L9758 Datasheet L9758, L9758TR, E-L9758BBTR | P22-P24

Functional description L9758

22/30 DocID14273 Rev 5

The V

DDL

voltage is selectable with the VPROG3 pin: 2.5 V if connected to GND and 3.3 V

if left open (an internal pull-up is present). V

CORE

voltage is programmable connecting an

external resistor divider at the feedback pin (VCORE_FDBK).

Once programmed to a value at power-up, this value cannot change during the power cycle.

Purposely the system runs at a single fixed value for V

DDL

and V

CORE

for the life of the

product.

All the linear regulators start with a controlled slew rate when the pre-regulated voltage

reaches V

DDL_ENUP

threshold as indicated in the electrical characteristics table. All the

linear regulators are short circuit protected with a limited current.

5.4 Tracking regulators

Four low drop-out tracking regulators (VSA, VSB, VSC and VSD) are supplied by the output

of the switching pre-regulator. They track the output voltage of the VDD5 linear regulator

with the accuracy as specified in the electrical characteristic table.

The VSA regulator also tracks an external voltage reference (TRACK_REF pin) and the

tracking voltage is selected by the REF_SEL pin.

If REF_SEL is tied High (5 V) then V

TRK_REF

is tracked. If REF_SEL is left open then V

DD5

is tracked. There is an internal pull-down on REF_SEL.

The tracking supplies are intended to drive loads that are external to the ECU so they are

short circuit protected with the current limited. The outputs of the tracking regulators also

withstand short circuit to the battery.

A short circuit to GND, continuous or intermittent on one tracking supply will not affect any

other supply, including the preregulator output voltage V

. In addition to these requirements,

all sensor supplies shall be capable of operating with up to a 15 μF load on the supply line.

This load may be present during initial startup, or be applied after the supply has been

powered up. In either case, the application of this load shall not cause the tracking

regulators to be permanently disabled.

VSB, VSC and VSD regulators can be disabled with VS_EN pin.

5.5 VKAM and VSTBY linear regulators

These two outputs are fully integrated low quiescent current low drop out regulators. The

input VBAT is used as the source of these supplies. These outputs are operational during

both standby and run mode; these are the only outputs operational during standby (V

BAT

not

present).

The VKAM regulator has two programmable levels: 1.0 V (VPROG1 pin connected to GND)

or 1.5 V (if this pin is left open, an internal pull-up is present).

The V

STBY

regulator has two programmable levels: 2.6 V (VPROG2 pin connected to GND)

or 3.3 V (if this pin is left open, an internal pull-up is present).

The STBY_OK pin indicates when the V

STBY

is out of range (voltage below the threshold

indicated in the electrical characteristic table). Once driven low it should stay low for a

minimal amount of time allowing external circuitry to latch.

DocID14273 Rev 5 23/30

L9758 Functional description

5.6 RESET monitors

RST5 is the reset signal tied to the V

DD5

supply. This is an open collector active low signal

that pulls low when V

DD5

is out of range.

RSTL is the reset signal for the V

DDL

supply. This is an open collector active low signal that

pulls low when V

DDL

is out of range. RST5 and RSTL are also driven low when STBY_OK

pin is driven low, regardless of the status of V

DD5

and V

DDL

Reset Delay is the time duration from when the output (V

DD5

or V

DDL

) is within range to

when the reset pin (RST5 or RSTL) is released. RST5 and RSTL use separate timers. This

delay is programmable via an external resistor connected to RST_TIM pin. A value of

4.7 kΩ corresponds to 1 ms and 47 kΩ to 10 ms. All values in between are linear

approximated. The timer delay is common however the attack and release times are only

dependant on the condition of the respective supplies (V

DD5

or V

DDL

5.7 Thermal protection

The tracking regulators incorporate thermal limit with shutdown. When the junction

temperature reaches the shutdown threshold, if there is a tracking regulator in current

limitation, it switches off and all the other regulators stay on. When the temperature

decreases the regulator restarts. The over temperature shutdown has a hysteresis to avoid

thermal pumping.

5.8 Reference current

The L9758 provides a DC voltage at the REXT pin. An external resistor to ground creates a

reference current which is mirrored internally for use in the device.

The reference current is used to supply all the analog blocks and to charge and discharge

an integrated capacitor to generate a 5 MHz clock for the switching functionality.

Figure 3. Current reference generator

The circuit is designed for a 10 kΩ resistor. For all affected parameters, this resistor value is

mentioned in the electrical characteristics section.

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Operating modes L9758

24/30 DocID14273 Rev 5

6 Operating modes

There are two modes of operation of the power supply: standby and run mode. However

during RUN mode, there are three input voltage regions: low voltage, normal voltage and

high voltage. A brief definition and description of each of these operating regions is

described below.

6.1 Standby mode

STANDBY mode is defined by the following conditions:

 VBAT is within the required voltage range

 VBAT_SW may or may not be present

 IGN is in the OFF state

 PSU_EN is not asserted by the microprocessor

During standby mode, all functions are shutdown except the two standby supplies, VKAM

and VSTBY, and the circuitry monitoring IGN and PSU_EN. During standby mode, current

consumption is minimized. The standby functions are powered from VBAT.

There is no currents drawn from VBAT_SW or any other input except those required to

perform the standby functions. Outputs, other than IGN_ON are disabled, sourcing nor

sinking current.

6.2 Run mode

RUN mode is defined by the following conditions:

 VBAT is within the required range

 VBAT_SW is within the required range

 Either IGN is in the Run state and/or PSU_EN is in the active state

During RUN mode, all functions can be enabled. All functions listed above, with the

exception of the standby functions, are powered by VBAT_SW.

If VBAT is not present, the circuit is fully running with the exception of PSU_EN and the

standby functions (VKAM and VSTBY). In this condition the entry into the RUN MODE can

only be performed by the IGN pin and the circuit is kept running until IGN pin is pulled low.

6.2.1 Entry into RUN mode

RUN mode is entered when at least one of the two signals IGN_SW or PSU_EN goes in the

active state. These two signals may be applied in any order or simultaneously.

When the IGN input is valid, the active low IGN_ON signal is asserted.

The design of VDD5, VDDL and VCORE regulators limits the slew rate of the output

voltages during the start-up as indicated in the electrical characteristic table and ensures

that V

DD5

is always greater than V

DDL

and V

CORE

As indicated in Figure 4, the switching regulator starts first with soft start control or reduced

current limitation. When the VB voltage reaches the VDDL_ENUP threshold all the linear

regulators start with controlled slew-rate. The slew-rate control is done controlling the slew

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L9758

Mfr. #:

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STMicroelectronics

Description:

Power Management Specialized - PMIC Multiple output Volt Reg Engine Ctrl

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L9758

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