AN8011S [PANASONIC]
2-channel step-down, step-up, or inverting use DC-DC converter control IC; 双通道降压，升压或反相使用DC-DC转换器控制IC
| 型号： | AN8011S |
| 厂家： | 
PANASONIC |
| 描述： | 2-channel step-down, step-up, or inverting use DC-DC converter control IC |
| 文件： | 总16页 (文件大小：162K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Voltage Regulators
AN8011S
2-channel step-down, step-up, or inverting use
DC-DC converter control IC
Unit: mm
■ Overview
10.1±0.3
16
9
The AN8011S is a DC-DC converter control IC
with two-channel output using the PWM method
which allows 500 kHz high-speed control.
Respecitve output operation can be completely
synchronized with each other by using the same
oscillation output.
(0° to 10°)
0.3
1
8
■ Features
• PWM control frequency of 500 kHz is available.
• Wide operating supply voltage range
(VCC = 3.6 V to 34 V)
• Built-in 2-channel of open collector type for out-
put (A single-channel is also usable for inverted
amplification type)
1.27
(0.605)
0.40±0.25
Seating plane
Seating plane
SOP016-P-0225A
• Each output can be stopped independently by the
external control .
• Built-in on/off function for the operation/stop of IC Incorporating circuit for short-circuit portection and under-
voltage lock-out (U.V.L.O.)
• The latch circuit is externally controllable.
• Low consumption current (during operation: 5 mA, during standby: 2 µA)
■ Applications
• LCD displays, digital still cameras, and PDAs
■ Block Diagram
Error amp.
Latch
VREF
PWM1
Unlatch pro.
Short pro.
U.V.L.O.
OSC
Unlatch pro.
PWM2
On/
Off
Error amp.
1
AN8011S
Voltage Regulators
■ Pin Descriptions
Pin No.
Symbol
Description
1
CT
Pin for connecting the oscillation frequency setting capacitor for triangular oscillation
circuit. Frequecy of triangular oscillation is set by connecting a capacitor between this
terminal and GND.
2
RT
Resistor connection pin for setting the oscillation frequency of triangular oscillation
circuit. Frequecy of triangular oscillation is set by connecting resistance between the
pin and GND
3
4
5
On/Off
IN−2
"On/Off" pin for turning on/off IC. "Low" stops IC (output off) and "High" operates IC.
Inverted input pin for channel 2 error amplifier
F/B 2
Output pin for channel 2 error amplifier. Gain setting or phase compensation is per-
formed by connecting resistor or capacitor between the pin and IN−2. It is also connected
to PWM short-circuit protecion.
6
DTC 2
Pin for setting dead-time period of channel 2. The dead-time of channel 2 is set by
connecting external resistor. Soft start function can be also given by connecting capaci-
tor in parallel with the external resistor. In addition, only channel 2 output can be turned
off by decreasing the pin voltage to below 0.12 V. (short-circuit protection function stop
circuit)
7
8
Out 2
GND
VCC
Channel 2 open-collector type output pin. IO = 100 mA maximum
Grounding pin of signal system.
9
Power supply voltage application pin. It detects start voltage and stop voltages
Channel 1 open-collector type output pin. IO = 100 mA maximum
10
11
Out 1
DTC 1
Pin for setting dead-time period of channel 1. The dead-time period of channel 1 is set
by connecting external resistor. Soft start function can be also given by connecting capacitor
in parallel with the external resistor. In addition, only channel 1 output can be turned off
by decreasing the pin voltage to below 0.12 V. (short-circuit protection function stop
circuit)
12
F/B 1
Output pin for channel 1 error amplifier. Gain setting or phase compensation is per
formed by connecting resistor or capacitor between the pin and IN−1. It is also con
nected to PWM short-circuit protection.
13
14
15
IN−1
IN+
Inverted input pin for channel 1 error amplifier.
Pin for noninverted input of channel 1error amplifier.
Latch
Pin for connecting the time constant setting capacitor for timer latch type short-circuit
protection circuit. The time constant for short-circuit protection is set by connecting
a capacitor between this terminal and GND.
16
VREF
Internal reference voltage output pin (2.5 V(allowance: ±3%)). If a load of 20 mA typical
or more is applied, the overcurrent protection operates to reduce VREF and switching
operation stops.
2
Voltage Regulators
AN8011S
■ Absolute Maximum Ratings at Ta = 25°C
Parameter
Supply voltage
Symbol
VCC
PD
Rating
35
Unit
V
Power dissipation *
380
mW
°C
Operating ambient temperature
Storage temperature
Topr
−30 to +85
−40 to +125
Tstg
°C
Note) 1. Do not apply ecternal currents or voltages to any pins not speifically mentioned.
For circuit currents, '+' denotes current flowing into the IC, and '−' denotes current flowing out of the IC.
2
: When using the IC at T of 25°C or more, the power dessipation should be decreased 3.8 mW per 1°C.
a
*
■ Recommended Operating Range
Parameter
Supply voltage
Symbol
VCC
Range
Unit
3.6 to 34
V
■ Electrical Characteristics at VCC = 12 V, Ta = 25°C
Parameter
Reference voltage block
Output voltage
Symbol
Conditions
Min
Typ Max Unit
VREF
2.413 2.5 2.588
V
Input regulation with input fluctuation Line
VCC = 3.6 V to 34 V
3
2
20
10
mV
mV
%
Load regulation
Load IREF = 0 mA to 5 mA
Output voltage temperature
characteristics 1 *
VTC1
VTC2
ICC
Ta = −25°C to + 25°C
Ta = 25°C to 85°C
±1
Output voltage temperature
characteristics 2 *
±1
%
Overcurrent protection drive current *
U.V.L.O. block
−20
mA
Circuit operation start voltage
Hysteresis width
VUON
VHYS
2.8
3.1
3.4
V
100
200
300
mV
Error amplifier block 1
Input offset voltage 1
VIN-O1
IB1
−6
6
mV
nA
V
Input current 1
−500 −25
0.5
100
0.8
Common-mode input voltage range
High-level output voltage 1
Low-level output voltage 1
Error amplifier block 2
Input current 2
VCM
VEH1
VEL1
VREF −0.3
V
0.5
V
IB2
25
100
nA
V
Common mode input threshold voltage
High-level output voltage 2
Low-level output voltage 2
VIN+
VEH2
VEL2
0.72 0.75 0.78
VREF −0.3
V
0.5
V
3
AN8011S
Voltage Regulators
■ Electrical Characteristics(continued) at VCC = 12 V, Ta = 25°C
Parameter
PWM comparator 1/2 block
High-level input threshold voltage
Low-level input threshold voltage
Input current
Symbol
Conditions
Min
Typ Max Unit
VDT-H fOSC = 200 kHz, duty = 100%
VDT-L fOSC = 200 kHz, duty = 100%
1.2
V
0.6
V
IDTC
RT = 20 kΩ
−37
−34
−31
µA
Output 1/2 block
Output frequency 1
fOUT1
fdv
CT = 150 pF, RT = 20 kΩ, IO = 30 mA 180
200
220
2
kHz
%
Frequency 1
VCC = 3.6 V to 34 V
−2
CT = 150 pF, RT = 20 kΩ
Output duty ratio 1
Du1
Du2
CT = 150 pF, RT = 20 kΩ, RDTC = 24 kΩ
CT = 150 pF, RT = 20 kΩ, RDTC = 33 kΩ
40
65
45
75
50
85
%
%
Output duty ratio 2
Output saturation voltage 1
Output saturation voltage 2
Output leak current 1
VO(sat)1 IO = 30 mA
VO(sat)2 IO = 100 mA
0.9
1.2
10
V
V
IOLe1
VCC = 34 V, when output
µA
transistor is off
Frequency temperature characteristics 1 *
Frequency temperature characteristics 2 *
Output frequency 2*
fdT1
fdT2
fOUT2
fdv2
fOSC = 200 kHz, Ta = −30°C to +25°C
fOSC = 200 kHz, Ta = 25°C to 85°C
CT = 150 pF, RT = 6.6 kΩ, IO = 30 mA
±9
±9
%
%
500
±2
kHz
%
Frequency 2*
VCC = 3.6V to 34V,
CT = 150 pF, RT = 6.6 kΩ
Short-circuit protection block
Input threshold voltage
Latch drive voltage
VSLTH
VSLON
ICHG
1.75 1.85 1.95
1.15 1.25 1.35
V
V
Charge current
−120 −50
−40
µA
Unlatch pro. 1/2 block
Input threshold voltage
On/off block
VULTH
0.12
0.8
5
V
V
Threshold voltage
VTH
2
Whole device
Total consumption current
Total consumption current fluctuation
Standby consumption current
ICC
VCC = 12 V, RT = 20 kΩ
7
2
2
5
mA
mA
µA
µA
ICC(max.) VCC = 3.6 V to 34 V, RT = 20 kΩ
ICC(SB) VCC = 12 V, VREF is down
Maximum standby consumption current ICC(SB-M) VCC = 34 V, VREF is down
Note) : These characteristics are theoretical values based on the IC design and are not guaranteed.
