The TCAN284XX and TCAN285XX families both share two integrated fixed voltage LDOs, a variable voltage integrated LDO controller, and four high side switches as power management subsystems to the main IC.

The integrated LDOs represent VCC1 and VCC2 output pins on the TCAN284XX/TCAN285XX device. VCC1 is considered the primary LDO of the system. The device cannot enter standby until VCC1 is at a proper level for a preset period of time and many subsystems are internally referenced or powered directly by VCC1 including SPI operation and logic interface voltage ranges. The TCAN284X5/TCAN285X5 variants of the IC VCC1 has a 5V output and is rated to supply up to 250mA while the TCAN284X3/TCAN285X3 variants of the IC, VCC1 has a 3.3V output and is rated to the same 250mA. If the interfacing controller is a 3.3V device, then the TCAN284X3/TCAN285X3 variant is chosen and a variant ending in “5” is for 5V interfaces. VCC1 can be accessed for routing to external loads from header J7 on the board and configured at register addresses Ch, Dh, and Eh. VCC2 is powered by the second LDO which regardless of device variant is always 5V rated up to 200mA of output current. VCC2 can be accessed for external loads from header J34 and can be configured at register address Ch.

The LDO controller is comprised of 3 pins (VEXMON, VEXCTRL, VEXCC) that are connected to an external PNP transistor with a β of 50 to 500. VEXMON is the voltage monitor pin and is connected to both the emitter of the PNP and the VSUP pin through a shunt resistor. The shunt resistor sets the current limit of the of the external LDO. VEXCTRL is connected to the base of the PNP transistor and controls the external LDO. VEXCC is the connected to the collector of the PNP and acts as the output of the VEXCC.

Figure 2-1 Stand-Alone Configuration for VEXCC

In applications where VEXCC is not used, make sure that VEXMON is not left floating and is connected to VSUP. This external LDO controller can support 1.8V, 2.5V, 3.3V, and 5V output levels with up to 350mA of rated current. The controller can be accessed through header J13 and configured at register address Dh.

In some applications, the current allowed from any of the LDO, integrated, or otherwise, may not be enough. The TCAN284XX/TCAN285XX designs did take this into consideration and gave the ability of load sharing; therefore, increasing the total available current output for a specific load. There is simple test with the EVM where the first thing done is to configure VEXCC to be on (the EVM is off by default). Change the voltage control method to be load sharing. This can be accessed at the register address Dh. After the device has been properly configured, shunting J19 shorts VCC1 and VEXCC together, and a load sharing application can now be further tested.

Figure 2-2 VCC1 + VEXCC Load Sharing

The other main power management feature of these devices comes in the form of 4 high side switches, labeled as HSS. The switches are high voltage tolerant and are commonly attached to the same voltage supply as VSUP through the VHSS pin. The switches can act as a simple load switch where each switch can carry up to 100mA. All HSS outputs 1 through 4 can be accessed at header block J2. The HSS outputs can be shorted to allow for larger currents, if all 4 outputs are shorted up to 400mA of current can be delivered to an off-board load. Easy access to short outputs is located on header block J2. Each switch has multiple modes of operation as the switch can be turned off and on, controlled by PWM1 through PWM4, controlled by Timer1 or Timer2, or direct drive through WAKE3 pin with a fast or slow slew rate setting. HSS1 and HSS2 can be configured at register address 1Eh. HSS3 and HSS4 can be configured at register address 4Dh with additional configuration options for both located at 4Fh.