MC33997 Datasheet, PDF (13/20 Pages) Motorola, Inc – Switching Power Supply with Linear Regulators

Freescale Semiconductor, Inc.
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 V_DDH
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 V_DDL and sensor supplies V_REF1 and V_REF2.
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 V_DDH 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 V_DDL
The 3.3 V linear post-regulator is powered from the 5.0 V
switching regulator output (V_DDH). A discrete pass transistor is
used to the power path for the V_DDL 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 V_REF1 and V_REF2
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
(V_DDH). 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 V_REF can be disabled by pulling the Sensor
Enable SNSEN pin low (see Figure 7 for the V_REF Retry Timer
operation).
Notes: Severe fault conditions on the V_REF1 and V_REF2
outputs, like hard shorts to either ground or battery, may disrupt
the operation of the main regulator V_DDH. Shorts to battery
above 17 V are considered “double faults” and neither one of
the V_REF outputs is protected against such conditions.
Depending on the V_DDH capacitor value and its ESR value,
the severity of the short may disrupt the V_DDH operation.
Keep-Alive (Standby) Regulator V_KAM
The Keep-Alive Regulator V_KAM (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 V_KAM output is
signaled by pulling the VKAMOK signal low.
V_KAM 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 V_PWR and KA_V_PWR pins, all power supply
functions are disabled except for the V_KAM and Enable (EN)
pins. The latter pin is monitored for the "wake-up" signal. The
switching transistor gate is actively disabled and the V_DDL and
V_DDH 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 V_PWR input pin (see Figure 3), and the other
monitors the input voltage at the KA_V_PWR 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 V_DDL output voltage does not reach its valid range at
the end of soft-start period, or if the V_DDH or V_DDL 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).
MOTOROLA ANALOG INTEGRATED CIR_FC_oUI_rT_MDE_oV_rIC_eE_ID_nA_foTA_{rmation On This Product,}
Go to: www.freescale.com
33997
13