*
4
Voltage Regulators
AN8011S
■ Terminal Equivalent Circuits
Pin No.
Equivalent circuit
Description
I/O
1
CT:
O
VREF
The terminal used for connecting a timing
capacitor to set oscillator frequency. Use a
capacitance value within the range of 100 pF
to 0.1mF. For frequency setting method, re-
fer to the "Application Notes, [2] Function
descriptions" section. Use the oscillation fre-
quency in the range of 1 kHz to 500 kHz.
16
To PWM input
IO
CT
1
OSC
comp.
2IO
2
RT:
I
VREF
16
The terminal used for connecting a timing
resistor to set oscillattion frequency.
Use a resistance value ranging from 5.1 kΩ
to 20 kΩ.
The terminal voltage is 0.67 V typ.
OSC PWM
RT (= 0.67 V)
2
3
On/Off:
I
The terminal for on/off control.
High-level input: normal operation
(VON/OFF > 2.0 V typ.)
Internal
circuit start/stop
On/Off
3
17 kΩ
Low-level input: standby state
(VON/OFF < 0.8 V typ.)
13 kΩ
The total current consumption in the standby
state can be suppressed to a value below 5 µA.
4
IN−2:
I
VREF
The terminal for the inverted input of ch.2
error amplifier. Use a common-mode input
ranging from − 0.1 V to 0.8 V.
16
0.75 V
4
IN−2
5
AN8011S
Voltage Regulators
■ Terminal Equivalent Circuits (continued)
Pin No.
Equivalent circuit
Description
I/O
5
FB2:
O
VREF
16
The output terminal of ch.2 error amplifier.
Its source current is −25 µA typ. and sink
current is 8 mA typ.
25 µA typ.
PWM2
CT
Correct the frequency characteristics of the
gain and the phase by connecting a resistor
and a capacitor between the terminal and
IN−2 terminal.
8 mA
typ.
5 FB2
6
DTC2:
I
1) Terminal for connecting a resistor and a
capacitor for setting the dead-time and the
soft start period of ch.2 PWM output.
Input current IDTC is determined by the tim-
ing resistor RT so that dispersion, and fluc-
tuation with temperature are suppressed. The
input current is −35 µA typ.
VREF
16
IDTC2
PWM2
CT
U.V.L.O.
output
when RT = 20 kΩ
VRT
IDTC2
=
× 1.04 (A)
RT
6 DTC2
(VRT: 0.67 V typ.)
2) The ch.2 output can be turned off by reduc-
ing the terminal voltage to below 0.12 V.
(short-circuit protection function stop)
7
Out2:
O
VREF
16
The ch.2 open-collector type (Darlington)
output terminal.
Out2
7
The absolute maximum rating of ouput cur-
rent is 150 mA.
Use with an output current under 100 mA
normally.
8
9
GND:
GND pin
8
GND
VCC
:
9
The pin to which supply voltage is applied.
Use within an operating supply voltage range
of 3.6 V to 34 V.
VCC
6
Voltage Regulators
AN8011S
■ Terminal Equivalent Circuits (continued)
Pin No.
