SLVSF02D March 2019 – May 2020 TPS23881
The following descriptions refer to the pinout and the functional block diagram.
DRAIN1-DRAIN8: Channels 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 TPS23881 uses an innovative 4-point technique to provide reliable PD detection and avoids powering an invalid load. The discovery is performed by sinking two different current levels via the DRAINn pin, while the PD voltage is measured from VPWR to DRAINn. 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 GND.
GAT1-GAT8: Channels 1-8 gate drive outputs are 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 the port is turned off by use of manual shutdown inputs. Leave floating if unused.
For improved design robustness, the current foldback functions limit the power dissipation of the MOSFET during low resistance load or short-circuit events and during the inrush period at port turn on. There is also fast overload protection comparator for major faults like a direct short that forces the MOSFET to turn off 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 measurement accuracy, ensure proper PCB layout practices are followed.
OSS: Fast shutdown, active high. This pin is internally pulled down to DGND, with an internal 1-µs to 5-µs deglitch filter.
The turn off procedure is similar to a port reset using Reset command (1Ah register). The 3-bit OSS function allows for a series of pulses on the OSS pin to turn off individual or multiple ports with up to 8 levels of priority.
RESET: Reset input, active low. When asserted, the TPS23881 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 TPS23881 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: Channel 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 0.200-Ω current sense resistor connected to GND. Used by current foldback engine and also during classification. Can be used to perform load current monitoring via ADC conversion.
When the TPS23881 performs the classification measurements, the current flows through the external MOSFETs. This avoids heat concentration in the device and makes it possible for the TPS23881 to perform classification measurements on multiple ports at the same time. 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 ADC, 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 GND.
VDD: 3.3-V logic power supply input.
VPWR: High voltage power supply input. Nominally 54 V.
AGND and DGND: Ground references for internal analog and digital circuitry respectively. Not connected together internally. Both pins require a low resistance path to the system GND plane. If a robust GND plane is used to extract heat from the device's thermal pad, these pins may be connected together through the thermal pad connection on the pcb.