16

NXP Semiconductors

33879

5.1.7

VDD pin

The VDD input pin is used to determine logic levels on the microprocessor interface (SPI) pins. Current from VDD is used to drive the DO

output and the pull-up current for CS. VDD must be applied for normal mode operation. The 33879 device performs Power-ON Reset with

the application of VDD.

5.1.8

VPWR pin

The VPWR pin is the battery input and Power-ON Reset to the 33879 IC. The VPWR pin has internal reverse battery protection. All internal

logic current is provided from the VPWR pin. The 33879 performs Power-ON Reset with the application of VPWR.

5.1.9

D1–D8 pins

The D1 to D8 pins are the open-drain outputs of the 33879. For high-side drive configurations, the drain pins are connected to battery

supply. In low-side drive configurations, the drain pins are connected to the low-side of the load. All outputs may be configured individually

as desired. When configured as low-side drive, the 33879 limits the positive inductive transient to 45 V.

5.1.10 S1–S8 pins

The S1 to S8 pins are the source outputs of the 33879. The source pins are connected directly to the load for high-side drive

configurations. In low-side drive configurations, the source is connected to ground. All outputs may be configured individually as desired.

When high-side drive is used, the 33879 will limit the negative inductive transient to negative 20 V.

5.1.11 Exposed Pad pin

Device performs as specified with the Exposed Pad un-terminated (floating) however, it is recommended the Exposed Pad be terminated

to pin 1 (GND) and system ground.

5.2

MCU interface description

5.2.1

Introduction

The 33879 is an eight output hardware-configurable power switch with 16-bit serial control. A simplified internal block diagram of the 33879

is shown in Figure 2. The 33879 device uses high-efficiency up-drain power DMOS output transistors exhibiting low drain-to-source ON

resistance (RDS(on) = 0.75 Ω at 25 °C typical) and dense CMOS control logic. All outputs have independent voltage clamps to provide fast

inductive turn-off and transient protection.

In operation, the 33879 functions as an eight output serial switch, serving as an MCU bus expander and buffer with fault management

and fault reporting features. In doing so, the device directly relieves the MCU of the fault management functions. This device directly

interfaces to an MCU using a SPI for control and diagnostic readout. Figure 15 illustrates the basic SPI configuration between an MCU

and one 33879.