Equivalent circuit
Description
I/O
10
Out1:
O
VREF
16
Out1
10
The ch.1 open collector type (darlington)
output terminal.
The absolute maximum rating of output cur-
rent is 150 mA.
Use with an output current of 100 mA or less
normally.
11
DTC1:
I
1) Terminal for connecting a resistor and a
capacitor for setting the dead-time and the soft
start period of ch.1 PWM output.
Input current IDTC is determined by the tim-
ing resistor RT so that dispersion and fluctu-
ation with temperature are suppressed. The
input current is −35 µA typ, when RT = 20 kΩ.
VRT
VREF
16
IDTC1
PWM1
CT
U.V.L.O.
output
IDTC2
=
× 1.04 (A)
RT
(VRT: 0.67 V typ.)
11 DTC1
2) The ch.1 output can be turned off by reduc-
ing the terminal voltage to below 0.12 V.
(short-circuit protection function stop)
12
FB1:
O
VREF
16
The output terminal of ch.1 error amplifier.
Its source current is −25 µA typ. and sink
current is 8 mA typ.
25 µA typ.
PWM1
CT
Correct the frequency characteristics of the
gain and the phase by connecting a resistor
and a capacitor between the terminal and
IN−1 terminal.
8 mA
typ.
12 FB1
13
14
IN−1:
I
I
VREF
The terminal for the inverted input of ch.1
error amplifier. Use a common-mode input
ranging from − 0.1 V to +0.8 V.
IN+:
The terminal for noninverted input of ch.1
error amplifier. Use a common-mode input
ranging from − 0.1 V to +0.8 V.
13
14
IN − 1
IN +
7
AN8011S
Voltage Regulators
■ Terminal Equivalent Circuits (continued)
Pin No.
Equivalent circuit
Description
I/O
15
Latch:
O
VREF
Terminal for connecting the time constant
setting capacitor for timer latch short-circuit
protection circuit. The charge current ICHG is
about −80 µA.
16
ICHG
4.2 kΩ
Latch
typ.
S
Q
R
1.25 V
typ.
30 kΩ
typ.
10kΩ
typ.
1.25 V
typ.
15
Latch
16
VREF
:
O
VCC
9
The output terminal for the reference voltage
(2.5 V typ.).
VREF overcurrent
detection
Use it with a load current of −1 mA or under.
The terminal has a built-in short-circuit pro-
tection circuit, and the short-circuit current
is −20 mA typ.
Bias to
other blocks
Use the terminal for setting the reference in-
put of the error amplifier.
VREF
16
8
Voltage Regulators
AN8011S
■ Application Notes
[1] Main characteristics
Reference voltage temperature characteristics
Maximum duty ratio temperature characteristics
2.500
54
53
52
51
50
49
2.495
2.490
2.485
2.480
−20
0
20
40
60
80
−20
0
20
40
60
80
−40
100
−40
100
Ambient temperature Ta (°C)
Ambient temperature Ta (°C)
Output frequency temperature characteristics
DTC pin voltage
Output duty ratio
210
100
90
80
70
60
50
40
30
20
10
0
209
208
207
206
205
204
203
202
201
200
fOUT = 500 kΩ
fOUT = 200 kΩ
−20
0
20
40
60
80
−40
100
0
0.5
1
1.5
Ambient temperature Ta (°C)
DTC pin voltage (V)
Output frequency characteristics
500
100
RT = 10 kΩ
RT = 5.1 kΩ
RT = 20 kΩ
10
0
102
103
104
105
CT (pF)
9
AN8011S
Voltage Regulators
■ Application Notes (continued)
[2] Function descriptions
1. Reference voltage block
This block is composed of the band gap circuit, and outputs the temperature compensated 2.5 V reference
voltage to the VREF terminal. The reference voltage is stabilized when the supply voltage is 3.6 V or higher, and
used as the operating power supply for the IC inside. It is possible to take out a load current of up to −3 mA. Also,
an overcurrent portection circuit is built in for the load, thereby protecting the IC from destruction when VREF
terminal is short circuited.
