MP2637 datasheet(30/36 Pages) MPS

30 / 36 page

MP2637 –2.5A SINGLE CELL SW MODE BATTERY CHARGER WITH PPM AND 2.4A BOOST

MP2637 Rev. 1.04

www.MonolithicPower.com

8/3/2017

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

BOOST MODE OPERATION

Low-Voltage Start-Up

The minimum battery voltage required to start up

the circuit in boost mode is 2.9V. Initially, when

VSYS < VBATT, the MP2637 works in down mode.

In this mode, the synchronous P-MOSFET stops

switching and its gate connects to VBATT statically.

The P-MOSFET stays off as long as the voltage

across the parasitic CDS (VSW) is lower than VBATT.

When the voltage across CDS exceeds VBATT, the

synchronous P-MOSFET enters linear mode

allowing the inductor current to decrease and

flowing into the SYS pin. Once VSYS exceeds

VBATT, the P-MOSFET gate is released and

normal closed-loop PWM operation is initiated. In

boost mode, the battery voltage can drop to as

low as 2.5V without affecting circuit operation.

SYS Disconnect and Inrush Limiting

The MP2637 allows for true output disconnect by

eliminating body diode conduction of the internal

P-MOSFET rectifier. VSYS can go to 0V during

shutdown, drawing no current from the input

source. It also allows for inrush current limiting at

start-up, minimizing surge currents from the input

supply. To optimize the benefits of output

disconnect,

avoid

connecting

external

Schottky diode between the SW and SYS pins.

Board layout is extremely critical to minimize

voltage overshoot at the SW pin due to stray

inductance. Keep the output filter capacitor as

close as possible to the SYS pin and use very

low ESR/ESL ceramic capacitors tied to a good

ground plane.

Boost Output Voltage Setting

In boost mode, the MP2637 programs the output

voltage via the external resistor divider at FB pin,

and

provides

built-in

output

over-voltage

protection (OVP) to protect the device and other

components against damage when VSYS goes

beyond 6V. Once the output over voltage occurs,

the MP2637 turns off the boost converter. When

the voltage on VSYS drops to a normal level, the

boost converter restarts again as long as the

MODE pin remains in active status.

Boost Output Current Limiting

The MP2637 integrates a programmable output

current limit function in boost mode. If the boost

output current exceeds this programmable limit,

the output current will be limited at this level and

the SYS voltage will start to drop down. The

OLIM pin programs the current limit threshold up

to 2.4A as per the following equation:

OLIM

2400

(A)

(k ) RS1(m )



 



(7)

SYS Output Over Current Protection

The MP2637 integrates three-phase output over-

current protection.

Phase one (boost mode output current limit):

when

the

output

current

exceeds

the

programmed output current limit, the output

constant current loop controls the output current,

the output current remains at its limit of IOLIM, and

VSYS decreases.

Phase two (down mode): when VSYS drops below

VBATT+100mV

and

the

output

current

loop

remains in control, the boost converter enters

down mode and shutdown after a 120μs blanking

time.

Phase three (short circuit mode): when VSYS

drops below 3.75V (will be 2V during boost soft

start),

the

boost

converter

shuts

down

immediately once the inductor current hits the

fold-back peak current limit of the low side N-

MOSFET. The boost converter can also recover

automatically after a 1ms deglitch period.

Thermal Shutdown Protection

The thermal shutdown protection is also active in

boost mode. Once the junction temperature rises

higher than 150°C, the MP2637 enters thermal

shutdown. It will not resume normal operation

until the junction temperature drops below 120°C

MP2637 Datasheet(PDF) 30 Page - Monolithic Power Systems

MP2637 Datasheet(HTML) 30 Page - Monolithic Power Systems

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