L6364 datasheet(38/60 Pages) STMICROELECTRONICS

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17.3.4

SLEEP state

The SLEEP state is reached after 1ms by setting the DCDC:DIS bit via the microcontroller. In the SLEEP state no

current is drawn by the DC-DC converter on VPLUS or V3V3, and the switch control blocks are depowered. The

SLEEP state is left by resetting the DCDC:DIS bit, or during a L6364 reset, that is when VV3V3 < VPOR.

17.3.5

BYPASS state

The BYPASS state is equivalent to the STARTUP state, and is reached after 1 ms by setting the DCDC:BYP bit

via the microcontroller.

In this mode, the ISTARTUP current source is permanently enabled and the voltage on VDCDC is held at VSTARTUP.

Power to the devices on the V3V3 or V5V pins is now provided via the inductor and linear regulators. Leaving

the BYPASS state is achieved by clearing the DCDC:BYP bit, whereby normal operation of the DC-DC converter

resumes after 40 μs.

This operation mode can be used if a device is operated at times in a low current consumption state, or

suppression of converter switching noise is required for a temporary period.

17.4

Converter external component consideration

17.4.1

Minimum supply voltage

The DC-DC converter has a minimum off-time per cycle, which leads to a maximum duty of:

DMAX = 1 − (150 ns × fSET);

eg. at fSET = 1 MHz

⇒ DMAX = 0.85.

Figure 15. Minimum supply voltage

Current

Voltage

VSET

VDIODE

Resistive Losses

VSET / DMAX

Minimum VVPLUS

The supply voltage (VVPLUS) required to reach a nominal output voltage (VSET) is given by:

VVPLUS = VSET / DMAX + VDIODE + IOUT × [RCOIL / DMAX + RHIGH + (1/DMAX−1) × (RSHUNT+ RLOW)]

For VSET= 8.6 V, VDIODE=1 V, IOUT= 50 mA, RCOIL= 2 Ω, RHIGH= RLOW= 20 Ω, RSHUNT= 1.5 Ω, DMAX= 90%

a supply voltage of 11.80 V is required to ensure that the nominal set voltage can be reached for all devices over

the entire temperature range.

Note:

At very low supply voltages, where the duty cycle approaches DMAX, an increased ripple on the VDCDC supply

may occur.

17.4.2

Coil current limitation protection

Where the coil current exceeds ILIMIT at the start of a cycle, that cycle is aborted. The current is checked again

every 200 ns and a normal cycle is started once the coil current is below ILIMIT.

L6364

Converter external component consideration

DS13363 - Rev 4

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