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PDF GM3843A Datasheet ( Hoja de datos )

Número de pieza GM3843A
Descripción (GM3842A - GM3845A) HIGH PERFORMANCE CURRENT MODE PWM CONTROLLERS
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GM3843A datasheet

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GM3843A pdf
ELECTRICAL CHARACTERISTICS
(TA = 0°C to 70°C, *VCC=15V, CT=3.3nF, RT=10kW, unless otherwise specified )
CHARACTERISTICS
SYMBOL
Reference Section
Reference Output Voltage
Line Regulation
Load Regulation
Short Circuit Output Current
Oscillator Section
Oscillation Frequency
Frequency Change with Voltage
Oscillator Amplitude
Error Amplifier Section
Input Bias Current
Input Voltage
Open Loop Voltage Gain
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
High Output Voltage
Low Output Voltage
Current Sense Section
Current Sense Input Voltage Gain
Maximum Input Signal
Supply Voltage Rejection
Input Bias Current
Output Section
VREF
DVREF
DVREF
ISC
f
Df/ DVCC
V(OSC)
IBIAS
VI(EA)
AVOL
PSRR
ISINK
ISOURCE
VOH
VOL
GV
VI(MAX)
SVR
IBIAS
Low Output Voltage
VOL
High Output Voltage
VOH
Rise Time
Fall Time
Undervoltage Lockout Section
tR
tF
Start Threshold
VTH(ST)
Minimum Operating Voltage
(after tum ON)
VOPR(MIN)
TEST CONDITIONS
TJ= 25°C, IREF= 1mA
12V VCC 25V
1mA IREF 20mA
TA=25°C
TJ= 25°C
12V VCC 25V
(Peak to Peak)
VFB= 3V
VPIN1=2.5V
2V VO 4V
12V VCC 25V
VPIN2=2.7V, VPIN1=1.1V
VPIN2=2.3V, VPIN1=5V
VPIN2=2.3V, RL=15kW to GND
VPIN2=2.7V, RL=15kW to PIN8
(Note 1 and 2)
VPIN1=5V (Note 1)
12V VCC 25V (Note 1)
VPIN3=3V
ISINK= 20mA
ISINK= 200mA
ISOURCE= 20mA
ISOURCE= 200mA
TJ= 25°C, CL= 1nF(Note 3)
TJ= 25°C, CL= 1nF(Note 3)
GM3842A, GM3844A
GM3843A, GM3845A
GM3842A, GM3844A
GM3843A, GM3845A
MIN
4.9
47
2.42
65
60
2
-0.5
5.0
2.85
0.9
13
12
14.5
7.8
8.5
7.0
TYP MAX UNIT
5.0
6.0
6.0
-100
52
0.05
1.6
-0.1
2.5
90
70
7
-1.0
6.0
0.8
3.0
1.0
70
-3.0
0.08
1.4
13.5
13
45
35
16.0
8.4
10
7.6
5.1
20
25
-180
57
1.0
-2
2.58
1.1
3.15
1.1
-10
0.4
2.2
150
150
17.5
9.0
11.5
8.2
V
mV
mV
mA
kHz
%
V
µA
V
dB
dB
mA
mA
V
V
V/ V
V
dB
µA
V
V
nS
nS
V
V
5

5 Page

GM3843A arduino
Current mode converters can exhibit subharmonic oscillations when operating at a duty cycle greater than 50%
with continuous inductor current. This instability is independent of the regulators closed–loop characteristics and
is caused by the simultaneous operating conditions of fixed frequency and peak current detecting. Figure 9.A
shows the phenomenon graphically. At t0, switch conduction begins and causes causing the inductor current to
rise at a slope of m1. This slope is a function of the input voltage divided by the inductance. At t1, the Current
Sense Input
reaches the threshold established by the control voltage.
This causes the switch to turn off and the current to decay at a slope of m2 until the next oscillator cycle. The
unstable condition can be shown if a pertubation is added to the control voltage, and resulting in a small DI
(dashed line). With a fixed oscillator period, the current decay time is reduced and the minimum current at switch
turn–on (t2) is increased by DI + DI m2/m1. The minimum current at next cycle (t3) decreases to (DI + DI m2/m1)
(m2/m1). This pertubation is multiplied by m2.m1 on each succeeding cycle, alternately increasing and decreasing
the inductor current at switch turn–on. Several oscillator cycles may be required before the inductor current
reaches zero, which caused causing the process to commence again. If m2/m1 is greater than 1, the converter
will be unstable. Figure 9.B shows that by adding an artificial ramp, that is synchronized with the PWM clock to
the control voltage, the DI pertubation will decrease to zero on succeeding cycles. This compensation ramp (m3)
must have a slope equal to or slightly greater than m2/2 for stability. With m2/2 slope compensation, the average
inductor current follows the control voltage yielding true current mode operation. The compensating ramp can be
Control Voltage
DI
Inductor
Current
m1
DI + DI
m2
m2
m1
Oscillator Period
t0 t1
A
(DI
+
DI
m2
m1
)
(
mm21)
t2
t3
Control Voltage
m3
B
DI
t4
m1
m2
Oscillator Period
t5
Inductor
Current
t6
Figure 9. Continuous Current Waveforms
10

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