MP2617 – SINGLE CELL SWITCHING CHARGER WITH POWER PATH CONTROL

MP2617 Rev. 1.03

www.MonolithicPower.com

16

8/23/2013

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Close to 100% duty operation, BST refresh

operation makes sure the driver voltage of the

HS will be charged by turning on the LS until

negative IL hit about 400mA. If the input power is

insufficient to supply the combination of the

system load and battery charger, the DC-DC

converter will limit the total power requirement by

restricting the input voltage, input current and the

peak current through the MOSFET. The power

path management will reduce the charge current

to satisfy the external system load in priority.

According to this feature, the USB specification is

always satisfied first. Even if the charge current is

set larger than the USB input current limit, the

real charge current will be reduced as needed.

Input Limit State

If the input power is insufficient to supply the

combination of the system load and battery

charger, the MP2617 implements three input limit

control loops to reduce the charge current and

satisfy the external system load in priority. The

input in this case might be limited as follows:

input current limit, input voltage limit and DC-DC

peak current limit.

Input Current Limit: When the system current is

higher than the programmed input current limit

the input current limit loop takes the control of the

converter and regulates the input current at

constant value. When the battery voltage is over

according to the increase of the system current,

and the charge current drops down after the

BATT-to-SYS switch (40mΩ MOSFET) is fully on

process, the system voltage is slightly higher

than 3.4V, to maintain the minimum system

voltage and ensure the system operation, the

input current limit control will pull down the

charge current directly to reduce the load of the

converter so that the system current is satisfied

in priority.

Input Voltage Limit: A resistor divider from IN pin

to VLIM pin to AGND is used for the input voltage

limit control. When the voltage on VLIM pin hits

the reference voltage of 1.52V, the output of the

input voltage limit error amplifier will drop in

to control the operation duty. In this mode, the

input voltage will be clamped according to the

value set by the resistor divider. The control to

the system voltage and charge current is the

same as the one explained in the input current

limit. Charge current drops down to satisfy the

system current request first. This feature

provides a second protection to the input power

and ensures the safe operation of the input

adapter. Even if a wrong adapter is inserted, the

MP2617 can continue operation, providing the

maximum power to its load. User can program

the input voltage limit value through the resistor

divider from IN to VLIM to AGND.

Peak Current Limit: The peak current of the high

side switch of the DC-DC converter is sensed

during every cycle, it is compared to the

reference 4.2A, if the peak current hits the

threshold, the peak current limit mode is

triggered. The control of the charge current is the

same with the above two limits.

Input Current Limit Setting

The current at ILIM is a precise fraction of the

adapter input current. When a programming

resistor is connected from ILIM to AGND, the

voltage on ILIM represents the average input

current of the PWM converter. And the input

current approaches the programmed limit, ILIM

voltage reaches 1.14V.

The average input current limit can be set

through the resistor connecting from ILIM to

AGND according to the following expression:

IN_LIM

ILIM

40000

I=1.14

(mA)

R(kΩ)

×

When USB input, the input current limit is set

internally and the programmed value is invalid.

The MP2617 provides typical of 450mA input

current limit for USB2.0 specification and a

typical of 825mA for USB3.0 specification

respectively.

The user can choose to set the input current limit

through the two logic pins M0 and M1 as shown

in Table 1 according to its input specification.