MP2633 – 1.5A SINGLE CELL SWITCH MODE BATTERY CHARGER

MP2633 Rev. 1.05

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29

4/19/2013

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voltage, the CC charge threshold, and the

switching frequency, respectively.

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

inductance is 1.85μH (for a 1.2MHz switching

frequency), and 3.7µH (for a 600kHz

switching frequency).

2. Boost Mode

When the MP2633 is in boost mode (as a

boost converter), the required inductance

value is calculated as:

MAX

_

L

S

SYS

BATT

SYS

BATT

I

f

V

)

V

V

(

V

L

Δ

×

×

−

×

=

(24)

)

MAX

(

BATT

MAX

_

L

I

%)

40

%

30

(

I

×

−

=

Δ

(25)

η

×

×

=

BATT

SYS

SYS

)

MAX

(

BATT

V

I

V

I

(26)

the peak-to-peak inductor ripple current,

which is approximately 30% of the maximum

system current and η is the efficiency.

In the worst case where the battery voltage is

3V, a 30% inductor current ripple, and a

typical

system

voltage

the

inductance

is

1.8μH

(for

the

1.2MHz

switching frequency) and 3.6µH (for the

600kHz switching frequency) when the

efficiency is 90%.

For best results, use an inductor with an

inductance

of

1.8μH

(for

the

1.2MHz

switching frequency) and 3.6µH (for the

600kHz switching frequency) with a DC

current rating that is at least 30% higher than

the maximum charge current for applications.

For higher efficiency, minimize the inductor’s

DC resistance.

current drawn from the input and the switching

noise from the device. The input capacitor

impedance at the switching frequency should be

less than the input source impedance to prevent

high-frequency-switching current from passing to

the input. For best results, use ceramic

capacitors with X5R or X7R dielectrics because

of their low ESR and small temperature

coefficients. For most applications, a 22µF

capacitor will suffice.

current ripple.

1. Charge Mode

the buck converter in charge mode. The input

current ripple is:

MAX

_

IN

TC

MAX

_

IN

TC

MAX

_

SYS

MAX

_

RMS

V

)

V

V

(

V

I

I

−

×

×

=

(27)

2.

Boost Mode

ripple small and ensures feedback loop stability.

The system current ripple is given by:

MAX

_

SYS

TC

MAX

_

SYS

TC

MAX

_

SYS

MAX

_

RMS

V

)

V

V

(

V

I

I

−

×

×

=

(28)

Since the input voltage passes to the system

boost mode have the same system current ripple.

For

the

maximum ripple current is 1A. Select the system

capacitors base on the ripple-current temperature

rise not exceeding 10°C. For best results, use

ceramic capacitors with X5R or X7R dielectrics

with low ESR and small temperature coefficients.

For most applications, use a 22µF capacitor.

high-frequency switching ripple current.

1. Charge Mode

buck converter. The output voltage ripple is then: