AN8014 [PANASONIC]
Step-down, step-up, or inverting DC-DC converter control IC; 降压，升压或反相DC -DC转换器控制IC
| 型号： | AN8014 |
| 厂家： | 
PANASONIC |
| 描述： | Step-down, step-up, or inverting DC-DC converter control IC |
| 文件： | 总18页 (文件大小：152K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Voltage regulators
AN8014S
Step-down, step-up, or inverting DC-DC converter control IC
■ Overview
Unit: mm
The AN8014S is a single-channel PWM DC-DC
converter control IC.
10.1±0.3
16
9
This IC can provide any one output type from
among step-down, step-up and inverting output.
Allowing n-channel power MOSFET direct driv-
ing, the AN8014S is ideal for high-efficiency power
supplies.
(0° to 10°)
0.3
1
8
■ Features
• Wide operating supply voltage range (3.6 V to 34 V)
(The voltage is limited within a range between 3.6
V and 17 V if it is connected to a step-down volt-
age circuit.)
1.27
(0.605)
0.40±0.25
Seating plane
Seating plane
•
Totem pole output circuit: output peak current (±1 A)
SOP016-P-0225A
• On-chip pulse-by-pulse overcurrent detection and
protection circuit
Threshold voltage VCC − 0.095 V typical
• On-chip bootstrap circuit (allowing n-channel MOSFET direct driving.)
• On-chip under-voltage lock-out circuit (U.V.L.O.)
• On-chip on/off function (active-high control input, standby current of maximum 5 µA)
• On-chip timer latch short-circuit protection circuit
• Maximum oscillator frequency (500 kHz)
■ Applications
• DC-DC switching power supply
■ Block Diagram
Triangular
wave OSC
VREF
2.5V
10
Constant
current
source
CLM
Latch
Q
R
S
On/off
16
OFF
1 µA
10 µA
active-high
15
14
Boot
strap
VCC
CB
R
S
Q
U.V.L.O.
Q
PWM
comp.
13
R
S
Out
Q
Latch
5
S.C.P.
6
7
IN+
IN−
Error amp.
S.C.P.
comp.
1
AN8014S
Voltage regulators
■ Pin Descriptions
Pin No.
Description
Pin No.
9
Description
1
2
3
4
5
Internal reference output
Not connected
Oscillator timing resistor connection
Oscillator timing capacitor connection
Dead-time control
10
Overcurrent protection input
Signal ground
11
12
Output stage ground
Totem pole type output
Bootstrap output
13
Capacitance connection for short-circuit
protection delay
14
6
7
8
Error amplifier noninverting input
Error amplifier inverting input
Error amplifier output
15
Supply voltage
16
On/off control
■ Absolute Maximum Ratings
Parameter
Symbol
VCC
ICC
Rating
Unit
V
Supply voltage
35
Supply current
mA
mW
°C
°C
V
2
Power dissipation *
PD
143
−30 to +85
−40 to +125
VCC
1
Operating ambient temperature *
Topr
1
Storage temperature *
Tstg
On/off pin allowable application voltage VON/OFF
Error amplifier allowable input voltage
DTC pin allowable application voltage
Out pin allowable application voltage
Out pin constant output current
Out pin peak output current
VI
VDTC
VOUT
IO
− 0.3 to VREF
− 0.3 to VREF
35
V
V
V
±100
mA
mA
V
IO(Peak)
VCB
±1 000
CB pin allowable application voltage
CB pin constant output current
35
ICB
−100, 150
−500, 1 000
VCC
mA
mA
V
CB pin peak output current
ICBP
CLM pin allowable application voltage
VCLM
Note) 1. 1: Except for the operating ambient temperature and storage temperature, all ratings are for T = 25°C.
*
a
2: At T = 85°C
*
a
2. Do not apply external currents or voltages to any pins not specifically mentioned.
For circuit currents, '+' denotes current flowing into the IC, and '−' denotes current flowing out of the IC.
