MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT

MP2496M Rev.1.0

www.MonolithicPower.com

13

10/10/2015

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USB CURRENT-LIMIT SWITCH SECTION:

Current-Limit Switch

The MP2496M has a single-channel, USB,

current-limit switch. It provides built-in, soft-start

circuitry that controls the rising slew rate of the

output voltage to limit inrush current and voltage

surges.

When the load current reaches the current limit

threshold (typically 2.75A), the USB power

MOSFET switches into a foldback current limit

mode, 70% of the current limit (see Figure 4). If

the over-current limit condition lasts for more

than 3ms, the chip enters hiccup mode with 3ms

of on-time and 8.5s of off-time.

5

0

Vout(V)

Current Limit

Fold-back

Current Limit

Iout(A)

3ms

t

Figure 4: Over-Current Limit

does not exceed 70% of the current limit to avoid

triggering the foldback current limit and start-up

failure.

Output Line Drop Compensation

The MP2496M is capable of compensating for an

output voltage drop (such as a high impedance

caused by a long trace) to keep a fairly constant

5V load-side voltage. The MP2496M uses the

internal current sense output voltage of the

current-limit switch to compensate for the line drop

voltage. Since the trace resistance varies for

different

cables,

the

MP2496M

provides

selectable

line

drop

compensation

through

VDROP. The line drop compensation amplitude

increases linearly as the load current increases

and also has an upper limitation.

USB Output Over-Voltage Protection (OVP)

In order to protect the device at the cable terminal,

the USB switch’s output has a dynamic over-

voltage protection threshold. The MP2496M

adjusts the OVP threshold based on different USB

loading currents. The MP2496M has intelligent

line drop compensation and a dynamic over-

voltage protection control scheme to ensure the

voltage at the cable terminal meets the 4.75V-

5.25V specification.

USB Output Discharge

Each USB portion involves a discharge function

that provides a resistive discharge path for the

external output capacitor. The function is active

when the part is disabled (input voltage is under

UVLO, enable off) and is done in a very limited

amount of time.

Auto-Detection

The MP2496M integrates the USB dedicated

charging

port

auto-detect

function,

which

recognizes most mainstream portable devices. It

supports the following charging schemes:

•

USB battery charging specification BC1.2/

Chinese

Telecommunications

Industry

Standard YD/T 1591-2009

•

Divider mode

•

1.2V/1.2V mode

The auto-detect function is a state machine that

supports all of the above DCP charging schemes.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures. When

the silicon die temperature exceeds 165°C, the

entire chip shuts down. When the temperature

falls below its lower threshold, typically 145°C, the

chip is enabled again.