LAN8740A Datasheet, PDF (35/136 Pages) Microchip Technology – Small Footprint MII/RMII 10/100 Energy Efficient Ethernet Transceiver with HP Auto-MDIX and flexPWR® Technology

LAN8740A/LAN8740Ai
3.7.4 REGOFF: INTERNAL +1.2 V REGULATOR CONFIGURATION
The incorporation of flexPWR technology provides the ability to disable the internal +1.2 V regulator. When the regulator
is disabled, an external +1.2 V must be supplied to the VDDCR pin. Disabling the internal +1.2 V 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 +1.2 V 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, "LEDs" for additional information on the rela-
tion between REGOFF and the LED1 polarity.
3.7.4.1 Disabling the Internal +1.2 V Regulator
To disable the +1.2 V internal regulator, a pull-up strapping resistor should be connected from the REGOFF configura-
tion 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 +1.2 V to the VDDCR pin. The VDDIO voltage must
be at least 80% of the operating voltage level (1.44 V when operating at 1.8 V, 2.0 V when operating at 2.5 V, 2.64 V
when operating at 3.3 V) 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 +1.2 V to the
VDDCR pin.
3.7.4.2 Enabling the Internal +1.2 V Regulator
The +1.2 V 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 +1.2 V 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 +1.2 V 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: In order to utilize EEE, the nINT/TXER/TXD4 pin must be configured as TXER/TXD4.
Note:
Due to the multiplexing of nINT and TXER on the same pin, when EEE and WoL are both enabled, nINT
and/or nPME must be multiplexed on LED1 and/or LED2. Refer to Section 3.6, "Interrupt Management"
and Section 3.8.4, "Wake on LAN (WoL)" for additional information.
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 3.8.1.6, "nINTSEL and LED2 Polarity Selection"
for additional information on the relation between nINTSEL and the LED2 polarity.
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DS00001987A-page 35