■ Recommended Operating Range
Parameter
Supply voltage
Symbol
Range
Step-up circuit system
Step-down circuit system
Unit
VCC
3.6 to 34
3.6 to 17
V
2
Voltage regulators
AN8014S
■ Electrical Characteristics at VCC = 12 V, Ta = 25°C
Parameter
Reference voltage block
Output voltage
Symbol
Conditions
Min
Typ Max Unit
VREF
Line
Load
IREF = −1 mA
2.522 2.6 2.678
V
Line regulation with input fluctuation
Load regulation
VCC = 3.6 V to 34 V
16
1
25
10
mV
mV
IREF = − 0.1 mA to −1 mA
U.V.L.O. block
Circuit operation start voltage
Hysteresis width
VUON
VHYS
2.8
60
3.1
3.4
V
140
180
mV
Error amplifier block
Input offset voltage
VIO
IB
−6
6
mV
nA
V
Input bias current
−500 −25
− 0.1
Common-mode input voltage range VICR
0.8
High-level output voltage
VEH
VREF VREF
V
− 0.3 − 0.1
Low-level output voltage
Dead-time control circuit block
Input current
VEL
0.1
0.3
V
IDTC
−15.8 −13.2 −10.6
µA
V
Low-level input threshold voltage
High-level input threshold voltage
Output block
VDT-L
Duty 0%
0.45 0.65
VDT-H Duty 100%
1.2
1.4
V
Oscillator frequency
fOUT
Du
CT = 120 pF, RT = 15 kΩ
196
47
218
52
240
57
kHz
%
Output duty
RDTC = 75 kΩ
IO = 70 mA
Low-level output voltage
High-level output voltage
VOL
VOH
1.0
1.3
V
IO = −70 mA
VCB VCB
V
−2.0 −1.0
Bootstrap circuit block
Input standby voltage
VINCB ICB = −70 mA
VCC VCC VCC
V
−1.2 −1.0 − 0.8
Short-circuit protection circuit block
Input threshold voltage
Input standby voltage
Input latch voltage
VTHPC
VSTBY
VIN
0.70 0.75 0.80
V
30
30
120
120
mV
mV
µA
Charge current
ICHG
−2.76 −2.30 −1.84
On/off control block
Threshold voltage
VTH
0.8
2.0
V
V
Overcurrent protection block
Threshold voltage
VCLM
VCC VCC VCC
− 0.115 − 0.095 − 0.075
3
AN8014S
Voltage regulators
■ Electrical Characteristics at VCC = 12 V, Ta = 25°C (continued)
Parameter
Whole device
Symbol
Conditions
Min
Typ Max Unit
Total consumption current
Standby current
ICC
5.0
7.0
5
mA
ICC(SB)
µA
• Design reference data
Note) The characteristics listed below are theoretical values based on the IC design and are not guaranteed.
Parameter
Symbol
Conditions
Limit
Unit
Reference voltage block
Output voltage temperature
characteristics 1
VTC1
VTC2
IOS
Ta = −30°C to +25°C
Ta = 25°C to 85°C
±1
±1
%
%
Output voltage temperature
characteristics 2
Output short-circuit current
Error amplifier block
Output sink current
Output source current
Open-loop gain
−40
mA
ISINK VFB = 0.9 V
ISOURCE VFB = 0.9 V
AG
8
mA
µA
dB
−110
70
Output block
Frequency supply voltage
characteristics
fdV
fdT1
fdT2
fOUT = 200 kHz,
VCC = 3.6 V to 34 V
±3
±9
±9
%
%
%
Frequency temperature
characteristics 1
fOUT = 200 kHz,
Ta = −30°C to +25°C
Frequency temperature
characteristics 2
fOUT = 200 kHz,
Ta = 25°C to 85°C
Oscillator block
RT pin voltage
VRT
0.4
1.87
200
V
V
Short-circuit protection circuit block
Comparator threshold voltage
Overcurrent protection circuit block
Delay time
VTHL
tDLY
ns
4
Voltage regulators
AN8014S
■ Terminal Equivalent Circuits
Pin No. I / O
Equivalent circuit
Description
1
O
VREF:
VCC
Outputs the reference voltage
2.6 V (allowance: 3%)
Incorporating short-circuit protection
against ground.
