ABSOLUTE MAXIMUM RATINGS

Symbol

Parameter

Value

Max Forward Voltage
Positive Transient Peak Voltage (dump :

fall time constant = 100ms,

5ms

rise

10ms, R

source

0.5

)

Resistive Load
Inductive Load

50Vdc

60V

50V (*)

Reverse Input Voltage

0.3Vdc

Input Voltage Pin 2 (to GND)
Pin 4 Voltage
Pin 5 Voltage
(to GND)
(to GND)

0.3V / + V

< 20V)

0.3V / + V

< 20V)

3V / + V

< 20V)

Pin 1 Current
Pin 2 Current (forced)
Pin 4 Current (sink)
Pin 5 Current

Internally Limited

0.5mA

10mA

Internally Limited

TOT

Power Dissipation

Internally Limited

, T

STG

Junction and Storage Temperature Range

C to + 150

due to the negative voltage at the output during the switching off.

THERMAL DATA

Symbol

Parameter

Value

Unit

th j-case

Thermal Resistance Junction-case

Max

1.5

C/W

PIN CONNECTION (top view)

L9821

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PIN FUNCTIONS

1. POWER SUPPLY

Supply voltage input. When the supply reaches the
maximum operating voltage (32V) the device is tur-
ned off, protecting itself and the load.
Turning off guaranteed for V

> 41V.

2. INPUT

TTL compatible input. High level on this pin means
outputcurrentON. Thelow level voltageswitches off
the charge pump, the power stage and the diagno-
stic output reducing to the minimum value the quie-
scent current.

3. GROUND

This pin must be connected to ground.

4. DIAGNOSTIC FEEDBACK
The diagnostic circuit is active in input high level

condition. This output detects with Tipically 45ms
delay at T

amb

= 25

C the following faults :

Overvoltage condition.

Thermal shutdown.

Short circuit. The power stagecurrent is internally
limited at 25A.

Open load. The open load condition is detected
with load current < 0.6A.

The diagnostic output is active low. The diagnostic
delay time allows to avoid spurious diagnosys (i.e :
turn ON overcurrent, overvoltage spikes etc.).

5. POWER OUTPUT

The device is provided with short circuit protection
at Vs

14.4V

ELECTRICAL CHARACTERISTICS (V

= 14.4V; -40

125

C, unless otherwise specified)

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

Operat. Voltage

On Resistance

Input >2V:T

= 25

Input >2V:Full T range

0.1

0.2

Short circuit current

Over Current Detection Level

OPD

Open Load Detection Level

Device ON

1.2

clamp

Output Under Voltage Clamping

load

<6A Inductive

-12

-4

Off

Off State Supply Current

= -40 to 35

= 35 to 85

100
300

ON State Supply Current

= 25

Input Low Level

0.8

Input High Level

2.0

Input Current

= V

th reshold

LEAKD

Diagnostic Output Leakage
Voltage

VCC = 5V
Diagnostic Output

SATD

Diagnostic Output Saturation
Voltage

sink

<1.6mA

0.4

Diagnostic Delay Time

= 25

dON

Output ON Delay Time

= 25

Output ON Rise Time

= 25

dOFF

Output OFF Delay Time

= 25

Output OFF Fall Time

= 25

100

L9821

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FUNCTIONAL DESCRIPTION

The L9821is a high sidedrive monolithic switch, dri-
ven by TTL, CMOS input logic, able to supply resi-
stive or inductive loads up to 6A DC allowing a
current peak of 25A with a R

DS(ON)

= 0.1. The elec-

tronicswitch, in additionto its main function,protects
itself, the power network and the load against load
dump (up to 60V) and overload and it detects short
circuit, open load and overtemperature conditions.
All these functions (logic control and power actua-
tion) are possible on a singlechip thanks to the new
mixed ST MultipowerBCD technologythat allows to
integrate isolated DMOS power transistors in com-
binationwith Bipolarand CMOS signal structureson
the same chip.

The high side drive connection (series switch bet-
ween the load and the positive power source)is par-
ticularlysuited in automotiveenvironmentwherethe
electrochemical corrosion withstandinghas primary
importance. For this connection the best solution is
a Power MOS N-channel which requires for driving
only a capacitive charge pump completely integra-
ted on the switch chip.

The L9821 is based on a power DMOS series ele-
ment, a driving circuit with a charge pump, an input
logic interface and on some protection and fault de-
tection circuits.

The power DMOS transistor has a R

DS(ON)

= 0.1

(typ. value @ T

= 25

C, V

= 10V). The low value

of R

DS(ON)

is important both to increase the power

transferred to the load and to minimize the power
dissipated in the device.

The charge pump is a capacitivevoltage tripler star-
ting from power supply (car battery), driven by a
500kHz oscillator.

The input interface is based on a circuitry solution
able to guarantee the stability over temperature of
the TTL logic levels and very low quiescent current
in OFF condition.

When the supply reaches the maximum operating
voltage (32V) the device is turned OFF, protecting
itself and the load ; moreoverlocal zener clamps are
provided in some critical points to avoid that V

any MOS transistor could reach dangerous values
even during 60V load dump transient.

The inrush current limiting is a significant feature of
the L9821. This functionallows to protect the power
supply network and may extend the life of the loads.
For example, in the case of the lamps, the tungsten
wire resistance value in cold condition is about one
tenth of the nominal steadystate and then the inrush
current during the turn on is statistically one of the
main causes of lamps failures. If the high current
condition persists (e.g. load short circuit) and the
junctiontemperaturerises above150

C,the thermal

protection circuit turns off the device preventingany
damage. The current limiting and the thermal shut-
down are sufficient to protectthe device againstany
overload becausethe power DMOS has not the se-
cond breakdown.

When the L9821 is driven and one of the protec-
tions (overtemperature, overvoltage, overload) is
present, a fault detection open drain output turns
on. This output is active also when I

load

is lower

than 0.6A detecting the open load (disconnected or
burned out). The diagnostic output detects fault
conditions with 25ms delay in order to avoid spu-
rious diagnosys (i.e. : turn on overcurrent, overvol-
tage spikes etc.). In OFF conditions the fault
detection circuits are not active to allow a minimum
quiescent current.

The device can drive unipolar DC motors and sole-
noids as well becauseit can recirculate an inductive
current when the output voltage goes lower than
V

clamp

value (typically - 6.5V in respect to ground).

The possibility to have a start up current is useful
also for DC motors allowing the maximum starting
torque.

TYPICAL APPLICATION OF THE L9821

The L9821 integrated high side driver can be used
to replace an electromechanical relay.

Inductiveload (i.e. solenoids,motors) can be driven
by the L9821. No externalcomponents are required
for the coil current recirculation, because the device
provides this function internally.

L9821

4/7

Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for
the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its
use. No license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specification
mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously
supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems
without express written approval of SGS-THOMSON Microelectronics.

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L9821

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