down to approximately 0.375V, then the device switches to a

timed current limit mode. In timed current limit mode the

internal PFET switch is turned off after the current compara-

tor trips and the beginning of the next cycle is inhibited for

3.5us to force the instantaneous inductor current to ramp

down to a safe value. The synchronous rectifier is off in

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.

Dynamically Adjustable Output

Voltage

The LM3202 features dynamically adjustable output voltage

to eliminate the need for external feedback resistors. The

output can be set from V

voltage on the analog V

applications where peak power is needed only when the

handset is far away from the base station or when data is

being transmitted. In other instances the transmitting power

can be reduced. Hence the supply voltage to the PA can be

reduced, promoting longer battery life. See Setting the Out-

put Voltage in the Application Information section for further

details.

Thermal Overload Protection

The LM3202 has a thermal overload protection function that

operates to protect itself from short-term misuse and over-

load 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. When the

temperature drops below 125˚C, normal operation resumes.

Prolonged operation in thermal overload conditions may

damage the device and is considered bad practice.

Application Information

SETTING THE OUTPUT VOLTAGE

The LM3202 features a pin-controlled variable output volt-

age to eliminate the need for external feedback resistors. It

can be programmed for an output voltage from 1.3V (typ) to

3.16V (typ) by setting the voltage on the V

Table 1.

TABLE 1. Output Voltage Selection

V

V

V

CON

≤ 0.484

V

FB,MIN

V

V

CON

≥ 1.312

V

FB,MAX

Refer to Figure 4 for the relation between V

When the control pin voltage is between 0.556V and 1.208V,

the output voltage will vary in a monotonic fashion with

respect to the voltage on the control pin as per the above

Table 1 equation.

Internally the control pin is clamped before it is fed to the

error amplifier inputs. If voltage on the control pin is less than

0.484V, the output voltage is regulated at V

voltage is greater than 1.312V, the output is regulated at

V

INDUCTOR SELECTION

A 3.3µH inductor with saturation current rating over 1200mA

is recommended for almost all applications. The inductor’s

resistance should be less than 0.2

Ω for good efficiency. For

low dropout voltage, lower DCR inductors are advanta-

geous. Using inductors that drop by 20% in value at 1200mA

over the operating temp range is acceptable if needed to

select smallest inductor. Table 2 suggests some inductors

and suppliers.

TABLE 2. Suggested inductors and their suppliers

Model

Size (WxLxH) [mm]

Vendor

NR3015T3R3M

3.0 x 3.0 x 1.5

Taiyo-Yuden

DO3314-332MXC

3.3 x 3.3x 1.4

Coilcraft

If smaller inductance inductor is used in the application, the

LM3202 may become unstable during line and load tran-

sients and V

For low-cost applications, an unshielded bobbin inductor is

suggested. 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 a low-

noise toroidal 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 DC-DC con-

verter like the LM3202.

20141562

FIGURE 4. V

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