34701 datasheet(22/38 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34701

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

THERMAL SHUTDOWN

To increase the overall safety of the system designed with

the 34701, an internal Thermal Shutdown function has been

incorporated into the switching regulator circuit. The 34701

senses the temperature of the buck regulator main switching

MOSFET (high-side MOSFET M1; see Figure 2 on page 2),

the low-side (synchronous MOSFET M2), and control circuit.

If the temperature of any of the monitored components

exceeds the limit of safe operation (Thermal Shutdown), the

switching regulator and the LDO shut down. After the

temperature falls below the value given by the Thermal

Shutdown hysteresis window, the switcher tries again to

operate.

The VOUT pull-down MOSFET M3 has an independent

Thermal Shutdown control. If the M3 temperature exceeds

the Thermal Shutdown, the M3 is turned off without affecting

the switcher operation.

The LDO pull-down MOSFET M4 has an independent

Thermal Shutdown control. If the M4 temperature exceeds

the Thermal Shutdown, the M4 will be turned off without

affecting the LDO operation.

SOFT START

A switching regulator soft start feature is incorporated in

the 34701. The soft start is active each time the IC is enabled,

VIN is reapplied, or after a fault retry. Other transient events

do not activate the soft start.

VOLTAGE MARGINING

The 34701 includes a voltage margining feature accessed

through the I2C bus. Voltage margining allows for

independent adjustment of the Switcher VOUT voltage and

the linear output VLDO. Each can be adjusted up and down

in 1.0% steps to a range of ±7.0%. This feature allows for

worst case system validation; i.e., determining the design

margin. Margining details are described in the section entitled

I2C Bus Operation, beginning on page 26 of this datasheet.

POWER SEQUENCING MODES

The power sequencing of the two outputs of this power

supply IC is in compliance with the Freescale Power QUICC

and other 32-bit microprocessor requirements. When the

input voltage is applied, the switcher and linear regulator

outputs follow the supply rail voltage during power-up and

power-down in the limits given by the microcontroller power

sequencing specification, illustrated in Figures 17 through

19. There are two possible power sequencing modes,

Standard and Inverted, as explained in more detail below.

The third mode of operation is Power Sequencing Disabled.

Figure 17. Standard Power Up/Down Sequence

in +3.3 V Supply System

∆V = 2.1 V

Max. Lead

∆V = 0.4 V

Max. Lag

∆V = 2.1 V

Max. Lead

Slope

1.0 V/ms

1.8V Start-Up

3.3 V Input Supply (I/O Voltage)

1.5 V Core Voltage

Other

Circuits

VBD

VDDL (Core)

VDDH (I/Os)

MCU

34701

3.3 V Input

VIN2

CLKSEL

FREQ

GND

SDA

SCL

2.5 V

ADDR

VIN1

LDRV

LDO

LFB

RST

PGND

INV

VBST

BOOT

VOUT

CLKSYN

Optional

EN1

EN2

VBST

VDDI

3.3 V

1.5 V

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