34701 datasheet(25/38 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34701

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Single 5.0 V Supply, VIN1 = VIN2, or Dual Supply VIN1

≠

VIN2

The LDO supplies the microprocessor I/O voltage. The

switcher supplies the core (e.g., 1.5 V nominal) (see

Figure 18, page 23).

Power-Up

This condition depends upon the regulator current limit,

load current and capacitance, and the relative rise times of

the VIN1 and VIN2 supplies. There are two cases:

1. LDO rises faster than VOUT. The LDO uses control

methods (1) and (2) described in the section Methods

of Control on page 23.

2. VOUT rises faster than LDO. The switcher uses control

methods (5) and (6) described in the section Methods

of Control on page 23.

Power-Down

This condition depends upon the regulator load current

and capacitance and the relative fall times of the VIN1 and

VIN2 supplies. There are two cases:

1. VOUT falls faster than LDO. The LDO uses control

methods (1) and (2) described in the section Methods

of Control on page 23.

In the case VIN1 = VIN2, the intrinsic operation turns

on both the Buck High-Side MOSFET and the LDO

external Pass MOSFET, and discharges the LDO load

capacitor into the VIN supply.

2. LDO falls faster than VOUT . The switcher uses control

methods (5) and (6) described in the section Methods

of Control on page 23.

Shorted Load

1. VOUT shorted to ground. The LDO uses method (1)

and (2) described in the section Methods of Control on

page 23.

2. LDO shorted to ground. The switcher uses control

methods (5) and (6) described in the section Methods

of Control on page 23.

3. VIN1 shorted to ground. Device is not working.

4. VIN2 shorted to ground with VIN1 and VIN2 different.

This is equivalent to the switcher output shorted to

ground.

5. VOUT shorted to supply. No load protection. 34701 is

protected by current limit and Thermal Shutdown.

6. LDO shorted to supply. No load protection. 34701 is

protected by current limit and Thermal Shutdown.

INVERTED OPERATING MODE

Single 3.3 V Supply, VIN = VIN1 = VIN2 = 3.3 V

The 3.3 V supplies the microprocessor I/O voltage, the

LDO supplies core voltage (e.g., 1.5 V nominal), and the

switcher VOUT operates independently. Power sequencing

depends only on the normal LDO intrinsic operation to control

the Pass MOSFET.

Power-Up

When VIN is rising, initially LDO is below the regulation

point and the Pass MOSFET is on. In order not to exceed the

2.1 V differential requirement between the I/O (VIN) and the

core (LDO), the LDO must start up at 2.1 V or less and be

able to maintain the 2.1 V or less differential. The maximum

slew rate for VIN is 1.0 V/ms.

Power-Down

When VIN is falling, LDO falls below the regulation point;

therefore, the Pass MOSFET is on. In the case where LDO is

falling faster than VIN, the Pass MOSFET attempts to

maintain LDO. In the case where VIN is falling faster than

LDO, the Pass MOSFET is also on, and the LDO load

capacitor is discharged through the Pass MOSFET to VIN.

Thus, provided VIN does not fall too fast, the core voltage

(LDO) does not exceed the I/O voltage (VIN) by more than

maximum of 0.4 V.

Shorted Load

1. LDO shorted to ground. This will cause the I/O voltage

to exceed the core voltage by more than 2.1 V. No load

protection.

2. VIN shorted to ground. Until the LDO load capacitance

is discharged, the core voltage exceeds the I/O voltage

by more than 0.4 V. By the intrinsic operation of the

LDO, the load capacitor is discharged rapidly through

the Pass MOSFET to VIN.

3. LDO shorted to supply. No load protection.

Single 5.0 V Supply, VIN1 = VIN2, or Dual Supply VIN1

≠

VIN2

The switcher VOUT supplies the microprocessor I/O

voltage. The LDO supplies the core (e.g., 1.5 V nominal) (see

Figure 19, page 23).

Power-Up

This condition depends upon the regulator current limit,

load current and capacitance, and the relative rise times of

the VIN1 and VIN2 supplies. There are two cases:

1. VOUT rises faster than LDO. The switcher VOUT uses

control methods (1) and (2) described in the section

Methods of Control on page 23.

2. LDO rises faster than VOUT . The LDO uses control

methods (5) and (6) described in the section Methods

of Control on page 23.

Power-Down

This condition depends upon the regulator load current

and capacitance and the relative fall times of the VIN1 and

VIN2 supplies. There are two cases:

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