User's Manual

Confidential
INTERFACE DESCRIPT
21(31)
Document number Revision
1/155 19-KRD 104 1025 Uen PA4
5.1.2 3V3
Function: Daughter card reference voltage
Description: Host reference to protection circuit & USB (3.3V)
Pin Numbers: 21
Signal Names: 3V3 [host⇒daughter card]
If not used: Required
Details:
The host supplies a 3.3V regulated supply to the Daughter Card for two primary functions
:
• reference supply for the undervoltage / short circuit protection circuitry
• input for the USB interface
Electrical Characteristics:
Parameter Condition Min Nom Max Unit
Voltage 3.30 V
Ripple 100 mV
5.1.3 VREF
Function: Voltage Reference
Description: Core digital voltage reference from modem.
Pin Number: 3
Signal Name: VREF [modem⇒host]
If not used: Required
Details:
VREF is supplied as a reference voltage from the modem. This reference is the modem’s
core digital supply voltage at a nominal 2.80V.
The interface is capable of sourcing 200uA and is intended primarily for situations where
host interface circuitry is required to be level shifted to maintain wireless modem signal
level compatibility. If more current is required by the host, a current amplifier must be
implemented.