The device is activated with enable input voltage
HIGH. For enable input floating (not connected)
or LOW the device is in Standby Mode. Very low
quiescent current is defined for V
EN
< 0.3V. When
activating or disactivating the device by the en-
able input a wake-up time of 50
µ
s is recom-
mended.
For braking of the motor the status 2 is recom-
mended. The reason for this recommendation is
that the device features higher threshold for ini-
tialisation of parasitic structures than in state 5.
The inputs IN1, IN2 features internal sink current
generators of 10
µ
A, disabled in standby mode.
With these input current generators the input level
is forced to LOW for inputs open. In this condition
the outputs are in SNK state.
The circuit features an overvoltage disable func-
tion referred to the supply voltage V
VS
. This func-
tion assures disabling the power outputs, when
the supply voltage exceeds the over voltage
threshold value of 19V typ. Both outputs are
forced to tristate in this condition and the diagnos-
tic output is ON.
The thermal shut-down disables the outputs (tris-
tate) and activates the diagnostic when the junc-
tion temperature increases above the thermal
shut-down threshold temperature of min. 150°C.
For the start of a heavy loaded motor, if the motor
current reaches the max. value, it is necessary to
respect the dynamical thermal resistance junction
to ambient. The outputs OUT1 and OUT2 are pro-
tected against short circuit to GND or V
S
, for sup-
ply voltages up to the overvoltage disable thresh-
old.
The output power DMOS transistors works in lin-
ear mode for an output current less than 1.2A. In-
creasing the output load current (> 1.2A) the out-
put transistor changes in the current regulation
mode, see Fig.6, with the typical output current
value below 2A. The SRC output power DMOS
transistors requires a voltage drop ~3V to activate
the current regulation. Below this voltage drop is
the device also protected. The output current heat
up the power DMOS transistor, the R
DSON
in-
creases with the junction temperature and de-
creases the output current. The power dissipation
in this condition can activate the thermal shut-
down . In the case of output disable due to ther-
mal overload the output remains disabled untill
the junction temperature decreases under the
thermal enable threshold.
Permanent short circuit condition with power dis-
sipation leading to chip overheating and activation
of the thermal shut-down leads to the thermal os-
cillation. The junction temperature difference be-
tween the switch ON and OFF points is the ther-
mal hysteresis of the thermal protection. This
hysteresis together with the thermal impedance
and ambient temperature determines the fre-
quency of this thermal oscillation, its typical val-
ues are in the range of 10kHz.
The open drain diagnostic output needs an exter-
nal pull-up resistor to a 5V supply. In systems
with several L9997ND the diagnostic outputs can
be connected together with a common pull-up re-
sistor. The DIAG output current is internally lim-
ited.
Fig. 1 shows a typical application diagram for the
DC motor driving. To assure the safety of the cir-
cuit in the reverse battery condition a reverse pro-
tection diode D
1
is necessary. The transient pro-
tection diode D
2
must assure that the maximal
supply voltage V
VS
during the transients at the
V
BAT
line will be limited to a value lower than the
absolute maximum rating for V
VS
.
M
V
S
5V
C
S
IN1
IN2
GND
DIAG1
CONTROL
LOGIC
47K
Ω
IDIAG1
IIN1
IIN2
IEN
EN
D
2
V
BAT
D
1
I
s
L9997ND
OUT1
IM
VM
IOUT1
IOUT2
OUT2
GND
Figure 1:
Application Circuit Diagram.
L9997ND
4/9
