Control input for the Pulse Width Modulator COMP pull-up is provided by an internal 5K resistor
and Hiccup comparators.
which may be used to bias an opto-coupler transistor.
Input voltage.
Output of a linear bias supply regulator.
Nominally 8.5V.
MOSFET gate driver output.
Input to start-up regulator. The VIN pin is clamped at
36V by an internal zener diode.
VCC provides bias to controller and gate drive sections
of the LM5021. An external capacitor must be connected
from this pin to ground.
High current output to the external MOSFET gate input
with source/sink current capability of 0.3A and 0.7A
respectively.
Current sense input for current mode control and
over-current protection. Current limiting is accomplished
using a dedicated current sense comparator. If the CS
comparator input exceeds 0.5 Volts the OUT pin
switches low for cycle-by-cycle current limit. CS is held
low for 90ns after OUT switches high to blank the
leading edge current spike.
An external resistor connected from RT to GND sets the
oscillator frequency. This pin will also accept
synchronization pulses from an external clock.
An external capacitor and an internal 22 µA current
source set the soft-start ramp. The soft -start capacitor
controls both the soft-start rate and the hiccup mode
period.
4
OUT
5
6
GND
CS
Ground return.
Current Sense input.
7
RT / SYNC Oscillator timing resistor pin and
synchronization input.
SS
Soft-start / Hiccup time
8
www.national.com
2
LM5021
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN to GND
VIN Clamp Continuous Current
CS to GND
RT to GND
All other pins to GND
-0.3V to 30V
5mA
-0.3V to 1.25V
-0.3V to 5.5V
-0.3V to 7.0V
ESD Rating (Note 2)
Human Body Model
Storage Temperature
Operating Junction Temperature
2kV
-65˚C to +150˚C
+150˚C
Operating Ratings
(Note 1)
VIN Voltage (Note 5)
Junction Temperature
8V to 30V
-40˚C to +125˚C
Specifications in standard type face are for T
J
= +25˚C and those in
boldface
type
apply over the full
Operating Junction Temperature Range.
Unless otherwise specified: V
IN
= 15V, R
T
= 44.2KΩ.
(Note 3)
Symbol
STARTUP CIRCUIT
Start Up Current
VCC Regulator enable threshold
VCC Regulator disable
threshold
VIN ESD Clamp voltage
I
VIN
Operating supply current
Controller enable threshold
Controller disable threshold
VCC regulated output
VCC dropout voltage (VIN -
VCC)
VCC regulator current limit
SKIP CYCLE MODE COMPARATOR
Skip Cycle mode enable
threshold
Skip Cycle mode hysteresis
CURRENT LIMIT
CS limit to OUT delay
CS stepped from 0
to 0.6V, time to OUT
transition low, C
load
= 0.
0.45
35
ns
13
Electrical Characteristics
Parameter
Conditions
Before VCC Enable
Min
Typ
18
Max
25
23
Unit
µA
V
V
17
20
7.25
I = 5mA
COMP = 0VDC
30
36
2.5
40
3.75
7.5
6.3
9
V
mA
V
V
V
V
mA
VCC SUPPLY
6.5
5.3
No External Load
I = 5 mA
VCC = 7.5V (Note
4)
⁄ [COMP - 1.25V]
15
8
7
5.8
8.5
1.7
22
75
125
5
175
mV
mV
CS limit threshold
Leading Edge Blanking time
CS blanking sinking impedance
SOFT-START
V
SS-OCV
SS pin open-circuit voltage
Soft-start Current Source
Soft-start to COMP Offset
COMP sinking impedance
OSCILLATOR
Frequency1 (RT = 44.2K)
Frequency2 (RT = 13.3K)
Sync threshold
During SS ramp
0.5
90
35
0.55
55
6.1
30
0.75
V
ns
Ω
V
µA
V
Ω
4.3
15
0.35
5.2
22
0.55
60
135
440
2.4
150
500
3.2
165
560
3.8
kHz
kHz
V
3
www.national.com
LM5021
Electrical Characteristics
Specifications in standard type face are for T
J
= +25˚C and those in
boldface type
apply over the full
Operating Junction Temperature Range.
Unless otherwise specified: V
IN
= 15V, R
T
= 44.2KΩ. (Note
3) (Continued)
Symbol
PWM COMPARATOR
COMP to OUT delay
COMP set to 2V
CS stepped 0 to
0.4V, time to OUT
transition low, C
load
= 0.
COMP = 0V
75
80
50
0.33
4.2
COMP = 0V
CS pin to PWM
Comparator offset at
maximum duty cycle
IOUT = 50mA, VCC
- OUT
IOUT = 100mA
OUT = VCC/2.
OUT = VCC/2.
C
load
= 1nF
C
load
= 1nF
COMP pin
SS pin
SS pin
0.6
70
5.1
2.75
1.1
90
1.5
110
6
V
V
mA
mV
20
ns
Parameter
Conditions
Min
Typ
Max
Unit
Min Duty Cycle
Max Duty Cycle (-1 Device)
Max Duty Cycle (-2 Device)
COMP to PWM comparator gain
COMP Open Circuit Voltage
COMP at Max Duty Cycle
COMP Short Circuit Current
SLOPE COMPENSATION
Slope Comp Amplitude
(LM5021-1 only)
OUTPUT SECTION
OUT High Saturation
OUT Low Saturation
Peak Source Current
Peak Sink Current
Rise time
Fall time
HICCUP MODE
V
OVLD
V
HIC
V
RST
I
DTCS
I
OVCS
Over load detection threshold
Hiccup mode threshold
Hiccup mode Restart threshold
Dead-time current source
Overload detection timer current
source
MSOP-8 Junction to Ambient
MDIP-8 Junction to Ambient
0
85
%
%
%
0.6
0.3
0.3
0.7
25
10
1.1
1
V
V
A
A
ns
ns
V
V
V
µA
µA
V
SS-OCV
– 0.8
V
SS-OCV
– 0.6
V
SS-OCV
– 0.4
V
SS-OCV
– 0.8
V
SS-OCV
– 0.6
V
SS-OCV
– 0.4
0.1
0.1
6
0.3
0.25
10
0.5
0.4
14
THERMAL RESISTANCE
θ
JA
θ
JA
0 LFM
0 LFM
200
107
˚C/W
˚C/W
Note 1:
Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device
is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2:
The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3:
Min and Max limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical
Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL).
Note 4:
Device thermal limitations may limit usable range.
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