33997 datasheet(13/20 Pages) FREESCALE

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MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

33997

SYSTEM/APPLICATION INFORMATION

INTRODUCTION

The 33997 multi-output power supply integrated circuit is

capable of operating from 6.0 V up to 26.5 V with 40 V transient

capability. It incorporates a step-down switching controller

regulating directly to 5.0 V. The 3.3 V linear regulator uses an

external pass transistor, thus reducing the power dissipation of

the integrated circuit. The 33997 also provides a 3.3 V linear

standby regulator and two 5.0 V sensor supply outputs

protected by internal low-resistance LDMOS transistors

against short-to-battery and short-to-ground.

FUNCTIONAL PIN DESCRIPTION

Switching Regulator VDDH

The switching regulator is a high-frequency (750 kHz),

conventional buck converter with integrated high-side p-

channel power MOSFET. Its output voltage is regulated to

provide 5.0 V with ±2% accuracy and it is intended to directly

power the digital and analog circuits of the Electronic Control

Module (ECM). The switching regulator output is rated for

1400 mA total output current. This current can be used by the

linear regulator VDDL and sensor supplies VREF1 and VREF2.

The 33997 switching controller utilizes "Sensorless Current

Mode Control" to achieve good line rejection and stabilize the

feedback loop. A soft-start feature is incorporated into the

33997. When the device is enabled, the switching regulator

output voltage VDDH ramps up to about half of full scale and

then takes 16 steps up to the nominal regulation voltage level

(5.0 V nominal).

3.3 V Linear Regulator VDDL

The 3.3 V linear post-regulator is powered from the 5.0 V

switching regulator output (VDDH). A discrete pass transistor is

used to the power path for the VDDL regulator. This

arrangement minimizes the power dissipation off the controller

IC. The FBL pin is the feedback input of the regulator control

loop and the DRVL pin the external NPN pass transistor base

drive. Power up, power down, and fault management are

coordinated with the 5.0 V switching regulator.

Sensor Supplies VREF1 and VREF2

The sensor supplies are implemented using a protected

switch to the main 5.0 V (switching regulator) output. The

33997 integrated circuit provides two low-resistance LDMOS

power MOSFETs connected to the switching regulator output

(VDDH). These switches have short-to-battery and short-to-

ground protection integrated into the IC. When a severe fault

conditions is detected, the affected sensor output is turned off

and the sensor Retry Timer starts to time out. After the Retry

Timer expires, the sensor supply tries to power up again.

Sensor supplies VREF can be disabled by pulling the Sensor

Enable SNSEN pin low (see Figure 7 for the VREF Retry Timer

operation).

Notes: Severe fault conditions on the VREF1 and VREF2

outputs, like hard shorts to either ground or battery, may disrupt

the operation of the main regulator VDDH. Shorts to battery

above 17 V are considered “double faults” and neither one of

the VREF outputs is protected against such conditions.

Depending on the VDDH capacitor value and its ESR value,

the severity of the short may disrupt the VDDH operation.

Keep-Alive (Standby) Regulator VKAM

The Keep-Alive Regulator VKAM (keep-alive memory) is

intended to provide power for “key off” functions such as

nonvolatile SRAM, “KeyOff" timers and controls, KeySwitch

monitor circuits, and perhaps a CAN/SCP monitor and wake-

up function. It may also power other low-current circuits

required during a “KeyOff” condition. The regulated voltage is

nominally 3.3 V. A severe fault condition on the VKAM output is

signaled by pulling the VKAMOK signal low.

VKAM Keep-Alive Operation (Standby, Power-Down

Mode)

When the EN pin is pulled low, the power supply is forced

into a low-current standby mode. In order to reduce current

drawn by the VPWR and KA_VPWR pins, all power supply

functions are disabled except for the VKAM and Enable (EN)

pins. The latter pin is monitored for the "wake-up" signal. The

switching transistor gate is actively disabled and the VDDL and

VDDH pins are actively pulled low.

Power-Up Delay Timers

Two Power-Up Delay timers are integrated into the control

section of the integrated circuit. One timer monitors the input

voltage at the VPWR input pin (see Figure 3), and the other

monitors the input voltage at the KA_VPWR input pin. In both

cases, sufficient supply voltage must be present long enough

for the timers to “time out” before the switching regulator can be

enabled.

Fault-Off Timer

If the VDDL output voltage does not reach its valid range at

the end of soft-start period, or if the VDDH or VDDL output

voltage gets below its PWROK threshold level, the Fault-Off

Timer shuts the switching regulator off until the timer “times

out” and the switching regulator retries to power up again (see

Figure 7 for Fault-Off Timer operation details).

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

33997 Datasheet(PDF) 13 Page - Freescale Semiconductor, Inc

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