VREF
1
2
RT:
VREF
Connection for the timing resistor which
decides the oscillator frequency. Use a re-
sistor in the range 5.1 kΩ to 30 kΩ. The
pin voltage is approx. 0.4 V.
DTC
S.C.P.
100 Ω
RT(≈ 0.4 V)
2
3
CT:
VREF
Connection for the timing capacitor which
decides the oscillator frequency. Use a ca-
pacitor in the range 100 pF to 10 000 pF.
For the oscillator frequency setting, refer
to the "Application Notes, [1] Function
descriptions" section. Use an oscillator fre-
quency in the range 5 kHz to 500 kHz.
To PWM input
IO
CT
3
OSC
comp.
2IO
4
DTC:
VREF
Connection for a resistor and a capacitor
that set the dead-time and soft start period
of PWM output.
PWM comparator
input
Input current IDTC is decided by the timing
resistor RT which controls sample to sample
variations and temperature variations.
It is approx. −13.2 µA when RT = 15 kΩ.
IDTC
4
DTC
CDTC
RDTC
VRT
RT
1
2
IDTC
=
×
[A]
2
RT
5
AN8014S
Voltage regulators
■ Terminal Equivalent Circuits (continued)
Pin No. I / O
Equivalent circuit
Description
5
S.C.P.:
Connection for the capacitor that sets the
soft start period and the timer latch short-
circuit protection circuit time constant.
Use a capacitor with a value of 1 000 pF
or higher.
VREF
ICHG
Latch
S
Q
R
U.V.L.O.
output
The charge current ICHG is decided by the
timing resistor RT which controls sample
to sample variations and temperature varia-
tions.
0.75 V
It is approx. −2.3 µA when RT = 15 kΩ.
5
S.C.P.
VRT
1
ICHG
=
×
[A]
RT 11
6
7
I
I
IN+:
VREF
Noninverting input to the error amplifier.
Use the common-mode input in the range
− 0.1 V to +0.8 V.
IN−:
Inverting input to the error amplifier.
Use the common-mode input in the range
− 0.1 V to +0.8 V.
7
6
IN−
IN+
8
O
FB:
VREF
Output from the error amplifier.
The source current is approx. −110 µA and
sink current is approx. 8 mA.
Correct the frequency characteristics of
the gain and the phase by connecting a re-
sistor and a capacitor between this pin
and IN− pin.
Source current
8 FB
Sink current
9
N.C.: Not connected.
10
I
CLM:
VCC
0.1 V
10
CLM
Detects the overcurrent state in switching
transistor.
Insert a resistor with a low resistance between
this pin and VCC to detect overcurrent states.
When this pin falls to a level 95 mV or
more lower than VCC , the PWM output is
turned off for that period thus narrowing
the width of the on-period.
CLM
comp.
50 µA
50 µA
(This implements a pulse-by-pulse
overcurrent protection technique.)
6
Voltage regulators
AN8014S
■ Terminal Equivalent Circuits (continued)
Pin No. I / O
Equivalent circuit
Description
SGND: Signal ground.
11
SGND
11
12
12
GND: Output stage ground.
GND
13
14
O
O
Out:
Totem pole output.
VCC
A constant output current of ±100 mA or a
peak output current of ±1 A can be ob-
tained.
14
CB
CB:
Bootstrap output.
13 Out
Connect a bootstrap capacitor between
this pin and the n-channel MOSFET source-
side pin of the switching element when
using a step-down voltage circuit.
Short-circuit this pin and the VCC pin when
using a step-up voltage circuit.
15
16
I
I
V
CC: Power supply.
15
VCC
:
OFF
Controls the on/off state.
OFF
16
When the input is high: normal operation
(VOFF > 2.0 V)
17 kΩ
When the input is low: standby mode
(VOFF < 0.8 V)
13 kΩ
In standby mode, the total current consu-
mption is held to under 10 µA.
