34921 datasheet(22/36 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34921

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

The power up sequence of the 5.0 V and 3.3 V switching

regulators is controlled such that -1.0v <= V5 - V3.3 <= 2.6v.

Figure 10 depicts the power-up sequence for the 5.0 V and

3.3 V regulators.

Figure 10. Power-Up Sequencing

VCORE LINEAR REGULATOR

The output voltage of the VCORE linear regulator is

selectable for different applications. The output is selected

with an external pull-up or pull-down, which instructs internal

logic to select the appropriate regulator set-point (refer to

Table 5). The VCORE linear regulator is available whenever

the 3.3 V supply is in stable operation.

Current limiting is implemented to provide short circuit

protection. The VCORE linear regulator is shut off by the local

thermal shutdown sensor, thus protecting the 34921 IC from

an over-temperature condition resulting from a VCORE short

circuit, but otherwise allowing VCORE to follow the 3.3 V

switching regulator.

The VCORE SUPPLY terminal is the drain or collector of

the linear regulator transistor and must be tied to the 3.3V

terminal to use the internal regulator. This allows the option

of using an external regulator if the internal 3.3 V regulator

cannot supply enough current for a particular application.

Use of an external regulator requires leaving this terminal

open, thus disabling the internal regulator. The output of the

external regulator is then connected to the VCORE terminal

for under-voltage monitoring.

DC MOTOR DRIVERS

There are two DC motor drivers on the 34921 IC: if used in

a printer application, for example, they might be the carriage

motor driver and the paper motor driver. A third drive, Motor

Driver C, can be configured as a DC motor driver or, when

B+NOM = 18 V, as a step motor driver (refer to succeeding

paragraph Step Motor Driver). Configuration bit 13

determines the mode: 0 = step mode, 1 = DC mode. A step

motor driver can only be used in B+ = 12 V to 20 V

applications. Step motor outputs are suppressed by the

internal supervisor for B+ > 20 V. The ability to use the low-

side MOSFETs for general purpose low-side outputs is

included when the system is in DC motor mode (LSOUTx).

Alternatively, the ability to use the high-side MOSFETs for

general purpose high-side outputs (HSOUTx) has been

included when the system is in step mode. (Refer to

Table 20, page 31, and Table 21, page 32.)

The DC motor drivers are pulse width modulated (PWM’d)

via inputs from the digital subsystem on the APWM and

BPWM terminals, respectively. This signal is approximately

20 kHz to 40 kHz. The DC motor driver bridge direction may

be reversed while there is significant current flowing in the

motor. The purpose of this action is to brake the motor by

rapidly lowering the current. There are pull-downs on the

PWM input terminals so that, in the event of a connection

failure, the driver will default to a safe condition.

The DC motor drivers provide high-side and low-side

current limiting. The current limits have a 0.5

µs to 6.0 µs

deglitch filter, followed by an off-timer. The off-timer shuts off

the bridge long enough to meet the 4% duty cycle goal. The

motor drivers also have thermal shutdown protection.

STEP MOTOR DRIVER C

Step motor driver C can be configured as a DC motor

driver or, when B+NOM = 18 V, as a step motor driver (refer to

succeeding paragraph Step Motor Driver). Configuration

bit 13 determines the mode: 0 = step mode, 1 = DC mode.

The ability to use the low-side MOSFETs for general purpose

low-side outputs is included when the system is in DC motor

mode (LSOUTx). Alternatively, the ability to use the high-side

MOSFETs for general purpose high-side outputs (HSOUTx)

has been included when the system is in step mode. (Refer

to Table 20, page 31, and Table 21, page 32.)

Power-Up

5.0 V Reg ON

Ref = 2.5 V

3.3 V Reg OFF

5.0 V Fault

5.0 V Reg ON

3.3 V Reg OFF

3.3 V Start

3.3 V Reg ON

Ref = 2.5 V

5.0 V Reg ON

Full Start

3.3 V Reg ON

Ref = 5.0 V

5.0 V Reg ON

3.3 V

≥ Positive

Threshold

3.3 V

≠ Positive

Threshold

V5.0 ≥ V5_3.3t

& 3.3 V > 3.3 V UV

V5.0 < V5_3.3t

V5.0 ≤ V5_3.3t

5.0 V

≥ 3.3 V

V5.0 ≥ V5_3.3t

Undervoltage (UV)

Table 5. VCORE Regulator Output Voltage Select

VCORE SELECT

VCORE_NOM

(Volts)

Tied to Ground terminal

1.5

Tied to 3.3V terminal

1.8

Floating

2.5

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