MP2626 datasheet(30/34 Pages) MPS

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MP2626 – SINGLE CELL LI-ION SWITCHING CHARGER WITH USB OTG

MP2626 Rev. 1.0

www.MonolithicPower.com

2/28/2015

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

NTC_hot

NTC _Cold

NTC_ Cold

NTC_Hot

(TL TH)

(1 TL) TH R

(1 TH) TH R

)

××

−

−×

− −

(18)

For example, the NCP18XH103 thermistor has

the following electrical characteristic:

At 0oC, RNTC_Cold=27.445kΩ;

At 50oC, RNTC_Hot=4.1601kΩ;

Base on equation (17) and equation (18),

RT1=6.65kΩ and RT2=24.9kΩ are suitable for an

NTC window between 0oC and 50oC

If no external NTC is available, connect RT1 and

RT2 to keep the voltage on the NTC pin within the

valid NTC window: e.g., RT1=RT2=10kΩ.

Figure 13: NTC Function Block

For Convenience, an NTC thermistor design

spreadsheet is also provided, please inquire if

necessary.

Setting the Output Voltage in Boost Mode

In the boost mode, the output voltage on the VIN

pin can be regulated to the value customer

required between 4.2V and 6V by the resistor

divider at FB pin as R1 and R2 in the typical

application circuit.

R1 R2

V1.2V

=×

(19)

Where, 1.2V is the voltage reference of boost

output voltage. With a typical value for R2, 10k

Ω,

R1 can be determined by:

V1.2V

1.2V

−

=×

(20)

For example, for a 5V output voltage, R2 is 10k

Ω,

and R1 is 31.6k

Ω.

Setting the Output Current Limit in Boost

Mode

In the boost mode, connect a resistor form the

OLIM pin to AGND to program the output current

limit. The relationship between the output current

limit and setting resistor is as follows:

)

(

)

(

2800

)

(

OLIM

(21)

The output current limit of the boost can be

programmed up to 1.5A (min). Considering 15%

output current limit accuracy, typical 1.79A output

current limit is required. According to the above

equation, given 50mΩ sense resistor, 49.9kΩ

ROLIM will get 1.79A output current limit.

Selecting the Inductor

Inductor selection trades off between cost, size,

and efficiency. A lower inductance value

corresponds with smaller size, but results in

higher ripple currents, higher magnetic hysteretic

losses, and higher output capacitances. However,

a higher inductance value benefits from lower

ripple current and smaller output filter capacitors,

but results in higher inductor DC resistance (DCR)

loss.

Choose an inductor that does not saturate under

the worst-case load condition.

1. In Charge Mode

When MP2626 works in charge mode (as a Buck

Converter), estimate the required inductance as:

BATT

L_ MAX

−

=×

(22)

Where VIN, VBATT, and fSW are the typical input

voltage, the CC charge threshold, and the

switching frequency, respectively.

ΔIL_MAX is the

maximum inductor ripple current, which is usually

designed at 30% of the CC charge current.

With a typical 5V input voltage, 30% inductor

current ripple at the corner point between trickle

charge

and

charge

(VBATT=3V),

the

inductance is 2.2

μH (for a 1.2MHz switching

frequency) and 4.4

μH (for a 600kHz switching

frequency).

MP2626 Datasheet(PDF) 30 Page - Monolithic Power Systems

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