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NCS29001DR2G

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
NCS29001
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13
SIZING THE R
comp
RESISTOR for the LOOP STABILITY
Combining Equations 2 and 16 gives the following expression for I
OUT
:
I
OUT
+
V
f
2
L F
sw
2
ǒ
V
OUT
* V
IN
Ǔ
ǒ
R
CS
G
i
Ǔ
2
(eq. 20)
To obtain the small signal equation, partial derivates of the output current are calculated with respect to the control voltage Vc
and the output voltage V
OUT
.
I
OUT
V
OUT
+
V
C
L F
sw
ǒ
V
OUT
* V
IN
Ǔ
ǒ
R
CS
G
i
Ǔ
2
∂
∂
(eq. 21)
I
OUT
V
OUT
+
V
C
2
L F
sw
2
ǒ
V
OUT
* V
IN
Ǔ
2
ǒ
R
CS
G
i
Ǔ
2
+
I
OUT
V
OUT
* V
IN
∂
∂
(eq. 22)
From the AC model below the control to output transfer function can be calculated:
Figure 8. Control to Output Transfer Function
H(s) +
V
OUT
(s)
V
C
(s)
+
V
OUT
(s)
I
(s)
I
OUT
(s)
V
C
(s)
(eq. 23)
H(s) + Z
OUT
(s)
I
OUT
(s)
V
C
(s)
(eq. 24)
Z
OUT
(s) +
ǒ
ESR )
1
sC
OUT
Ǔ
R
eq
ǒ
ESR )
1
sC
OUT
Ǔ
) R
eq
+ R
eq
1 ) s ESR C
OUT
1 ) s C
OUT
ǒ
ESR ) R
eq
Ǔ
(eq. 25)
Where
R
eq
+
R
ac
R
1
R
ac
R
1
R
1
+
1
I
OUT
(s)
V
OUT
(s)
+
2
ǒ
V
OUT
* V
IN
Ǔ
2
ǒ
R
cs
G
i
Ǔ
2
V
c
2
F
sw
L
+
V
OUT
* V
IN
I
OUT
(eq. 26)
The dynamic resistance r
AC(LED)
is evaluated using the LED specification.
R
AC
+ R
sense
) r
AC(LED)
nb
LED
(eq. 27)
NCS29001
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14
Theory
The control to output transfer function is expressed following the formula below:
H(s) + H
0
1 )
s
w
z
1 )
s
s
p
(eq. 28)
Where
H
o
+
I
OUT
V
C
R
eq
+
V
C
L F
sw
ǒ
V
OUT
* V
IN
Ǔ
ǒ
R
CS
G
I
Ǔ
2
R
AC
R
1
R
AC
) R
1
∂
∂
(eq. 29)
H
o
+
2 I
OUT
L F
sw
ǒ
V
OUT
* V
IN
Ǔ
Ǹ
1
R
CS
G
i
R
AC
R
1
R
AC
) R
1
(eq. 30)
f
p
+
1
2p
ǒ
ESR ) R
eq
Ǔ
C
OUT
(eq. 31)
There is also a right half plane zero:
f
z
+
1
2p ESR C
OUT
(eq. 32)
As the boost converter also operates in DCM, there is also a right half plane zero regulated to high frequency:
f
rhpz
+
2 f
sw
2p D
(eq. 33)
Type II compensation is used to compensate the two dominant poles f
p
of the control to output transfer function.
The compensator zero has to be placer at the f
p
frequency of the transfer function.
f
p
+
1
2p (ESR ) R
eq
) C
OUT
+ f
z
+
1
2p R
comp
C
comp
(eq. 34)
R
comp
+
(ESR ) R
eq
) C
OUT
C
comp
(eq. 35)
The dominant pole is expressed following the equation:
f
p1
+
1
2p R
EA
C
comp
(eq. 36)
Figure 9. Slope Compensation Network
gm
+
−
COMP
Type II
Compensation
Ccomp2
Ccomp
Rcomp
C
bw =
C
pad+Comp2
Cpad
9
equivalent
With
Cpad=10pF
The natural second pole is expressed following the equation:
f
p2
+
1
2p R
comp
C
bw
(eq. 37)
The zero is expressed following the equation:
f
z
+
1
2p R
comp
C
comp
(eq. 38)
NCS29001
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15
OSCILLATOR FREQUENCY SETTING
The simplified equation to set the switching frequency using resistor R
T
:
f
sw
+
13750
R
T
) 5
(eq. 39)
Where:
R
T
is expressed in kW.
f
sw
us expressed in kHz
FBP OPTIONS
The FBP pin is used to program the feedback voltage that sets the LED current. Typically a resistor divider is used from VREF
to set the voltage between 0.5 V and 3.0 V. Additionally, to save component costs, the feedback voltage can be programmed
with internal 0.8 V (±1.5%) by tying the FBP pin to ground.
FAULT DETECTION:
• Overvoltage Protection: A resistor divider from VOUT can be used to set the overvoltage protection on the OVP pin.
When the OVP pin rises above 1.2 V the converter will shut off immediately and PWMout will be held high for 50 ms
to discharge the output capacitor. After this time the device will enter standby mode requires a high to low transition on
the STBY pin to restart.
• Short Circuit Protection: A resistor divider from VOUT can be used to set the short circuit protection on the OVP pin.
When the OVP pin drops below 75 mV the converter will shut off immediately and enter standby mode. A high to low
transition on the STBY pin is required to restart the device.
• Under Voltage Lockout (UVLO): The converter will immediately shut off and enter standby when the VIN pin voltage
drops below 7.5 V. When the UVLO condition is cleared, a high to low transition on the STBY pin is required to restart
the device.
• Temperature Shutdown: When the internal die temperature reaches 150°C, the device will behave the same as in the
overvoltage condition.
Layout Guidance
In switching converters it is important to use wide, short traces for components in the main switching path. Resistor RCS,
which is in the main switching path through transistor Q1, should be connected to power ground (PGND). Compensation
network components, resistor dividers, and bypass capacitors should be referenced to quiet ground (GND). Bypass capacitors
should be connected as close to the IC as possible.
ORDERING INFORMATION
Device Package Shipping
†
NCS29001DR2G SOIC−14
(Pb−Free)
3000 / Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

NCS29001DR2G

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Manufacturer:
ON Semiconductor
Description:
LED Lighting Drivers HV LED DRIVER
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