EM357-RTR Datasheet, PDF (207/241 Pages) Silicon Laboratories – High-Performance, Integrated ZigBee/802.15.4 System-on-Chip

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
Supply range for regulator
2.1
1V8 regulator output
–5% 1.8
1V8 regulator output after
reset
–5% 1.75
1V25 regulator output
–5% 1.25
1V25 regulator output after –5% 1.45
reset
1V8 regulator capacitor
2.2
1V25 regulator capacitor
1.0
1V8 regulator output current 0
1V25 regulator output 
current
No load current
0
600
1V8 regulator current limit
200
1V25 regulator current limit
25
1V8 regulator start-up time
50
1V25 regulator start-up time
50
Max
3.6
+5%
+5%
Units
Comments
V VDD_PADS
V Regulator output after initialization
Regulator output after reset
+5%
+5%
V Regulator output after initialization
Regulator output after reset
µF Low ESR tantalum capacitor
ESR greater than 2 
ESR less than 10 
de-coupling less than 100 nF ceramic
µF Ceramic capacitor (0603)
50
mA Regulator output current
10
mA Regulator output current
µA No load current (bandgap and regulators)
mA Short circuit current limit
mA Short circuit current limit
µs 0 V to POR threshold
2.2 µF capacitor
µs 0 V to POR threshold
1.0 µF capacitor
Rev 1.3
207