■ Application Notes
[1] Function descriptions
1. Reference voltage block
This block is composed of the band gap circuit and outputs the temperature compensated reference voltage (2.6
V) to the VREF pin (pin 1). The reference voltage is stabilized when the supply voltage is 3.6 V or more and used
as the operating power supply in IC. It is possible to take out a load current of up to −1 mA.
7
AN8014S
Voltage regulators
■ Application Notes (continued)
[1] Function descriptions (continued)
2. The triangular wave generator block (OSC)
The triangular wave which swings from approximately 1.32 V (upper limit value, VOSCH) to approximately 0.44
V (lower limit value, VOSCL) will be generated by connecting a timing capacitor CT and a resistor RT to the CT pin
(pin 3) and RT pin (pin 2) respectively. Oscillator frequency can be freely decided by the value of CT and RT
connected externally. The oscillator frequency fOSC is obtained by the following formula;
VCTH = 1.32 V (typ.)
1
IO
2 × CT × (VCTH − VCHL
0.4
fOSC
=
=
t1 + t2
VRT
)
IO = 1.7 ×
= 1.7 ×
RT
RT
Because VCTH − VCTL = 0.88 V
VCTL = 0.44 V (typ.)
1
t1
t2
fOSC
≈
[Hz]
2.59 × CT × RT
Charging Discharging
T
Example) An fOSC of approximately 215 kHz will be
obtained if CT is 120 pF and RT is 15 kΩ.
Figure 1. Triangular oscillation waveform
It is possible to use the circuit in the recommended operating range of 5 kHz to 500 kHz of the oscillator
frequency. As the AN8014S is used at increasingly higher frequencies, the amount of overshoot and undershoot
due to the operation delay in the triangular wave oscillator comparator increases, and discrepancies between the
values calculated as described previously and the actual values may occur.
The output source currents of the AN8014S's S.C.P. and DTC pins are determined by the timing resistor RT
which is externally connected to the RT pin. Therefore, note that this IC can not be used as an IC for slave when
the several ICs are operated in parallel synchronous mode.
3. Error amplifier block
Detecting and amplifying DC-DC converter output voltage, the error amplifier with PNP transistor input inputs
the signal to the PWM comparator.
Figure 2 shows the way to connect the error amplifier.
The common-mode input voltage range is − 0.1 V to + 0.8 V, and a voltage obtained by dividing the reference
voltage with built-in resistors is applied to the non-inverting input. Connecting the feedback resistor and the
capacitor between the error amplifier output pin (pin 8) and the inverting input pin (pin 7) allows the arbitrary gain
setting and the phase compensation.
Startup overshooting caused by feedback delays will be suppressed by setting the output source current and
output sink current to as high as 110 µA and 8 mA respectively.
The input voltage VIN+ and VIN− to the error amplifier are obtained from the following formulas.
R4
R3 + R4
R2
R1 + R2
VIN+ = VREF
×
VIN− = VOUT ×
1
VREF
IN+
IN−
R3
PWM comparator
CT
DTC
Error
amp.
6
13
VOUT
R1
7
R4
8
RNF
FB
R2
CNF
Figure 2. Connection method of error amplifier
8
Voltage regulators
AN8014S
■ Application Notes (continued)
[1] Function descriptions (continued)
4. Timer latch short-circuit protection circuit
This circuit protects external main switching devices, flywheel diodes, choke coils and so forth from breakdown
or deterioration when overload or short-circuit of power supply lasts a certain time.
Figure 3 shows the short-circuit protection circuit. The timer latch short-circuit protection circuit detects the
output level of the error amplifier.
If the output voltage of the DC-DC converter is stable, the output of the error amplifier from the FB pin is stable
and the short-circuit protection comparator is well balanced.
In that case, the transistor Q1 is conductive and the S.C.P. pin voltage is approximately 30 mV constantly.
If the load condition changes radically and output signal voltage of the error amplifier (FB) is 1.87 V or
higher, the short-circuit protection comparator outputs low-level voltage. Then, by cutting off the transistor Q1,
the external capacitor CS of S.C.P. pin (pin 5) starts charging with the current ICHG which is obtained from the
following formulas.
tPE
CS
V
PE = VSTBY + ICHG
×
[V]
tPE
0.75 V = 0.03 V + ICHG
×
CS
tPE
CS = ICHG
×
[F]
0.72
CHG is constant current which is determined by the timing resistor RT .
