LAN8710A Datasheet, PDF (38/82 Pages) SMSC Corporation – Small Footprint MII/RMII 10/100 Ethernet Transceiver with HP Auto-MDIX and flexPWR Technology

Small Footprint MII/RMII 10/100 Ethernet Transceiver with HP Auto-MDIX and flexPWR^® Technology
Datasheet
3.7.4
3.7.4.1
3.7.4.2
REGOFF: Internal +1.2V Regulator Configuration
The incorporation of flexPWR technology provides the ability to disable the internal +1.2V regulator.
When the regulator is disabled, an external +1.2V must be supplied to the VDDCR pin. Disabling the
internal +1.2V regulator makes it possible to reduce total system power, since an external switching
regulator with greater efficiency (versus the internal linear regulator) can be used to provide +1.2V to
the transceiver circuitry.
Note:
Because the REGOFF configuration strap shares functionality with the LED1 pin, proper
consideration must also be given to the LED polarity. Refer to Section 3.8.1.1, "REGOFF and
LED1 Polarity Selection," on page 39 for additional information on the relation between
REGOFF and the LED1 polarity.
Disabling the Internal +1.2V Regulator
To disable the +1.2V internal regulator, a pull-up strapping resistor should be connected from the
REGOFF configuration strap to VDD2A. At power-on, after both VDDIO and VDD2A are within
specification, the transceiver will sample REGOFF to determine whether the internal regulator should
turn on. If the pin is sampled at a voltage greater than V_IH, then the internal regulator is disabled and
the system must supply +1.2V to the VDDCR pin. The VDDIO voltage must be at least 80% of the
operating voltage level (1.44V when operating at 1.8V, 2.0V when operating at 2.5V, 2.64V when
operating at 3.3V) before voltage is applied to VDDCR. As described in Section 3.7.4.2, when
REGOFF is left floating or connected to VSS, the internal regulator is enabled and the system is not
required to supply +1.2V to the VDDCR pin.
Enabling the Internal +1.2V Regulator
The +1.2V for VDDCR is supplied by the on-chip regulator unless the transceiver is configured for the
regulator off mode using the REGOFF configuration strap as described in Section 3.7.4.1. By default,
the internal +1.2V regulator is enabled when REGOFF is floating (due to the internal pull-down
resistor). During power-on, if REGOFF is sampled below V_IL, then the internal +1.2V regulator will turn
on and operate with power from the VDD2A pin.
3.7.5
nINTSEL: nINT/TXER/TXD4 Configuration
The nINT, TXER, and TXD4 functions share a common pin. There are two functional modes for this
pin, the TXER/TXD4 mode and nINT (interrupt) mode. The nINTSEL configuration strap is latched at
POR and on the rising edge of the nRST. By default, nINTSEL is configured for nINT mode via the
internal pull-up resistor.
Note:
Because the nINTSEL configuration strap shares functionality with the LED2 pin, proper
consideration must also be given to the LED polarity. Refer to Section 3.8.1.2, "nINTSEL and
LED2 Polarity Selection," on page 39 for additional information on the relation between
nINTSEL and the LED2 polarity.
Revision 1.4 (08-23-12)
38
DATASHEET
SMSC LAN8710A/LAN8710Ai