AN4501 datasheet(22/48 Pages) STMICROELECTRONICS

22 / 48 page

Selection of the inductor

AN4501

22/48

DocID026394 Rev 1

4.6

Input current limiter

The L99LD01 offers a monitoring of the inductor current, which is sensed through the shunt

resistor RSHUNT. This feature ensures that the inductor current is always below the

saturation current if RSHUNT is correctly selected:

The threshold of the input current limitation is set by default to:

where GLAMP (typ. value ~ 9.8, refer to datasheet of the L99LD01) is the gain of the linear

amplifier.

Figure 8. A shunt resistor is used to monitor the inductor current during the on-state

The input current limiter can be configured by a specific SPI control register from

with a step of

4.7

Limit of the continuous conduction mode

As stated in the introduction, all the considerations are valid only if the boost converter

works in CCM, in other words, inductor current does not decay to zero.

An operation in discontinuous conduction mode (DCM) must be sometimes avoided,

because of the increased electromagnetic emission. Indeed, when the output current or the

duty cycle are low enough to allow the inductor current to decay to zero, we can observe a

IN PUT MAX

LAMP

SHUNT

--------------------------------------------------

0.5V

LAM P

SHUNT

--------------------------------------------------

3.5V

LAM P

SHUNT

--------------------------------------------------

LAM P

SHUNT

--------------------------------------------------------------

AN4501 Datasheet(PDF) 22 Page - STMicroelectronics