2. Triangular wave oscillation block
The triangular wave which swings from the wave peak of approximately 1.4 V to the wave bottom of
approximately 0.4 V will be generated by connecting a timing capacitor and a resistor to the CT terminal and RT
terminal respectively. The oscillation frequency can be freely decided by the value of CT and RT connected
externally. The triagular wave is connected with the inverted input of PWM comparator of the IC inside.
3. Error amplifier block
This block detects the output voltage of DC-DC conveter, and inputs the signal amplified by the PNP transistor
input type differential amplifier to the PWM comparator.
The common-mode input voltage range is − 0.1 V to 0.8 V, and is a voltage obtained by dividing the reference
voltage with resistors.
Also, it is possible to perform the gain setting and the phase compensation arbitrarily by connecting the
feedback resistor and the capacitor from the error amplifier output terminal to the inverted input terminal.
The output voltage VOUT, if positive, is obtained by connecting the resistor-divided reference voltage to the
noninverted input terminal as shown in figure 1. 1), and the output voltage VOUT, if negative, is obtained by
connecting to the inverted input terminal as shown in figure 1. 2). The output voltages in each of these cases are
given in the following equations.
R1 + R2
R2
R1 + R2
R2
R3 + R4
R3
V
OUT1 = VIN
×
×
V
OUT1 = − (VREF − VIN-1 ) ×
+ VREF
R2
VIN+ = VREF
VIN−1 = VREF
×
R1 + R2
VOUT1 VREF
VREF
16
16
R1 R3
R1 R3
IN+
Error amp.1
Error amp.1
PWM comparator
input
PWM comparator
input
IN+
14
14
IN−1
13
IN−1
13
12
12
R2 R4
R2 R4
RNF
RNF
FB1
FB1
VOUT1
CNF
1) Positive output
CNF
2) Negative output
Figure 1. Connection method of error amplifier 1
FB2
The output voltage of channel 2 VOUT2 is
5
4
VOUT2
R1
VREF: 2.5 V
exclusively for positive voltage ouput, and
method of connection is as shown in figure 2.
R1 + R2
R3
Error amp.2
PWM comparator input
V
OUT2 = 0.75 ×
0.75V
R2
IN−2
R4
R2
Figure 2. Cnnection method of error amplifier 2
10
Voltage Regulators
AN8011S
■ Application Notes (continued)
[2] Function descriptions (continued)
4. Timer latch short-circuit protection circuit
This circuit protects the external main swiching devices, switching diodes, choke coils, and etc. from
destruction or deterioration if overload or short-circuit of power supply output lasts for a certain time.
The timer latch type short-circuit protection circuit detects the output level of each error amplifier, and when
the ouput level of either one or both of the error amplifiers exceeds 1.85 V typical, the timer circuit is actuated, and
initiates charging the external capacitor for protection enable.
If the ouput of the error amplifier does not return to a normal voltage range by the time when the voltage of
this capacitor reaches 1.25 V, it sets the latch circuit, cuts off the ouput drive transistor, and sets the dead time to
100%.
5. Low input voltage malfunction prevention circuit (U.V.L.O.)
This circuit protects the system from destruction or deterioration due to control malfunction caused by the
supply voltage reduction in the transient state of power on or off.
The low input voltage malfunction prevention circuit detects the internal reference voltage according to the
supply voltage level, and cuts off the output drive transistor by resetting the latch circuit, thereby setting the dead-
time to 100% and keeping the latch terminal low.
6. PWM comparator block
The PWM comparators, each has one inverted input, and two noninverted inputs, and controls the on-period
of output pulse in accordance with the input voltage. It turns on the output transistor during the period when the
triangular wave of CT terminal is lower than either the error amplifier ouput voltage or the DTC terminal voltage.
The dead-time is set by the addition of a resistor between the DTC terminal and GND. By the addition of a
capacitor in parallel with the external resistor RDTC, the soft start function which gradually extends the on-period
of the ouput pulse by the RC time constant when the power supply is turned on starts to work.
7. Output block
The ouput drive transistor is of open-collector type output connected in Darlington circuit of emitter common
GND. The breakdown voltage of the collector ouput terminal is 34 V and it is possible to obtain up to 100 mA
ouput current.