If RT is 15 kΩ, ICHG will be approximately 2.3 µA.
I
VRT
RT
1
11
ICHG
=
×
[A]
When the external capacitor CS is charged up to approximately 0.75 V, the latch circuit will be turned on. Then
the totem-pole output pin will be set to low level and the dead-time will be set to 100%.
When the latch circuit is turned on, the S.C.P. pin will discharge electricity till the voltage on the S.C.P. pin
reduces to approximately 30 mV. The latch circuit cannot be, however, reset until power supply to the AN8014S
is turned off.
VREF
ICHG
S.C.P.
comp.
S
Q
Q
Error amp.
Cut output off
6
7
IN+
IN−
R
Latch
Q1
8
FB
Q2
1.82 V
5
S.C.P.
CS
Figure 3. Short-circuit protection circuit
5. Low input voltage malfunction prevention circuit (U.V.L.O.)
This circuit protects system from breakdown or deterioration caused by malfunction in control circuit when
supply voltage is dropped during transient time at power on or off.
The low input voltage malfunction prevention circuit detects internal reference voltage which changes in
accordance with the supply voltage level. When the supply voltage is turned on, it sets the dead-time of Out pin
(pin 13) to 100% and keeps the DTC pin (pin 4) and S.C.P. pin (pin 5) low level until the supply voltage reaches
3.1 V. When the supply voltage falls, it will operate even below 2.96 V because of its hysteresis width of 140 mV.
9
AN8014S
Voltage regulators
■ Application Notes (continued)
[1] Function descriptions (continued)
6. Remote circuit
It is possible to switch on or off the IC control by using an external control signal. When the OFF pin (pin 16)
voltage is lowered to below approximately 0.8 V, the internal reference voltage goes down thereby stopping the
IC control and reducing the circuit current to 5 µA or less. When the OFF pin voltage is increased to approximately
2.0 V or more, the internal reference voltage rises thereby starting the control operation.
7. PWM comparator block
The PWM comparator controls the on-period of output pulse in accordance with the input voltage. While the
triangular wave voltage on the CT pin (pin 3) is lower than both the error amplifier's output voltage on pin 8 and
the voltage on the DTC pin (pin 4), the output on the Out pin (pin 13) will be set to high level. Then the switching
element (n-channel MOSFET) will be turned on.
The dead-time is set by adjusting the voltage VDTC on the DTC pin (pin 5) as shown in figure 4.
The DTC pin has constant current output determined by the resistor RT . Therefore VDTC is adjusted by
connecting the DTC and GND pins through the external resistor RDTC
.
When the oscillator frequency fOSC is 200 kHz, the output duty cycle will be 0% at VDTC of 0.44 V typical and
100% at VDTC of 1.32 V typical.
The levels of overshooting and undershooting of the peak value VCTH and the trough value VCTL of the
triangular wave vary with the oscillator frequency.
VREF
IDTC
VCTH
VDTC
VCTL
CT waveform
DTC
waveform
PWM
CT
FB
tOFF
Off
tON
On
DTC
RDTC
Out waveform
Off
CDTC
Figure 4. Setting the dead-time
Output duty ratio Du and DTC pin voltage VDTC are expressed by the following formulas;
tON
ON − tOFF
VDTC − VCTL × 1.1
(VCTH − VCTL) × 1.1
Du =
× 100 [%] =
× 100 [%]
t
VRT
RT
1
2
IDTC
=
×
[A]
RDTC
RT
1
2
VDTC = IDTC × RDTC = VRT
×
×
[V]
Example) When fOSC = 215 [kHz] (RT = 15 kΩ, CT = 120 pF) and RDTC = 75 [kΩ]
CTH is approximately 1.32 V, VCTH is approximately 0.44 V, and VRT is approximately 0.4 V.
Therefore, the following are obtained.
