5.1 Detailed Pin Description

The following descriptions refer to the pinout and the functional block diagram.

DRAIN1-DRAIN8: Port 1-8 output voltage monitor and detect sense. Used to measure the port output voltage, for port voltage monitoring, port power good detection and foldback action. Detection probe currents also flow into this pin.

The TPS2388 uses an innovative 4-point technique to provide reliable PD detection. The discovery is performed by sinking two different current levels via the DRAINn pin, while the PD voltage is measured from VPWR to DRAINn. The 4-point measurement provides the capability to avoid powering a capacitive or legacy load. Also, while in semiauto mode, if prior to starting a new detection cycle the port voltage is >2.5 V, an internal 100-kΩ resistor is connected in parallel with the port and a 400-ms detect backoff period is applied to allow the port capacitor to be discharged before the detection cycle starts.

There is an internal resistor between each DRAINn pin and VPWR in any operating mode except during detection or while the port is ON. If the port n is not used, DRAINn can be left floating or tied to AGND.

GAT1-GAT8: Port 1-8 gate drive output is used for external N-channel MOSFET gate control. At port turn on, it is driven positive by a low current source to turn the MOSFET on. GATn is pulled low whenever any of the input supplies are low or if an overcurrent timeout has occurred. GATn is also pulled low if its port is turned off by use of manual shutdown inputs. Leave floating if unused.

For a robust design, a current foldback function limits the power dissipation of the MOSFET during low resistance load or a short-circuit event. During inrush, the foldback mechanism measures the port voltage across VPWR and DRAINn to reduce the current limit threshold as shown in Figure 17.

When I_CUT threshold is exceeded while a port is on, a timer starts. During that time, linear current limiting ensures the current does not exceed I_LIM combined with current foldback action. When the timer reaches its t_OVLD (or t_START if at port turn on) limit, the part shuts off. When the port current goes below I_CUT, the counter counts down at a rate 1/16^th of the increment rate and it must reach a count of 0 before the port can be turned on again.

The fast overload protection is for major faults like a direct short. This forces the MOSFET into current limit in less than a microsecond.

The circuit leakage paths between the GATn pin and any nearby DRAINn pin, GND or Kelvin point connection must be minimized (<250 nA), to ensure correct MOSFET control.

INT: This interrupt output pin asserts low when a bit in the interrupt register is asserted. This output is open-drain.

KSENSA, KSENSB, KSENSC, KSENSD: Kelvin point connection used to perform a differential voltage measurement across the associated current sense resistors.

Each KSENS is shared between two neighbor SEN pins as following: KSENSA with SEN1 and SEN2, KSENSB with SEN3 and SEN4, KSENSC with SEN5 and SEN6, KSENSD with SEN7 and SEN8. To optimize the accuracy of the measurement, take care with the PCB layout to minimize the impact of the PCB traces' resistance.

OSS: Fast shutdown, active high. This pin is internally pulled down to DGND, with an internal 1-µs to 5-µs deglitch filter.

The Port Power Priority/ICUT Disable register is used to determine which port is shut down in response to an external assertion of the OSS fast shutdown signal. The turn off procedure is similar to a port reset using Reset command (1Ah register).

RESET: Reset input, active low. When asserted, the TPS2388 resets, turning off all ports and forcing the registers to their power-up state. This pin is internally pulled up to VDD, with internal 1-µs to 5-µs deglitch filter. The designer can use an external RC network to delay the turn-on. There is also an internal power-on-reset which is independent of the RESET input.

SCL: Serial clock input for I²C bus.

SDAI: Serial data input for I²C bus. This pin can be connected to SDAO for non-isolated systems.

SDAO: Open-drain I²C bus output data line. Requires an external resistive pull-up. The TPS2388 uses separate SDAO and SDAI lines to allow optoisolated I²C interface. SDAO can be connected to SDAI for non-isolated systems.

A4-A1: I²C bus address inputs. These pins are internally pulled up to VDD. See Pin Status Register for more details.

SEN1-8: Port current sense input relative to KSENSn (see KSENSn description). A differential measurement is performed using KSENSA-D Kelvin point connection. Monitors the external MOSFET current by use of a 0.255-Ω current sense resistor connected to DGND. Used by current foldback engine and also during classification. Can be used to perform load current monitoring via A/D conversion.

Note that a classification is done while using the external MOSFET so that doing a classification on more than one port at same time is possible without overdissipation in the TPS2388. For the current limit with foldback function, there is an internal 2-µS analog filter on the SEN1-8 pins to provide glitch filtering. For measurements through an A/D converter, an anti-aliasing filter is present on the SEN1-8 pins. This includes the port-powered current monitoring, port policing, and DC disconnect.

If the port is not used, tie SENn to AGND.

VDD: 3.3-V logic power supply input.

VPWR: High voltage power supply input. Nominally 48 V.