L6732_08 datasheet(12/37 Pages) STMICROELECTRONICS

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Device description

L6732

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5.3

Bypassing the LDO to avoid the voltage drop with low Vcc

If VCC ≈ 5 V the internal LDO works in dropout with an output resistance of about 1 Ω. The

maximum LDO output current is about 100 mA and so the output voltage drop is 100 mV, to

avoid this the LDO can be by passed.

5.4

Internal and external references

It is possible to set the internal/external reference and the switching frequency by setting the

proper voltage at the EAREF pin. The maximum value of the external reference depends on

the VCC: with VCC = 4 V the clamp operates at about 2 V (typ.), while with VCC greater than

5V the maximum external reference is 2.5 V (typ.).

●

VEAREF from 0 % to 80 % of VCCDR -> External reference/Fsw = 250 kHz

●

VEAREF from 80 % to 95 % of VCCDR -> VREF = 0.6V/Fsw = 500 kHz

●

VEAREF from 95 % to 100 % of VCCDR -> VREF = 0.6V/Fsw = 250 kHz

Providing an external reference from 0 V to 450 mV the output voltage will be regulated but

some restrictions must be considered:

●

OV threshold saturates to a minimum value of 300 mV (OV is tracking the

reference; tracking small references will result in a narrow threshold reducing

noise immunity)

●

The under-voltage-protection doesn't work;

●

The PGOOD signal remains low;

To set the resistor divider it must be considered that a 100 k pull-down resistor is integrated

into the device (see Figure 5.). Finally it must be taken into account that the voltage at the

EAREF pin is captured by the device at the start-up when VCC is about 4 V.

Figure 4.

Bypassing the LDO

L6732 Datenblatt(PDF) 12 Page - STMicroelectronics