EFP01 datasheet(20/158 Pages) SILABS

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3.2.3.3 Maximum Output Current

After startup, the maximum output current for LDO B and LDO C is set by the LDOB_IGAIN and LDOC_IGAIN fields in the

LDOB_CTRL and LDOC_CTRL registers, respectively. The LDOx_IGAIN fields should be set to the required output current plus mar-

gin, but no higher than necessary. LDOx_IGAIN can be computed as follows:

Note: The Maximum Output Current formula below provides useful guidance but is not a guarantee of performance. The final authority

for the Maximum Output Current will be the Output Load Current specifications in the Electrical Characteristics tables.

LDOx_IGAIN = ROUND

(17-

VOUT

2.76 ×

IOUT _MAX )

At startup, and prior to the LDO reaching its target voltage, the available output current for LDO B and LDO C is determined by the

LDOB_VMIN and LDOC_VMIN fields in the LDOB_CTRL and LDOC_CTRL registers, respectively. To ensure the LDO output current

at startup is always at least the desired amount (as configured by LDOx_IGAIN, above), the settings for the LDOx_VMIN fields should

be programmed based on the output target voltage as shown below:

Table 3.6. LDOx_VMIN Settings

VOUT Range

LDOx_VMIN Setting

VOUT ≥ 2.7V

2.4V ≤ VOUT < 2.7V

2.0V ≤ VOUT < 2.4V

VOUT < 2.0V

Table 3.7 Example LDOx_IGAIN and LDOx_VMIN settings on page 20 shows the recommended LDOx_IGAIN and LDOx_VMIN set-

tings for some example applications. Note that in the calculations below, IOUT_MAX has been increased by 20% to provide some margin.

Table 3.7. Example LDOx_IGAIN and LDOx_VMIN settings

VOUT (V)

IOUT_MAX (mA)

LDOx_IGAIN

LDOx_VMIN

1.8

100

3.0

100

1.2 (LDO B only)

3.2.3.4 LDO Current Limiting

On EFP01, the current limit is controlled by forcing a minimum time between the start of pulse events (TSW_MIN) and is configured by

the BK_IRI_CON bitfield in the BK_CTRL2 register (for LDO B) or the VOC_IRI_CON bitfield in the LDOC_BB_CTRL register (for LDO

C). The (IBATT_LIMIT) can be determined from the IRI_CON setting as follows:

IBATT_LIMIT =

IOUT_MAX

(2 × IRI_CON

+ 1)

where IOUT_MAX is determined by LDOx_IGAIN as shown in 3.2.3.3 Maximum Output Current.

Because the current limit is essentially current-starving the output, most applications will likely want to disable the current limit after the

output is stable (which can be determined by polling the STATUS_LIVE.VOx_INREG_LIVE bits).

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