Analog Integrated Circuit Device Data

8

Freescale Semiconductor

33790

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

The 33790 is designed to provide the interface between

logic and the DSI bus. It accepts signals with a typical 0 V to

5.0 V logic level to control the state of the bus output (Idle

Level, Logic High Level, Logic Low Level, and High

Impedance). It detects the current drawn from the bus output

during signaling and outputs a 0 V to 5.0 V logic level

corresponding to the bus current being above (Logic [1] out)

the bus return logic [1] current or below (Logic [0] out). The

33790 contains current limiting of the bus outputs as required

by the DSI Bus specification and thermal shutdown to protect

itself from damage. Two independent DSI bus outputs are

provided by the IC.

FUNCTIONAL TERMINAL DESCRIPTION

Bus Driver and Receiver

The Wave-Shaper converts the 0 V to 5.0 V logic inputs

from DSIxF (frame) and DSIxS (signal) to a wave-shaped

signal on the DSIxO output, as shown in the timing diagrams

in Figure 2, page 2, and the truth table in Table 5. The Bus

Current Sense detects the current being drawn by the

device(s) on the bus during signalling (DSIxF=0). If the

current is above a set level, DSIxR will be high; otherwise, it

slave devices and bus delays, DSIxR should be sampled on

the falling edge of DSIxS and on the rising edge of DSIxF (for

the last return bit).

The current for the idle state is from the supply connected

250 mA per channel. During idle state, the voltage on the DSI

Internal thermal shutdown circuitry and current limit

individually protect the DSIxO outputs from shorts to battery

and ground.

Typically, the thermal shutdown occurs between 160°C

and 170°C. If the junction temperature rises above this

drivers for DSIxO are disabled by the thermal shutdown

circuitry. The output drivers remain off until the junction

temperature decreases below approximately 155°C, at which

time the thermal shutdown circuitry turns off and the outputs

are re-enabled. Each DSIxO output has a unique thermal

sense and shutdown circuit, so a short on one channel does

not affect the other channel.

Charge Pump

The charge pump uses on-board capacitors to step the

input voltage up to the voltage needed to drive the on-board

transmitter FETs. A filter/storage capacitor is connected to

CPCAP to hold the stepped-up voltage.

Input Pullups and Pulldowns

Internal current pullups are used on the DSIxF pins and

pulldowns on the DSIxS pins. If these pins are left

unconnected, their associated DSI bus will go to the unused

(high impedance) state.

Table 5. DSI Bus Truth Table

DSIxF

DSIxS

DSIxR

DSIxO

0

0

0

Not Defined

Low (1.5 V)

0

1

0

Not Defined

High (4.5 V)

0

↓

0

Return Data

Unchanged

↑

X

0

Return Data

Unchanged

1

0

0

0

High Impedance

11

0

0

Idle

X

X

1

1

High Impedance