A4408 Datasheet, PDF (1/54 Pages) Allegro MicroSystems – PWM frequency can be synchronized to external clock

A4408
Adjustable Frequency Buck or Buck-Boost Pre-Regulator with a
Synchronous Buck, 3 Internal LDOs, Watchdog Timer, NPOR, and FF0/FF1
FEATURES AND BENEFITS
• Automotive AEC-Q100 qualified
• 2.8 to 36 V_IN operating range, 40 V_IN maximum
• Buck or buck-boost pre-regulator (VREG)
• Adjustable PWM switching frequency: 250 kHz to 2.4 MHz
• PWM frequency can be synchronized to external clock
• Adjustable synchronous buck regulator (1.25 V_NOM)
• 3.3V (3V3) and 5V (V5) internal LDO regulators with
foldback short-circuit protections
• 5V (V5P) internal tracking LDO regulator with foldback
short-circuit and short-to-battery protections
• TRACK sets either 3V3 or V5 as the reference for V5P
• Power-on reset (NPOR) with fixed delay of 15 ms
• Programmable watchdog timer with activation delay
• Active-low watchdog timer enable pin (WD_ENn)
• Dual bandgaps for increased reliability: BG_VREF, BG_FAULT
• MODE pin sets the NPOR undervoltage threshold for V5
and V5P
• Fixed POK5V undervoltage threshold for V5 and V5P
• Logic enable input (ENB) for microprocessor control
• Two ignition enable inputs (ENBAT1 and ENBAT2)
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APPLICATIONS
□□Electronic Power Steering (EPS)
□□Transmission Control Units (TCU)
□□Advanced Braking Systems (ABS)
□□Emissions Control Modules
□□Other automotive applications
PACKAGE: 38-Pin eTSSOP (suffix LV)
Not to scale
DESCRIPTION
The A4408 is power management IC that uses a buck or
buck-boost pre-regulator to efficiently convert automotive
battery voltages into a tightly regulated intermediate voltage,
complete with control, diagnostics, and protections. The
output of the pre-regulator supplies a 5 V / 115 mA_MAX
tracking/protected LDO, a 3.3 V / 165 mA_MAX LDO, a
5 V / 325 mA_MAX LDO, and an adjustable output synchronous
buck regulator (1.25 V_TYP / 700 mA_DC). Designed to supply
CAN or microprocessor power supplies in high-temperature
environments, the A4408 is ideal for underhood applications.
Enable inputs to the A4408 include a logic-level (ENB) and
two high-voltage (ENBAT1 and ENBAT2) inputs. The A4408
provides flexibility by including a TRACK pin to set the
reference of the tracking regulator to either the 5 V or the 3.3 V
output, so the A4408 can be adapted across multiple platforms
with different sensors and supply rails. The MODE pin selects
the NPOR undervoltage threshold for the V5 and V5P outputs.
Diagnostic outputs from the A4408 include a power-on-reset
output (NPOR). POK5V indicates the status of the 5 V and
5 V protected LDOs. Fault Flag 0 (FF0) and Fault Flag 1 (FF1)
retain the last fault to reset the microcontroller. Dual bandgaps,
one for regulation and one for fault checking, improve long-
term reliability of the A4408.
The A4408 contains a watchdog timer that can be programmed
to accept a wide range of clock frequencies (WD_ADJ). The
watchdog timer has a fixed activation delay to accommodate
processor startup. The watchdog timer has an enable/disable pin
(active low, WD_ENn) to facilitate initial factory programming
or field reflash programming.
Protection features include under- and overvoltage lockout on
all four CPU supply rails. In case of a shorted output, all linear
regulators feature foldback overcurrent protection. In addition,
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5.35 V
(VREG)
Buck-Boost
Pre-Regulator
3.3 V LDO
(3V3)
with Foldback
Protection
1.25 V
(1V25)
Synchronous Buck
Regulator
Programmable
Watchdog Timer
with Activation
Delay
5 V LDO
(V5)
with Foldback
Protection
Dual
Bandgaps
Charge
Pump
FF0 / FF1,
UV, HIC,
TSD, WD
POK5V
Output
3V3
NPOR
Output
V5
Tracking
Control
2:1 MUX
5 V LDO
(V5P)
with Tracking,
Foldback, and
Short to V_BAT
Protection
REF
A4408-DS, Rev. 1
Figure 1: A4408 Simplified Block Diagram
January 27, 2017