MP2690 datasheet(33/37 Pages) MPS

33 / 37 page

MP2690

– ALL-IN-ONE, 2.5A SW CHARGER, 2.1A BOOST

MP2690 Rev.1.0

www.MonolithicPower.com

6/24/2016

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

APPLICATION INFORMATION

Setting the Charge Current in Charge

Mode

In charge mode, both the external sense resistor

(RS1) and the resistor (RISET) connect to ISET to

set the charge current (ICHG) of the MP2690 (see

the Typical Application circuit on page 2). Given

the expected ICHG and RS1 values, RISET can be

calculated with Equation (6):

CHG

ISET

1500

(A)

(k ) RS1(m )



 



(6)

For example, if ICHG = 2.5A and RS1 = 1

0mΩ,

then RISET = 60

kΩ.

Given a 10mΩ RS1, Table 6 lists the expected

RISET values for the typical charge current.

Table 6: Charging Current vs. RISET

RISET (kΩ)

Charge Current (A)

150

1.0

100

1.5

2.0

2.5

Setting the Input Current Limit in

Charge Mode

In charge mode, connect a resistor from ILIM to

AGND to program the input current limit if a

dedicated charger (CDP or DCP) is detected.

The relationship between the input current limit

and setting resistor is shown in Equation (7):

ILIM

40(k

)

(A)

)







(7)

RILIM must exceed 14.7

kΩ so that IIN_LIM is in the

range of 0A to 2.7A.

NTC Function in Charge Mode

internal

resistor

divider

sets

the

low

temperature threshold (VTL) and high temperature

threshold (VTH) at 66.6% of VSYS and 35% of VSYS,

respectively (see Figure 16). For a given NTC

thermistor, select an appropriate RT1 and RT2 to

set the NTC window with Equation (8) and

Equation (9):

NTC_Cold

SYS

NTC_Cold

R //R

66.6%

R //R





(8)

NTC_Hot

SYS

NTC_Hot

R //R

35%

R //R





(9)

Where RNTC_Hot is the value of the NTC resistor at

the upper bound of its operating temperature

range, and RNTC_Cold is its lower bound.

The two resistors RT1 and RT2 determine the

upper and lower temperature limits independently.

This flexibility allows the IC to operate with most

NTC resistors for different temperature range

requirements.

Calculate

RT1

and

RT2

with

Equation (10) and Equation (11):

NTC_Hot

NTC_Cold

NTC_Hot

(TL

TH)

TH TL (R

)











(10)

NTC_Cold

NTC_Hot

NTC_Cold

NTC_Hot

(TL TH) R

(1 TL) TH R

-(1-TH) TL R











(11)

For example, the NCP18XH103 thermistor has

the following electrical characteristics:

 At 0°C, R

NTC_Cold = 27.445kΩ

 At 50°C, R

NTC_Hot = 4.1601kΩ

Based on Equation (17) and Equation (18), an

RT1 value of

6.65kΩ and an RT2 value of 25.63kΩ

are suitable for an NTC window between 0°C and

50°C. Approximate values are RT1 = 6.65kΩ and

RT2 = 25.5kΩ.

If no external NTC is available, connect RT1 and

RT2 to keep the voltage on NTC within the valid

NTC window (e.g.: RT1 = RT2 = 10kΩ).

NTC

VNTC

Low Temp Threshold

High Temp Threshold

RNTC

RT1

RT2

VTL

VTH

Figure 16: NTC Function Block

For convenience, an NTC thermistor design

spreadsheet has also been provided.

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