AN1053

Application Note 1053
Design Consideration with AP3039A
Prepared by Shanshan Yuan
System Engineering Dept.
protection to limit the output voltage. The OVP voltage can be set through external resistors. If the output
voltage is higher than the OVP high threshold point, it
will disable the driver, when the output voltage drops
to the OVP low threshold point, it will enable the
driver. It also features a soft start to reduce the inrush
current when power on, the soft start time can be set
through an external capacitor.
1. Introduction
AP3039A is a current mode high voltage low-side Nchannel MOSFET controller which is ideal for boost
regulators. It contains all the features needed to implement single ended primary topology DC/DC
converters.
The input voltage range of AP3039A is from 5V to
27V Its operation frequency is adjustable from 150kHz
to 1MHz.
2. Functional Block Description
The pin configuration and the representative block diagram of the AP3039A are respectively shown in Figure
1 and Figure 2.
The AP3039A has UVLO (Under Voltage Lock Out)
circuit. It uses two external resistors to set the UVLO
voltage. The AP3039A also has an over output voltage
SOIC-14
UVLO
1
14
SS
OV
2
13
COMP
EN
3
12
FB
VIN
4
11
SHDN
VCC
5
10
GND
OUT
6
9
CS
GND
7
8
RT
Figure 1. Pin Configuration of AP3039A (Top View)
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BCD Semiconductor Manufacturing Limited
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Application Note 1053
REFERENCE
VIN
EN
UVLO
4
3
5
1
R
22 µA
CLK
DRIVER
Q
6
7
S
2
500mV
22 µA
VCC
3V
REFERENCE
EN
1.25V
SHDN
BYPASS
SWITCH
REGULATOR
1.25V
OV
1.25V
9
LOGIC
OUT
GND
CS
+
LEB
11
SAW
+
Σ
13
COMP
OSTD
0.5V
EA
12
12 µA
14
RT
8
OSL
FB
SS
CLK
10
GND
SAW
Figure 2. Functional Block Diagram of AP3039A
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Application Note 1053
3. Operation
In Figure 3, input capacitor CIN, output capacitor
COUT, inductor L, switch Q1 and diode D1 build a
typical boost converter. The output voltage is decided
by R5, R6 and internal 0.5V reference. The output
voltage accuracy is determined by the accuracy of R5
and R6, for which the precise resistors are preferred.
(The external function will be introduced in Section 6
Application Hints)
AP3039A is a boost DC-DC controller with adjustable
operation frequency. Current mode control scheme
provides excellent line and load regulation. Operation
can be best understood by referring to the Figure 2.
At the start of each oscillator cycle, the SR latch is set
and external power switch Q1 (refer to Figure 3) turns
on. The switch current will increase linearly. The
voltage on external sense resistor RCS (refer to Figure
3), which connected from CS pin to GND, is
proportional to the switch current. This voltage is
added to a stabilizing ramp and the result is fed into
the non-inversion input of the PWM comparator.
When this non-inversion input voltage exceeds
inversion input voltage of PWM comparator, which is
the output voltage level of the error amplifier EA, the
SR latch is reset and the external power switch turns
off.
VOUT=
0.5V
* (R5 + R6 )
R6
Figure 4 is the application of driving a single 1W or
3W LED lighting. In this application, the LED current
is controlled by the feedback resistor R5. LEDs current accuracy is determined by regulator‘s feedback
threshold accuracy and is independent of the LEDs‘
forward voltage variation. So the precise resistors are
the better choices. The resistance of R5 is in inverse
proportion to the LED current since the feedback reference is fixed at 0.5V. The relation of R5 and the
LED current can be expressed as below:
It is clear that the voltage level at inversion input of
PWM comparator sets the peak current level to keep
the output in regulation. The output voltage level is the
amplified signal of the voltage difference between
feedback voltage and reference voltage of 0.5V. So, a
constant output current can be provided by this
operation mode.
R5=
0.5V
ILED
Figure 5 is the application circuit of backlight driver.
The summation of LED current is determined by R5
and internal 0.5V reference same as the illustration in
Figure 4.
