LLCC68 datasheet(29/106 Pages) SEMTECH

29 / 106 page

LLCC68

Data Sheet

Rev. 1.0

DS.LLCC68.W.APP

July 2019

29 of 106

Semtech

www.semtech.com

5. Power Distribution

5.1 Selecting DC-DC Converter or LDO Regulation

Two forms of voltage regulation (DC-DC buck converter or linear LDO regulator) are available depending upon the design

priorities of the application. The linear LDO regulator is always present in all modes but the transceiver will use DC-DC when

selected. Alternatively a high efficiency DC to DC buck converter can be enabled in FS, Rx and Tx modes.

The DC-DC can be driven by two clock sources:

•

in STDBY_XOSC: RC13M is used to supply clock and the frequency is RC13M / 4 so the switching frequency of the

DC-DC converter will be 3.25 MHz

•

in FS, RX, TX: the PLL is used to supply clock and the frequency is ~5MHz; every time the command SetRFFrequency(...)

is called the divider ratio is recalculated so that the switching frequency is as close as possible to the 5 MHz target.

Unless specified, all specifications of the transceiver are given with the DC-DC regulator enabled. For applications where

cost and size are constrained, LDO-only operation is possible which negates the need for the 47nH inductor before pin 1

and the 15 μH inductor between pins 7 and 9, conferring the benefits of a reduced bill of materials and reduced board

space. The following table illustrates the power regulation options for different modes and user settings.

The user can specify the use of DC-DC by using the command SetRegulatorMode(...). This operation must be carried out in

STDBY_RC mode only.

When the DC-DC is enabled, the LDO will remain ON and its target voltage is set 50 mV below the DC-DC voltage to ensure

voltage stability for high current peaks. If the DC-DC voltage drops to this level due to high current peak, the LDO will cover

for the current need at the expense of the energy consumption of the radio which will be increased.

However, to avoid consuming too much energy, the user is free to configure the Over Current Protection (OCP) register

manually. At Reset, the OCP is configured to limit the current at 140 mA.

The OCP is configurable by steps of 2.5 mA and the default value is re-configured automatically each time the function

SetPaConfig(...) is called. If the user wants to adjust the OCP value, it is necessary to change the register as a second step after

calling the function SetPaConfig(...).

Table 5-1: Regulation Type versus Circuit Mode

Circuit Mode

Sleep

STDBY_RC

STDBY_XOSC

Regulator Type = 0

LDO

Regulator Type = 1

LDO

DC-DC + LDO

Table 5-2: OCP Configuration

OCP default

Maximum Current

0x08E7

0x38

140 mA

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