NCV7721
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9
DETAILED OPERATING DESCRIPTION
General
The NCV7721 Dual Half Bridge Driver provides drive
capability for 2 Half−Bridge configurations. Each output
drive is characterized for a 500 mA load with capability up
to 1.1 A (min overvoltage shutdown threshold). Strict
adherence to the integrated circuit die temperature is
necessary, with a maximum die temperature of 150°C.
Output drive control is handled via the parallel input control
pins (IN1 & IN2). A single open Drain output reports
underload, overload, and thermal shutdown faults.
An Enable function (EN) provides a low quiescent sleep
current mode when the device is not being utilized. A
resistor pulldown is provided on EN, IN1, and IN2 to insure
a predictive state (low) in the event of a detached input
signal.
Power Up/Down Control (Undervoltage Detection)
A feature incorporated in the NCV7721 is an
undervoltage lockout circuit that prevents the output drivers
from turning on unintentionally. VCC and V
S
are monitored
for undervoltage conditions supporting a smooth turn−on
transition. All drivers are initialized in the off (high
impedance) condition, and will remain off during a VCC or
V
S
undervoltage condition. This allows power up
sequencing of VCC and V
S
up to the user. Hysteresis in the
UVLO circuits results in glitch free operation during power
up/down.
Overvoltage Shutdown
Overvoltage lockout monitors the voltage on the V
S
pin.
When the overvoltage voltage threshold is breached (36.5 V
[typ]), all outputs will turn off and remain off until V
S
is out
of overvoltage. A typical voltage hysteresis of 2.5 V
eliminates the possibility of oscillation at the shutdown
threshold.
H−Bridge Driver Configuration
The NCV7721has the flexibility of controlling each half
bridge driver independently through the IN1 and IN2 logic
input pins. This allows for high−side, low side and H−Bridge
control. H−bridge control provides forward, reverse, brake
and high impendence states.
Overvoltage Clamping – Driving Inductive Loads
Each output is internally clamped to ground and V
S
by
internal freewheeling diodes. The diodes have ratings that
complement the FETs they protect. A flyback event from
driving an inductive load causes the voltage on the output to
rise up. Once the voltage rises higher than V
S
by a diode
voltage (body diode of the high−side driver), the energy in
the inductor will dissipate through the diode to V
S
. If a
reverse battery diode is used in the system, care must be
taken to insure the power supply capacitor is sufficient to
dampen any increase in voltage to V
S
caused by the current
flow through the body diode so that it is below 40 V.
Negative transients will momentarily occur when a
high−side driver driving an inductive load is turned off. This
will be clamped by an internal diode from the output pin
(OUT1 or OUT2) to the IC ground.
Current Limit
OUTx current is limited per the Current Limit electrical
parameter for each driver. The magnitude of the current has
a minimum specification of 2 A at VCC = 5 V and V
S
=
13.2 V. The output is protected for high power conditions
during Current Limit by thermal shutdown and the
Overcurent Detection shutdown function. Overcurrent
Detection shutdown protects the device during current limit
because the Overcurrent threshold is below the Current
Limit threshold. The Over current Detection Shutdown
Control Timer is initiated at the Overcurrent Shutdown
Threshold which starts before the Current Limit is reached.
Note: High currents will cause a rise in die temperature.
Devices will not be allowed to turn on if the die temperature
exceeds the thermal shutdown temperature.
Overcurrent Shutdown
Effected outputs will turn off when the Overcurrent
Shutdown Threshold has been breached for the Overcurrent
Shutdown Delay Time. FLTB will report a low and the
driver will latch off. The driver can only be turned back on
by a toggle of the EN pin or a power on reset of VCC.
Overcurrent Detection Shut Down Timer
There are two protection mechanisms for output current,
overcurrent and current limit.
1. Current Limit – Maximum current for OUT1 and
OUT2.
2. Overcurrent Detection – Threshold at which timer
starts.
Figure 8 shows the typical performance of a part which
has exceeded the 1.45 A (typ) Overcurrent Detection
threshold and started the shutdown timer.
1.45 A
25 usec
Figure 8. Output Current Shutdown Control