4. Typical Application
V IN : 6V to 27V
L
V OUT
D1
C IN
R1
COUT
VIN
R2
UVLO
OUT
VCC
CS
CV
Q1
R5
R CS
R4
EN
OFF ON
RT
C SS
RC
R3
RT
OV
SS
FB
SHDN
COMP
OFF ON
R6
GND
CC
U1 AP3039A
Figure 3. AP3039A Application Circuit
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Application Note 1053
4. Typical Application (Continued)
L
VIN:6V to 27V
D1
CIN
R1
VIN
R3
Q1
OUT
1W or 3W LED
UVLO
CS
VCC
CV
R2
RCS
OFF ON
EN
R4
COUT
OV
RT
RT
SHDN
SS
ON OFF
CSS
FB
COMP
U1 AP3039A
GND
RC
R5
CC
Figure 4. Application Circuit 2 of AP3039A (Driving Single 1W or 3W LED Lighting)
L
VIN: 6V to 27V
D1
CIN
R1
VIN
Q1
OUT
R3
UVLO
CS
VCC
CV
R2
RCS
OFF ON
EN
R4
COUT
OV
RT
RT
SS
SHDN
ON OFF
CSS
FB
COMP
RC
GND
U1 AP3039A
R5
CC
Figure 5. Application Circuit 3 of AP3039A (Backlight Driver)
Jul. 2010 Rev. 1. 0
BCD Semiconductor Manufacturing Limited
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Application Note 1053
VIN : 6V to 27 V
CIN1
10µF
COUT
10µF
R1
VIN
UVLO
R2
OFF ON
RT
RT
10k
CS
RCS
200m Ω
A
P
3 OV
0
3
9 SHDN
A FB
EN
SS
CSS
0.1µF
R3
OUT
10* 8
R4
CH1
10* 8
CH2
SDBX
1 # AP3608E
FB
CH 1
CH8
SDB
CH 2
CH8
SDB
FBX
FB
SDBX
N # AP3608E
EN
COMP
RC
10k
GND
CC
10nF
VCC
VCC
CV
CIN2
0.1µF
EN
VCC
PWM
GND
ISET
ISET
AP3608E VCC
5.0V
External
FBX
PWM
GND
VCC
PWM
Dimming
OFF ON
Figure 6. AP3039A + AP3608E (Eight Channels Current Sink) Application Circuit
5. Components selection
Another application of AP3039A is introduced in Figure 6.
Inductor Selection
When choosing an inductor, the first step is to determine the operating mode: continuous conduction
mode (CCM) or discontinuous conduction mode
(DCM). When CCM mode is chosen, the ripple current and the peak current of the inductor can be minimized. If a small-size inductor is required, DCM
mode can be chosen. In DCM mode, the inductor ripple current and peak current are higher than those in
CCM.
The application circuit in Figure 6 is AP3039A works
with AP3608E to drive LED array. The AP3608E acts
as an eight-channel constant current sink with current
match to drive the LEDs.
The FB, FBX, SDB and SDBX pins of AP3608E are
the interface terminals to coordinate with the
AP3039A. The FB/FBX pin of AP3608E samples
voltage of each channel, and outputs the lowest
voltage of all the strings to AP3039A.
When the value of inductor is less than LCCM(MIN),
the system operates in DCM mode.
When there is a shutdown signal on EN pin of
AP3608E or all LED channels are inactive, the SDB/
SDBX pin of AP3608E outputs a low logic signal to
turn off AP3039A.
LCCM(MIN)
⎛V
= ⎜⎜ IN
⎝VOUT
⎞
⎟⎟
⎠
2
⎛VOUT −V IN
⎜⎜
⎝ I OUT * f OSC
⎞ η
⎟⎟*
⎠ 2
The expected efficiency (η) is taken from an
appropriate curve in datasheet.
If AP3608E is on PWM dimming mode, the SDB/
SDBX pin of AP3608E outputs a signal to AP3039A,
which is synchronous with PWM.
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Application Note 1053
capacitor (or two 4.7µF ceramic capacitors in parallel)
is recommended in the typical application.
Current Resistor Selection
An external resistor RCS is connected from CS pin to
GND to detect switch current signal for current-mode
boost converter. The current-limit threshold voltage
VCS of AP3039A is fixed at 500mV. The required
resistance of RCS is based on the peak inductor current
at the end of the switch on-time, and can be calculated
by the following equations:
R CS_MAX <
ΔI L =
VC S
ΔI L
+ I IN
2
(VOUT
in which,
I RMS_ON
Power MOSFET Selection
When selecting the power MOSFET Q, some
tradeoffs between cost, size, and efficiency should be
made. The losses in the MOSFET can be calculated
by:
−VIN )* VIN
L * fOSC * VOUT
PRCS = I RMS _ON 2 * RCS
2
VCC Decoupling Capacitor Selection
The VCC pin of AP3039A should be decoupled with a
ceramic capacitor placed as close to the AP3039A as
possible. This capacitor keeps VCC voltage steady
when the system operates at a high frequency. The
decoupling capacitor should adopt X5R or X7R
ceramic capacitor because of their good thermal
stability, and the capacitance of 0.47µF is
recommended.
in which,
V −VIN ⎛⎜ 2 ΔI L
= OUT
* I IN +
⎜
12
VOUT
⎝
PMOS = PCONDUCTION + PG + PSW
2
⎞
⎟
⎟
⎠
Where PCONDUCTION is conduction loss, PG is Gate
charging loss, and PSW is switching loss.
