT1 to

RT2 to keep the voltage on NTC within the valid

NTC window (e.g. RT1 = RT2 = 10kΩ).

Selecting the Inductor

Inductor selection requires a tradeoff between

cost, size, and efficiency. A smaller-value

inductance results a physically smaller inductor,

but also results in greater current ripple,

magnetic

hysteretic

losses,

and

output

capacitance. A higher-value inductor benefits

from lower ripple current and smaller output

filter capacitors, but results in a greater inductor

DC resistance (DCR) loss.

Table 2 shows recommended values when

selecting an inductor

Table 2: Inductor Selection Guide

RS1 (m

Ω)

Max ICC (A)

L (µH)

3.6

1.8

2.2

1.2

3.3

0.72

4.7

Choose an inductor that does not saturate

under the worst-case load condition.

Selecting the PMID Capacitor (CPMID)

Select CPMID based on the demand of the PMID

current ripple for the mode being used.

In charge mode, CPMID acts as the input

capacitor of the buck converter in charge mode.

The input current ripple can be calculated using

Equation (10):

BATT

RMS _ MAX

CC _ MAX

)





(10)

In boost mode, CPMID is the output capacitor of

the boost converter. CPMID keeps the system

voltage ripple small and ensures feedback loop

stability. The system current ripple can be

estimated with Equation (11):

BATT

SYS

BATT

RMS _ MAX

BATT

SYS

)





(11)

Select the PMID capacitors based on the ripple

current temperature rise, and ensure that the

temperature rise does not exceed 10°C. For the

best results, use ceramic capacitors with X5R

dielectrics because of their low ESR and small

temperature coefficients.

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