DTC ≈ 13.3 [µA]
DTC ≈ 0.99 [V]
V
I
V
Du ≈ 52.3 [%]
There may be an operational delay of the PWM comparator and a difference in peak and trough values of the
triangular wave oscillation. Discrepancies between the values obtained from the above formulas and the actual
values may occur, in which case adjust the values on the mounting substrate.
In starting, if the capacitor CDTC is added in parallel to the external resistor RDTC , and the output pulse width
are gradually widened, the AN8014S will be in soft-start operation. Thus the overshoot at the output of DC-DC
converters can be prevented.
10
Voltage regulators
AN8014S
■ Application Notes (continued)
[1] Function descriptions (continued)
8. Overcurrent protection block
Utilizing that the overcurrent of power output is proportional to the current value which flows in the main switch
(power MOSFET), the block regulates the upper limit of the current flowing in the main switch, thus protects the
parts such as main switch device, a flywheel diode and a choke coil from the damage caused by the overcurrent.
The current detection are done by monitoring, at CLM pin (pin 10), the voltage drop in resistor which is placed
between the main switch device and VCC pin.
When the main switch device (power MOSFET) is switched on and the voltage of CLM pin reaches "VCC
−
95 mV", threshold level for overcurrent detection, the output drive transistor is cut off so that no more current
flows in the main switch device. This control is repeated at each cycle. When overcurrent is detected once, the
transistor remains off during the same cycle, and is switched on in the next cycle.
Such an overcurrent detection method is called "Pulse-by-pulse overcurrent detection."
(3) Output Off
(5) Turned on in the next cycle
1.32 V
0.44 V
Triangular wave (CT)
Error amplifier output (FB)
High
Low
Output waveform (Out)
VCC
Overcurrent protection input (CLM)
VCC − 95 mV
(1) Overcurrent detection
(2) Latch set
Latch circuit set signal
tDLY : Delay time
High
Low
High
Low
Latch circuit reset signal
(4) Latch reset
Figure 5. Waveforms of the pulse-by-pulse overcurrent protection operation
R2 and C1 shown in figure 6 constitute a low-pass
filter to eliminate noise due to parasitic capacitance when
the power MOSFET is turned on.
The cut-off frequency of the filter is obtained from
the following.
R2
C1
R1
Out
In
1
fC =
[Hz]
2πC1R2
V-Out CLM
Figure 6. CLM noise filter circuit
11
AN8014S
Voltage regulators
■ Application Notes (continued)
[1] Function descriptions (continued)
9. Bootstrap circuit of output block
If the n-channel MOSFET is used as a switching device for DC-DC converter control of step down method,
a bootstrap circuit is required.
Bootstrap circuit ensures that the gate-source voltage is gate threshold voltage or higher by going up the high
level of the Out pin (pin 13) than VCC voltage when n-channel MOSFET turns on. Figure 7 shows the output of
bootstrap circuit including the external circuit. Figure 8 shows the operating waveform of the bootstrap circuit.
VS
M1
V-Out
VCC
15
VGS
CB
SBD
VD1
I1
D1
14 CB
I2
PWM comparator
CT
DTC
FB
Q1
VCB
Out
13
Q2
Figure 7. Bootstrap circuit of output block
VCBH
VOH
Turns off
VCC
VCC −VDS(ON) [V]
VCC − 0.7 [V]
CB pin waveform
Turns off
Out pin waveform
VOL
−VF
0 V
M1 source side waveform
t1
t2
t3
M1 Off
M1 Off
M1 On
Figure 8. Bootstrap circuit operating waveform
The following describes the operation of the bootstrap circuit.
1) N-channel MOSFET (M1) off time: t1
While the M1 is turned off, the choke coil is provided with energy from the schottky barrier diode (SBD)
and the source-side voltage VS of the M1 is fixed to −VF. The bootstrap capacitor CB is charged from the VCC
pin (pin 15) through the AN8014S's internal diode D1.
The voltage VCB on the CB pin (pin 14) is expressed by the following.
VS = −VF
VCB = VCC − VD1
VF : Forward voltage of SBD
V
D1: Forward voltage of D1
Therefore, the charged voltage of bootstrap capacitor CB is expressed by the following.