PCONDUCTION = KTH * I RMS _ ON 2 * RDSON
Output Capacitor Selection
The output capacitor of the boost converter is used for
output filtering and keeping the loop stable. The ESR
value is the most important parameter of the COUT,
because it directly affects the system stability and the
output ripple voltage.
Where KTH is the factor for the increase in on
resistance of MOSFET due to heating. For an
approximate analysis, the factor can be ignored and
the maximum on resistance of the MOSFET can be
used.
The total output ripple can be calculated by the
following the equations:
Gate charging loss, PG, results from the current
required to charge and discharge the Gate capacitance
of the power MOSFET and is approximated as:
ΔVo = ΔVO(CO) + ΔVO(ESR)
ΔVO(CO) =
I OUT
*
CO
⎛ VOUT - V IN
⎜⎜
⎝VOUT * f OSC
PG = Qg *VCC * f OSC
⎞
⎟⎟
⎠
Where Qg is the total Gate charge of the MOSFET.
Power of VCC is applied by VIN and the MOSFET
driving current flows through VCC regulator. The loss
PVCC is estimated as:
ΔVO(ESR) = I L _ PEAK * R ESR(CO)
The small size and high temperature rating of ceramic
capacitors is a good choice.
PVCC = (VIN − VCC ) ∗ Qg ∗ f OSC
Input Capacitor Selection
The input capacitor (CIN) of AP3039A filters the
current peaks drawn from the input supply and
reduces noise injection into the IC. A 10µF ceramic
So the total Gate charging loss is
PG_TOTAL = PG + PVCC
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Application Note 1053
ters RCOMP and CCOMP in different operating frequency (as shown in Figure 4) are shown in table 1.
The total Gate charging loss occurs in IC but not in the
MOSFET itself only actually.
Switching loss, PSW, occurs in transition period as the
MOSFET turns on and off. This loss is consisted of
turn on loss and turn off loss.
Operating Frequency (kHz)
ΔI L
1
PTURN_ON = (I IN ) * VOUT * t r * fOSC
6
2
1
ΔI L
PTURN_OFF = (I IN +
) * VOUT * t F * fOSC
6
2
ΔI L =
(VOUT −VIN )* VIN
CCOMP (nF)
200
15
3.3
400
15
3.3
600
22
3.3
800
36
3.3
1000
51
2.2
6. Application Hints
Input Under-Voltage Detector
AP3039A contain an Under Voltage Lock Out
(UVLO) circuit. Two resistors R1, R2 are connected
from UVLO pin to ground and the VIN pin (refer to
Figure 3.). The resistor divider must be designed such
that the voltage on the UVLO pin is higher than 1.25V
when VIN is in the desired operating range. If this
under voltage threshold is not met., all functions of
AP3039A are disabled and system remains in a low
power standby state. UVLO hysteresis is
accomplished through an internal 22µA current
Source that is switched on or off into the impedance of
the set-point divider. When the UVLO threshold is
exceeded, the current Source is activated to instantly
raise the voltage on the UVLO pin. When the UVLO
pin voltage falls below the threshold the current
Source is turned off, causing the voltage on the UVLO
pin to fall. The formula for UVLO can be expresses as
blow:
For Input Threshold Voltage
PSW = PTURN _ ON + PTURN _ OFF
Where tR and tF are the rise and fall times of the MOSFET.
When MOSFET turns off, the VDS (the stress voltage
on Drain to Source ) of MOSFET is VOUT plus the
ringing. The MOSFET selected must be able to withstand VOUT plus any ringing from drain to Source, and
VCC plus ringing from Gate to Source. The MOSFET
with VDS =60V and VGS> 10V is recommended.
Diode Selection
The boost converter requires a diode D to carry the
inductor current during the MOSFET off time.
