SPSB100 datasheet(14/213 Pages) STMICROELECTRONICS

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3.2

Boost controller

The boost, or step up controller, generates an output voltage that supplies the SPSB100 device and the BUCK

converters, only during a transitory time at power up to reach a normal operating range (12 V battery range), or

only during low battery conditions for a transitory time, or for sustaining deep cranking.

In case the VS voltage exceeds the VTH_BYPASS threshold, the converter is deactivated and battery supplies, via

separate bypass MOSFET, the BUCK converters. The live bit BOOST_ENA_STATUS reflects the state of the

boost.

The block diagram of the boost is shown in the figure below.

Figure 7. Boost controller block diagram

L_Boost

Logic

GLB

Boost

Driver

Stage

FBB

Vth

Boost_En

PWM

Duty Cycle Control

Rg_pd

AND

Enable

Vbat

D1_Boost

Q1_Boost

C_Boost

Output voltage sense

V_Boost

Q2_Bypass

GBY

Bypass Driver

V compth1

V compth2

V compth3

Rpr

D2_Boost

DZby

Rcl

CVBAT

DLB

According to the sensed battery voltage on VS pin (VS_LOW, VS_MID and VS_HIGH thresholds), the boost duty

cycle is suitably adjusted ( BOOST_DC_Max when VS voltage is between VS_POR and VS_LOW,

BOOST_DC_High when VS is between VS_LOW and VS_MID, BOOST_DC_Mid when VS is between VS_MID and

VS_HIGH and BOOST_DC_Low when VS is higher than VS_HIGH) to keep the output voltage quite over the

selected thresholds (VFBB_REG1 or VFBB_REG2, automatically set by state machine and readable by status register

bit BOOST_LEVEL_SET).

The system is compliant to the new defined “cold cranking pulse” required by start-stop systems. Moreover, a

suitable bypass MOSFET is driven when the BOOST is not switching to bypass the inductor, minimizing the

overall losses during normal operation.

The boost and the bypass drivers can be switched permanently OFF by setting respectively BOOST_DIS = 1 and

BYPASS_DIS = 1 in the USER-NVM space.

If the BOOST function is used (BOOST_DIS = 0):

•

At power-up, the bypass control is enabled when the state machine enters in INIT state (after successful

safety checks). If VS > VTH_BYPASS_R, the external bypass switch is turned on (BYPASS_STATUS = 1)

while the boost pwm is forced low. When VS < VTH_BYPASS_F, the external switch is turned off

(BYPASS_STATUS = 0) and the boost switching is activated.

•

In ACTIVE–FULL-POWER mode and in RECOVERY-1 state, when VS > VTH_BYPASS_R, the external

bypass switch is turned on after tF_BYPASS_EN timing (BYPASS_STATUS = 1) and the boost pwm is forced

low if FBB > FBB_REG1 (or FBB_REG2) threshold. When VS < VTH_BYPASS_F, the bypass switch is turned

off after tF_BYPASS_DIS timing (BYPASS_STATUS = 0) and the boost switching is activated if FBB <

FBB_REG1 (or FBB_REG2) threshold.

•

In ACTIVE–LOW-POWER mode, the BYPASS controller is disabled, turning off the external switch

(BYPASS_STATUS = 0): the consumption on the battery is limited to a few mAmps so no dissipation issue

is expected in the external diode.

•

In ACTIVE–LOW-POWER mode, the BOOST IP is disabled to reduce the overall SPSB100 consumption. It

is woken up when the monitored VFBB becomes close to the minimum operating supply (FBB_OK_LP_F1

or FBB_OK_LP_F2) for the remaining active BUCK with duty cycle BOOST_DC_LP.

•

In RECOVERY-2 or DEEP-SLEEP state, the boost is always OFF and the BYPASS controller is always

disabled (BYPASS_STATUS = 0).

SPSB100

Functional description

DS14640 - Rev 2

page 14/213

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