IMP38C/HC/42/3/4/5
powered through the out pin. Leakage current from the external
power MOSFETs will not force the PWM output to rise and turn
the external MOSFETs on.
Current-sense propagation delay time is 35ns typical, 65ns maxi-
mum, representing an up to 75 percent reduction over other 38xx
implementations.
Output stage drive is 0.5A for IMP38C4x devices. The high-drive
IMP38HC4x family is rated at 1.0A peak current drive.
Like conventional 384x controllers, the IMP38C4x and
IMP38HC4x controllers use the current-mode architecture for
superior load regulation, pulse-by-pulse current limiting and out-
put MOSFET protection. All versions operate up to 20 volts.
For maximum application flexibility, start-up voltage ranges from
14.5V to 8.4V. Start-up current has been reduced to 120µA maxi-
mum and operating current has been reduced to 1.5mA maximum.
The IMP38C4x/IMP38HC4x are available in 8-pin and 14-pin DIP
and SO packages as well as the 8-pin MicroSO package. The 14-
pin devices provide separate pins for the controller power supply
and the output driver supply. This configuration maximizes
application flexibility and performance. The 14-pin package can
also dissipate more power. Devices in the compact 8-pin packages
do not have separate output drive supply connections.
The IMP38C4x and IMP38HC4x families operate over the –40°C
to +85°C temperature range.
Pin Configuration
SO/MicroSO/DIP
COMP 1
FB 2
ISNS 3
RT/CT 4
IMP38C4x
IMP38HC4x
8 V
REF
7 V
DD
6 OUT
5 GND
38C/HC_02.eps
SO/DIP
COMP 1
NC 2
FB 3
NC 4
ISNS 5
NC 6
RT/CT 7
14 V
REF
13 NC
IMP38C4x
12 V
DD
IMP38HC4x
11 V
D
10 OUT
9 AGND
8 PGND
38C/HC_03.eps
Pin Descriptions
Pin Number
8-Pin Package
1
2
3
4
14-Pin Package
1
3
5
7
Name
COMP
FB
ISNS
RT/CT
Function
Output of the Error amplifier and input to the PWM comparator.
Inverting input of the Error Amplifier.
Current sense comparator input. It is internally limited to 1V.
Oscillator RC timing component connection. Resistor RT is connected to
V
REF
and capacitor CT is connected to ground. Different values of RT and
CT determine the maximum duty cycle.
Combined power and analog ground for 8-pin packaged devices and power
ground for 14-pin package.
High-power, totem-pole driver output. OUT pin is actively held LOW when
V
CC
is below the UVLO threshold.
Supply voltage input.
5V-reference voltage output.
Analog ground connection for 14-pin package.
Output driver supply voltage for 14-pin package.
No internal connection.
38C-HC_t01.eps
5
6
7
8
8
10
12
14
9
11
2, 4, 6, 13
GND/PGND
OUT
V
DD
V
REF
AGND
V
D
NC
2
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© 2000 IMP, Inc.
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IMP [ IMP, INC ]
