Application Information
The CS452/453 is provided with an input lead (VIN) which
Input
turns the injector driver ÓonÒ and ÓoffÒ. This lead has a
nominal trip level of 1.4V and an input impedance of
20k½. It is internally protected against negative voltages
and is compatible with TTL and most other logic.
>1.4V
>1.5V
Signal
V
IN
Control
There is also a control lead (CONTROL) which if held low
or grounded, permits the device to operate in saturation to
Ipk(sense), where it will switch to Isus automatically. If CON-
TROL is brought high (>1.5V), the output drive stage is
turned off, regardless of what state the input (VIN) is at,
and the output current goes to zero.
Signal
CONTROL
Ipk
Output
Current
Isus
tl
Figure 1 shows the operating waveforms for the simplest
mode; i.e., with CONTROL grounded. When the driver is
turned on, the current ramps up to the peak current sense
level, where some overshoot occurs because of internal
delay. The CS452/453 then reduces its output to Isus. The
fall time of the device is very rapid (²1.0µs), but the decay
of the load current takes 150 to 220 µs, while dumping the
load energy into the protection Zener clamp.
Figure 4. Application of CONTROL
Provided in Figures 2,3, and 4 are definitions of the
switching intervals specified in the Electrical
Characteristics. Figure 3 shows that the critical switching
parameters stay under control at elevated temperatures.
In those applications where high voltage transients may
occur while the output lead (OUT) is in the Isus mode,
excessive instantaneous power dissipation may occur,
causing device failure. When this condition occurs, the
control lead (CONTROL) can be used to shut off the out-
put stage in order to protect the CS452/453. As long as
CONTROL is in the high state (>1.5 volts, typ.), the output
will remain off. One method of sensing the supply voltage
and controlling CONTROL is to use a resistor divider
between the supply voltage and ground with CONTROL
connected to the resistor divider (see Typical Application
diagram).
It is essential that the Zener voltage be lower than the
V(BR)CEO(sus), but not so low as to greatly stretch the load
current decay time. Without the zener, the discharge of the
load energy would be totally into the CS452/453, which, for
the high current applications, could cause the device to fail.
Also in figure 1 is the graphically derived instantaneous
power dissipation of the CS452/453. It shows that, for
practical purposes, the worst case dissipation is less than
(Isus) (VBAT) (duty cycle).
Another application option of the control lead is to use it
to accomplish an enable/disable function. Since CON-
TROL is compatible with TTL and CMOS logic levels, a
logic low will enable the output, and allow it to follow the
input signal at VIN. If CONTROL is held at a logic high,
the output will be disabled regardless of the state of the
input signal.
Ipk
90%
Output
Output
Current
Vl Turn
Off
Voltage
10%
0
ts
If the control function is not being used in the application,
it must be grounded or otherwise placed in a logic low
state. If CONTROL is left open, the output stage will
remain off.
tv tf
0
1.0
2.0
3.0 ms
Figure 2. Switching Waveforms (Expanded Time Scale)
The output current in the Isus mode should be oscillation
free. There is a possibility that in a given application, the
output current could oscillate for a small fraction of parts.
If this was to occur, the remedy is place a capacitor from
OUT to Ground. The value of the capacitor should not
exceed 0.01µF.
2.0
ts
1.5
1.0
0.5
0
tf
tv
-40 -20
0
20 40 60 80 100 120 140
Case Temperature (ûC)
Figure3. Switching Speed vs. Temperature
4
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
