LM3203

SNVS355D – MAY 2005 – REVISED APRIL 2013

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repeated until the load is reduced and the output voltage exceeds approximately 0.375V. Therefore, the device

may not startup if an excessive load is connected to the output when the device is enabled. The synchronous

rectifier is off in the timed current limit mode. Timed current limit prevents the loss of current control seen in

some products when the output voltage is pulled low in serious overload conditions. This timed current limit

A current limit is also provided for the NFET. This is approximately

−500mA. Both the NFET and the PFET are

turned off in negative current limit until the PFET is turned on again at the beginning of the next cycle. The

negative current limit inhibits buildup of excessive negative inductor current.

In the Bypass mode, the bypass current limit is 1000mA (typ.). The output voltage drops when the bypass

current limit kicks in.

Thermal Overload Protection

The LM3203 has a thermal overload protection function to protect the device from short-term misuse and

overload conditions. When the junction temperature exceeds around 150°C, the device inhibits operation. Both

the PFET and the NFET are turned off in PWM mode, and the Bypass PFET is turned off in Bypass mode. When

the temperature drops below 130°C, normal operation resumes. Prolonged operation in thermal overload

conditions may damage the device.

APPLICATION INFORMATION

SETTING THE OUTPUT VOLTAGE

The LM3203 features a pin-controlled variable feedback voltage. It can be programmed for an output voltage

(1)

If the target voltage is less than 0.8V, the output voltage may not be regulated due to the required on-time being

curve is for a typical part and there could be part to part variation for output voltages less than 0.8V over the

internal bias circuits are still active.

INDUCTOR SELECTION

A 3.3µH inductor with saturation current rating over 940mA is recommended for almost all applications. The

inductor resistance should be less than 0.3

Ω for better efficiency. Table 1 lists suggested inductors and

suppliers.

Table 1. Suggested Inductors and Suppliers

Model

Size (WxLxH) [mm]

Vendor

DO3314-332MX

3.3 x 3.3 x 1.4

Coilcraft

NR3015T3R3M

3.0 x 3.0 x 1.5

Taiyo- Yuden

A 2.2uH inductor can be used if maximum current in PWM mode is 300mA. For low-cost applications, an

unshielded bobbin inductor can be used. For noise-critical applications, a toroidal or shielded-bobbin inductor

should be used. A good practice is to layout the board with footprints accommodating both types for design

flexibility. This allows substitution of an unshielded inductor, in the event that noise from low-cost bobbin models

is unacceptable. Saturation occurs when the magnetic flux density from current through the windings of the

inductor exceeds what the inductor’s core material can support with a corresponding magnetic field. This can

cause poor efficiency, regulation errors or stress to a DC-DC converter like the LM3203.

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