EM357-RTR datasheet(207/241 Pages) SILABS

207 / 241 page

Rev 1.3

207

16. Integrated Voltage Regulator

The EM35x integrates two low dropout regulators to provide 1.8 V and 1.25 V power supplies as detailed in

Table 16.1. The 1V8 regulator supplies the analog and memories, and the 1V25 regulator supplies the digital core.

In deep sleep, the voltage regulators are disabled.

When enabled, the 1V8 regulator steps down the pads supply voltage (VDD_PADS) from a nominal 3.0 V to 1.8 V.

The regulator output pin (VREG_OUT) must be decoupled externally with a suitable capacitor. VREG_OUT should

be connected to the 1.8 V supply pins VDDA, VDD_RF, VDD_VCO, VDD_SYNTH, VDD_IF, and VDD_MEM. The

1V8 regulator can supply a maximum of 50 mA.

When enabled, the 1V25 regulator steps down VDD_PADS to 1.25 V. The regulator output pin (VDD_CORE, Pin

17) must be decoupled externally with a suitable capacitor. It should connect to the other VDD_CORE pin (Pin 44).

The 1V25 regulator can supply a maximum of 10 mA.

The regulators are controlled by the digital portion of the chip as described in "6. System Modules" on page 35.

An example of decoupling capacitors and PCB layout can be found in the application notes (see the various Ember

EM35x reference design documentation).

Table 16.1. Integrated Voltage Regulator Specifications

Spec Point

Min

Typ

Max

Units

Comments

Supply range for regulator

2.1

3.6

VDD_PADS

1V8 regulator output

–5%

1.8

+5%

Regulator output after initialization

1V8 regulator output after

reset

–5%

1.75

+5%

Regulator output after reset

1V25 regulator output

–5%

1.25

+5%

Regulator output after initialization

1V25 regulator output after

reset

–5%

1.45

+5%

Regulator output after reset

1V8 regulator capacitor

2.2

µF

Low ESR tantalum capacitor

ESR greater than 2



ESR less than 10



de-coupling less than 100 nF ceramic

1V25 regulator capacitor

1.0

µF

Ceramic capacitor (0603)

1V8 regulator output current

Regulator output current

1V25 regulator output



current

Regulator output current

No load current

600

µA

No load current (bandgap and regulators)

1V8 regulator current limit

200

Short circuit current limit

1V25 regulator current limit

Short circuit current limit

1V8 regulator start-up time

µs

0 V to POR threshold

2.2 µF capacitor

1V25 regulator start-up time

µs

0 V to POR threshold

1.0 µF capacitor

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