CB − VS = VCC − VD1 + VF
V
12
Voltage regulators
AN8014S
■ Application Notes (continued)
[1] Function descriptions (continued)
9. Bootstrap circuit of output block (continued)
2) N-channel MOSFET (M1) turn-on time: t2
When the PWM comparator output is inverted, the Out pin (pin 13) output changes into a high level. The
Out pin voltage VO rises toward the CB pin voltage.
VO = VCB − VCE(sat)
Then the voltage between the gate and source of the M1 is obtained from the following.
VGS = VO+VF
When the Out pin voltage VO is the same as or higher than the gate threshold voltage VTH , the M1 turns
on. Then the M1 source-side voltage rises up to the voltage expressed by the following.
VS = VCC − VDS(ON)
The bootstrap capacitor CB is connected to the source side and CB pin of the M1. Therefore, the CB pin
voltage rises according to the M1 source-side voltage due to capacitor coupling. VCB is expressed by the
following formula.
VCB = VS + VCC − VD1 + VF
= 2 × VCC − VD1 + VDS(ON) + VF
3) N-channel MOSFET (M1) turn-off time: t3
The Out pin voltage turns off after rising to the saturation voltage of the AN8014S's internal transistor Q1.
The M1 source-side voltage drops to −VF . The CB pin voltage drops to VCC − VD1 or below due to capacitive
coupling. Then the M1 will be in the state described in the above 1).
[2] Bootstrap circuit usage notes
1. Operating voltage range for step-down circuit
Just like what described previously, if a step-down circuit is in DC-DC converter control, the CB pin (pin 14)
voltage will be approximately twice as high as VCC when the n-channel MOSFET as a switching element is turned
on. The allowable voltage applied to the CB pin is 35 V. Therefore the operating supply voltage must be within a
range between 3.6 V and 17 V.
V
CB = 2 × VCC − VD1 − VDS (ON) + VF < 35 [V]
35 + VD1 + VDS (ON) − VF
VCC
<
[V] < 17 [V]
2
2. Value setting of bootstrap capacitor
The bootstrap capacitor raises the CB pin voltage to VCC or higher due to capacitor coupling to the source side
of the n-channel MOSFET when the n-channel MOSFET is turned on. At that time bootstrap capacitor is dis-
charged by n-channel MOSFET gate-drive-current. If the capacitance of the bootstrap capacitor is too low, an
increase in switching loss will result, which will reduce the efficiency.
Therefore, the capacitance must be large enough in comparison with the gate input capacitance of the n-
channel MOSFET. Refer to the following.
CB > Ciss
Determine the best value by testing on the printed circuit board for mounting.
3. CB pin connection for step-up circuit
If a step-up circuit is in DC-DC converter control, no bootstrap circuit is required because the source side of
the n-channel MOSFET is grounded. Therefore, short-circuit the CB pin (pin 14) and the VCC pin (pin15).
Thus, the operating supply voltage range in the step-up circuit method is between 3.6 V and 34 V.
13
AN8014S
Voltage regulators
■ Application Notes (continued)
[3] Timing chart
High
OFF pin voltage
Low
3.6 V
Supply voltage (VCC
)
Error amplifier output (FB)
Internal reference voltage
2.6 V
Power supply
turning on
1.87 V
1.32 V
DTC pin voltage
Triangular wave (CT)
0.44 V
0.03 V
High
S.C.P. pin voltage
Out pin waveform
Low
Software start operation
The maximum duty
Figure 1. PWM comparator operation waveform
Internal reference voltage
2.6 V
Short-circuit protection comparator
(threshold level)
1.87 V
1.32 V
0.44 V
DTC pin voltage
Error amplifier output (FB)
Triangular wave (CT)
High
Out pin waveform
S.C.P. pin voltage
Low
0.75 V
0.03 V
High
Short-circuit protection
comparator output
tPE
Low
Figure 2. Short-circuit protection operation waveform
14
Voltage regulators
AN8014S
■ Application Notes (continued)
[3] Timing chart (continued)
Output off
Turned on in the next cycle.