Schottky diodes are recommended due to their fast
recovery time and low forward. D should be rated to
handle the maximum output voltage (plus switching
node ringing) and the peak switch current. The conduction loss of diode is calculated by:
VIN_THRESHOLD = 1.25V * ((R1 + R2))
R2
For Input Hysteresis Voltage
in which,
VIN_HYSTERESIS = 22µA*R1
1
I RMS_OFF
RCOMP (kΩ)
Table 1. Compensation Selection
L * fOSC * V OUT
PDIODE = I RMS _ OFF *VF
Compensation Parameter
⎡V
⎛
ΔI L 2 ⎞⎟ ⎤ 2
2
= ⎢ IN * ⎜⎜ I I N +
⎥
12 ⎟⎠ ⎥⎦
⎢⎣V OUT ⎝
Over-Voltage Protection
AP3039A has an over voltage protection (OVP)
circuit. The OV Pin is connected to the center tap of a
resistive voltage-divider from the high voltage output
to GND (refer to Figure 3.). When the loop is open or
the output voltage becomes excessive in any case,
result the voltage on OV pin exceeds 1.25V, all
functions of AP3039A are disabled, and the output
voltage will fall. OVP hysteresis is accomplished with
the VF is the forward voltage of Schottky diode.
RCOMP and CCOMP Selection
AP3039A adopts current mode PWM control to
improve transient response and achieve simple loop
compensation circuit. The loop compensation parame-
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Application Note 1053
MOSFET driver. On the condition that VIN≥13.5V, the
regulator generates a 10V supply. If 6V≤VIN≤12.5V,
the VCC is equal to VIN minus drop voltage across
bypass switch. When VIN is less than 6V, connect
VCC to VIN.
an internal 22µA current Source and the operation
mode is the same as UVLO. The formula for OVP can
be expresses as blow:
For OVP Voltage
VOVP =1.25V ∗(
(R3 + R4)
)
R4
7. PCB Layout Guideline
Boost converter performance can be seriously affected
by poor layout. To produce an optimal solution for
system, good layout and design of the PCB are as
important as the component selection. The following
PCB layout guideline should be considered:
For OVP Hysteresis Voltage:
VOVP_HYSTERESIS = 22µA*R3
Frequency Selection
An external resistor RT connected from RT pin to
GND to set the operating frequency (refer to Figure 3).
Operation frequency range is from 150kHz to 1MHz
(as shown in Table 2). High frequency operation optimizes the regulator for the smallest component size,
while low frequency operation can reduce the switch
losses.
RT (kΩ)
Operating Frequency (kHz)
470
150
390
200
147
400
95
600
68
800
51
1000
1. There are two high-current loops in the solution.
One is the high-current input loop, and the other is the
high-current output loop. The high-current input loop
goes from the positive terminal of the CIN to the
inductor, to the MOSFET, then to the current-sense
resistor, and to the CIN’s negative terminal. The highcurrent output loop goes from the positive terminal of
the CIN1 to the inductor, to the diode, to the positive
terminal of the COUT, reconnecting between the COUT
and the CIN ground terminals. Minimize the area of
the two high-current loops to avoid excessive switching noise. The trace connected these two high-current
loops must be short and thick.
2. Create two ground islands. One is called Power
Ground Island (P Island), the other is called Analog
Ground Island (A Island). The P Island consists of
CIN and COUT ground connections and negative terminal of the current-sense resistor RCS. Maximizing the
width of the P Island traces will improve efficiency
and reduces output voltage ripple and noise spike. The
A Island is the connection of the OV and UVLO
detection-divider ground, RT resistor ground, CV, CSS,
Table 2. Frequency Selection
Soft Start
The AP3039A has a soft start circuit to limit the inrush
current during startup. The soft start feature allows the
boost converter output to gradually reach the initial
steady state output voltage, thereby reducing start-up
stresses and current surges. The time of startup time is
controlled by an internal 12µA current Source and an
external soft start capacitor CSS which connected from
SS pin to GND (refer to Figure 4). At power on, after
the VIN UVLO threshold is reached, the internal 12µA
current Source charges the external capacitor CSS. The
capacitor voltage will ramp up slowly and will limit
COMP pin voltage and the switch current.
and CCOMP ground and the device’ s exposed backside pad. Connect the P Island and A Island directly to
the exposed backside pad. Make no other connections
between these separate ground planes.
3. Place the bypass capacitor CV as close to the device
as possible. The ground connection of these capacitors
should be connected directly to GND pins with a thick
trace.
VCC Pin Application Description
The AP3039A includes an internal low dropout linear
regulator with the output pin VCC. This pin is used to
power internal PWM controller, control logic and
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