8. Remote circuit
It is possible to switch on/off the IC control by an external control signal. When the on/off terminal voltage is
lowered to a value below approximately 0.8 V, the internal reference voltage goes down, thereby the IC control
is stopped and the circuit current is decreased to 5 µA or less. When the on/off terminal voltage is increased to a
value higher than approximately 2.0 V, the internal reference voltage raises and the control operation is started.
[3] The time constant setting method for timer latch type short-circuit protection circuit
Figure 3 shows the block diagram of the protection latch circuit. The comparator for short-circuit protection
compares the output voltage of error amplifier VFB with the reference voltage (1.85 V) at all the time. When the load
conditions of DC-DC converter output is stabilized, there is no fluctuation of error amplifier output, and the short-
circuit protection comparator also keeps the balance. At this moment, the switch SW1 will be in the off state, and the
latch terminal voltage will be kept at approximately 0.9 V typical.
When the load conditions suddenly change, and high-level signal (1.85 V typical of higher) is inputted from the
error amplifier to the noninverted input of the short-circuit protection comparator, the short-circuit protection com-
parator outputs the high-level signal. This signal turns on the switch SW1, and the charging to the capacitor CS
connected externally to the latch terminal is started with a current of 80 µA typical.
When the external capacitor CS is charged up to approximately 1.25 V typical, the latch circuit is set and the under-
voltage lock-out circuit (U.V.L.O.) is enabled, thereby the ouput drive transistor is cut off and the dead-time is set to
100%.
Once the under-voltage lock-out circuit (U.V.L.O.) is enabled, the latch circuit will not be reset unless the power
supply is switched off.
11
AN8011S
Voltage Regulators
■ Application Notes (continued)
[3] The time constant setting method for timer latch type short-circuit protection circuit (continued)
VREF
ICHG
80 µA typ.
5
SW1
FB2
FB1
Latch comp.
4.2 kΩ typ.
12
30 kΩ
typ.
Cut output off
S
R
R
1.25 V
typ.
1.85 V
Latch
U.V.L.O.
10 kΩ
typ.
4
Latch
CS
Figure 3. Short-circuit protection circuit
When the power supply is turned on, the output is considered to be short-circuited state, so that the error amplifier
output becomes high-level, then SW1 becomes on state and the charging starts. It is necessary to set the external
capacitor so as to start up the DC-DC converter output voltage before setting the latch circuit in the later stage.
Especially, pay attention to the delay of the start-up time when applying the soft-start.
[4] Explanation of unlatch protection circuit operation
Figure 4 shows the block diagram of the unlatch protection circuit. It is possible to suppress FB terminal, the error
amplifier output terminal of the channel, to low by setting DTC terminal to 0.12 V or less through external signal.
Consequently, by controlling the DTC terminal voltage, it is possible to operate only one channel, or to start and stop
each channel in any required sequence.
FB1 12
5 FB2
Error amp.1
Error amp.2
To PW1
To PW2
IN+
14
13
4
IN−2
IN−1
IDTC1
IDTC2
11
6
DTC1
DTC2
Unlatch protection
comp.1
Unlatch protection
comp.2
0.12 V typ.
0.12 V typ.
Figure 4. Unlatch protection circuit
12
Voltage Regulators
AN8011S
■ Application Notes (continued)
[5] Triangular wave oscillation circuit
• Oscillation frequency setting method
The waveform of triangular wave oscillation is obtained by charging and discharging of the constant current IO
from the external timing capacitor CT which is connected to CT terminal. The constant current is set by the externally
attached timing resistor RT .
The peak value of the wave VCTH and the trough
value of the wave VCTL are fixed at approximately 1.4 V
typical and 0.4 V typical respectively.
VCTH
= 1.4 V typ.
The oscillation frequency fOSC is obtained by the
following formula;
VCTL
= 0.4 V typ.
t1
t2
1
IO
fOSC
(typ.)
=
=
Charging Discharging
t1 + t2
2 × CT × (VCTH − VCHL)
VRT
RT
0.67
RT
Where IO = 2 ×
= 2 ×
T
Because VCTH − VCTL = 1V
0.67
CT × RT
Figure 5. Triangular wave oscillation waveform
fOSC
(typ.)