1.32 V
0.44 V
Triangular wave (CT)
Error amplifier output (FB)
High
Out pin waveform
Low
VCC
Overcurrent protection input (CLM)
VCC − 95 mV
Overcurrent
tDLY: Delay time
detection
Latch set
High
Low
High
Low
Latch circuit set signal
Latch circuit reset signal
Latch reset
Figure 3. Waveforms of the pulse-by-pulse overcurrent protection operation
[4] PD
Ta curves of SOP016-P-0225A
PD
Ta
600
Glass epoxy printed
circuit board
518
500
(50 mm × 50 mm × t0.8 mm)
Rthj−a = 263°C/W
PD = 380 mW (25°C)
400
360
Independent IC
without a heat sink
Rthj−a = 278°C/W
PD = 360 mW (25°C)
300
207
200
143
100
0
0
25
50
75 85 100
125
150
Ambient temperature Ta (°C)
15
AN8014S
Voltage regulators
■ Application Notes (continued)
[5] Main characteristics
Internal reference voltage temperature characteristics
Oscillator frequency temperature characteristics
2.63
225
220
215
210
2.62
205
200
195
2.61
2.60
−50 −25
0
25
50
75
100
125
−50 −25
0
25
50
75
100
125
Ambient temperature Ta (°C)
Ambient temperature Ta (°C)
Output duty ratio
DTC pin voltage
Output duty ratio temperature characteristics
100
80
60
40
20
0
56
55
54
53
52
51
50
0.4
0.6
0.8
1.0
1.2
1.4
−50 −25
0
25
50
75
100
125
DTC pin voltage VDTC (V)
Ambient temperature Ta (°C)
Oscillator frequency Timing capacitance
Output peak current COut
10 000
0.6
0.5
0.4
0.3
VCC = 12 V
OUT = 10 Ω
R
1 000
100
10
RT = 5.1 kΩ
RT = 15 kΩ
0.2
0.1
0
1
10
100
1 000
10 000
1 000
5 000
10 000
Timing capacitance CT (pF)
Value of output connection capacitor COUT (pF)
16
Voltage regulators
AN8014S
■ Application Circuit Examples
1. DC-DC converter control (Example of step-down circuit)
0.1 Ω
Out
5 V
In
12 V
3.9 kΩ
100 µF
33 Ω
V1
0.1 µF
75 kΩ
0.039 µF
1 000 pF
120 pF
9.1 kΩ
47 µF
15 kΩ
10 Ω
f = 200 kHz
Triangular
wave OSC
10
VREF
2.5V
Constant
CLM
VCC
Latch
current source
R
Q
S
16
On/off
active-high
15
14
OFF
1 µA
10 µA
Boot
strap
In
CB
R
Q
U.V.L.O.
Q
S
PWM
comp.
Out
13
R
S
Q
Latch
S.C.P.
5
IN+
IN−
6
7
62 kΩ
11 kΩ
0.12 µF
Error amp.
S.C.P.
comp.
100 kΩ
2. DC-DC converter control (Example of step-up circuit)
In
Out
V1
Triangular
wave OSC
10
VREF
2.5V
Constant
CLM
Latch
Q
current source
R
S
On/off
active-high
16
VCC
15
OFF
1 µA
10 µA
Boot
strap
In
14
13
R
S
Q
U.V.L.O.
Q
CB
PWM
comp.
Out
R
S
Q
Latch
S.C.P.
5
IN+
IN−
6
7
Error amp.
S.C.P.
comp.
17
AN8014S
Voltage regulators
■ Application Circuit Examples (continued)
3. DC-DC converter control (Example of polarity-inverting circuit)
In
Out
V1
Triangular
wave OSC
10
15
VREF
2.5V
Constant
CLM
VCC
Latch
current source
R
Q
S
On/off
active-high
16
OFF
1 µA
10 µA
Boot
strap
In
14 CB
R
Q
U.V.L.O.
Q
S
PWM
comp.
Out
13
R
S
Q
Latch
S.C.P.
5
IN+
IN−
6
7
V1
Error amp.
S.C.P.
comp.
1
VREF
18
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