=
[Hz]
The ouput frequency fOUT is equal to fOSC since it is PWM-controlled.
[6] Dead-time (maximum duty) setting method
The setting of the dead-time is conducted by adjusting the DTC terminal voltage VDTC as shown in figure 6. Since
the DTC terminal provides a constant current output through the resistor RT, VDTC is adjusted by attaching the external
resistor RDTC
.
The output duty ratio Du and the DTC terminal voltage VDTC are expressed by the following formula. When the
oscillation frequency fOSC is 200 kHz, the output duty ratio is 0% at VDTC = 0.42 V, and 100% at VDTC = 1.35 V.
Pay attention to the peak volue and the trough value of triangular wave because the overshoot and undershoot
voltages depend on the frequency.
VREF
CT waveform
VCTH
VDTC
VCTL
VRT
RT
IDTC
=
× 1.04 [A]
DTC waveform
IDTC
PWM
CT
FB
tOFF
Off
tON
On
Out waveform
Du
Off
DTC
RDTC
tON
tON + tOFF
=
=
×
100 [%]
CDTC
(typ.)
VCTH −VDTC
VCTH −VCTL
×
100 [%]
ex.) When fOSC = 200 kHz (RT = 20 kΩ, CT = 150 pF),
VDTC = IDTC × RDTC
VCTH ≈ 1.4 V(typ.)
VRT ≈ 0.67 V(typ.)
IDTL ≈ 35 µA (typ.)
(typ.)
RDTC
VCTL ≈ 0.4 V(typ.)
= VRT
×
× 1.04 [V]
RT
Figure 6. Dead-time setting method
When the capacitor CDTC is added in parallel with the external resistor RDTC, the soft start function gradually extends
the on-period of the output pulse when the power supply is turned on. This prevents the overshoot of the DC-DC
converter output.
13
AN8011S
Voltage Regulators
■ Application Notes (continued)
[7] Timing chart
Supply voltage (VCC
)
3.6 V
2.5 V
3.1 V typ.
Lock-out release
Reference voltage (VREF
)
Error amplifier output (FB)
1.83 V
Power supply
Latch terminal voltage
Triangular wave (CT)
on
1.3 V
0.9 V
0.40 V
0.03 V
High
Dead-time voltage (VDT
)
Low
Output transistor collector
waveform(OUT)
Soft start operation
Maximum duty
Figure 7. Operation waveform of PWM comparator
2.5 V
Reference voltage (VREF
)
Short-circuit protection input threshold level
Comparator threshold level
1.85 V
1.4 V
0.9 V
DTC terminal voltage
Latch terminal voltage
Error amplifier ouput (FB)
0.40 V
Triangular wave (CT)
High
Output transistor collector waveform
(OUT)
Low
High
Short-circuit protection comparator
output
tPE
Low
Figure 8. Operation waveform of short-circuit protection
14
Voltage Regulators
AN8011S
■ Application Circuit Examples
• Application circuit example 1
SBD
23 kΩ
3 V
−5 V
7 kΩ
0.01 µF
120 kΩ
VCC
7
SBD
3 V
5 V
f = 200 kHz
Duty = 75%
Error
amp.
25.5 kΩ
Latch
VREF
PWM1
PWM2
Unlatch pro.
4.5 kΩ
Short pro.
U.V.L.O.
OSC
To pin 4
Unlatch pro.
On/
Off
Error
amp.
120 kΩ
0.01 µF
SBD
5V
3 V
25.5 kΩ
4.5 kΩ
15
AN8011S
Voltage Regulators
■ Application Circuit Examples
• Application circuit example 2
500 Ω
VIN = 7 V
3.3 V
0.01 µF
100 Ω
VCC = 7 V
120 kΩ
2.5 V
10 µF
Error
amp.
Latch
VREF
PWM1
Unlatch pro.
Short pro.
U.V.L.O.
OSC
Unlatch pro.
PWM2
On/
Off
Error
amp.
120 kΩ
0.01 µF
R
500 Ω
VCC = 7 V
5 V
25.5 kΩ
0.75 V
4.5 kΩ
16
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