ght=1 colspan=2>
APPLICATION MANUAL
GC3-I015B
Page 1
APPLICATION MANUAL
PWM switching regulator controller

IC
TK11840L
CONTENTS
1 . DESCRIPTION
2
2 . FEATURES
2
3 . APPLICATIONS
2
4 . PIN CONFIGURATION
2
5 . PACKAGE OUTLINE
2
6 . BLOCK DIAGRAM
3
7 . ABSOLUTE MAXIMUM RATINGS
4
8 . ELECTRICAL CHARACTERISTICS
5
9 . TEST CIRCUIT
6
10 . TYPICAL CHARACTERISTICS
6
11 . CIRCUIT DESCRIPTION
8
12 . APPLICATIONS INFORMATION
13
13 . NOTES
15
14. OFFICES
15
MEETING YOUR NEEDS TK11840L
GC3-I015B
Page 2
PWM switching regulator controller IC
TK11840L
1. DESCRIPTION
The TK11840L is a step-up DC-DC converter that drives
an external NPN power transistor using a constant
frequency PWM architecture.
The IC works with a wide operating supply range (1.8V
to 10V) and has an adjustable output.
The IC timing oscillator operating frequency is
programmable and can be set up to 1MHz.
The TK11840L incorporates a soft-start circuit, which
ensures that the output pulse width starts from 0 % duty
cycle and builds up to its proper level gradually when the
IC is first powered up.
The TK11840L also incorporates a short-circuit detection
function of a timer-latch type.
2. FEATURES
! Operation from 1.8V to 10V supply.
! Adjustable output voltage.
! High speed adjustable OSC. (Up to 1MHz)
!Incorporates a soft start circuit.
!Incorporates a short circuit detection of a timer-latch.
!Totem-pole type output in which current is adjustable
using an external resistor.(Pin 4)
!1
µ
A or less shutdown current.
!Low component count.
!Small 8 Pin SOT23L-8 package.
3. APPLICATIONS
!
White LED Backlighing and Frontlighting.
!
Step-up DC-DC Converters
!
Mobile Communication Systems:
Cellular Phone,PHS,DSC,PDA
!
Computer Peripherals Equipment
!
Battery Powered System
!
Portable Equipment
4. PIN CONFIGURATION
GND
1
2
3
4
8
7
6
5
BR/CTL
Vcc
SCP
EaIn
Out
OSC
FB
5. PACKAGE OUTLINE
!
SOT23L-8
Unit : mm
0.3
8
5
4
1
0.8
+0.10
-0.05
M
0.1
3.3
0.4
2.2
(0.
3
)
1.
2
0.
15
0~
0.
1
0.1
1.
4m
a
x
±0.2
±0
.1
+0
.
1
0
-0.
0
5
±0.3
±0.2
15
°m
a
x
3.4
±0.2 TK11840L
GC3-I015B
Page 3
6. BLOCK DIAGRAM
Pin No.
Symbol
Description
1
EaIn
Error amplifier inverting input
Feed back input. Threshold voltage is 0.5V . Connect resistive
divider tap to this pin.
2
SCP
Soft start and Short circuit detection
Connect external capacitor Cscp to this pin.
3
V
CC
Power Supply Voltage Input
4
BR/CTL
Output current setting and shutdown
5
Out
Totem-Pole type Output
Connect to base of external NPN switching transistor.
6
GND
Ground
7
OSC
Oscillation frequency setting pin
Connect external capacitor Ct and resistor Rt to this pin.
8
FB
Error amplifier output
Compensation pin for error amplifier. Connect capacitor Cfb
from FB pin (pin 8) to GND.
EaIn
FB
SCP
BR/CTL
GND
Out
OSC
8
2
7
6
1
3
4
5
Oscillator
PWM Comparator
Soft Start
Short Circuit Protection
Output Drive
Control Circuit
Reference
Voltage Supply
1.3V
0.5V
Error Amplifier
Vcc TK11840L
GC3-I015B
Page 4
7. ABSOLUTE MAXIMUM RATINGS
T
a
=25
°
C
Parameter
Symbol
Rating
Units
Conditions
Supply Voltage
V
CC
10
V
Power Dissipation
P
D
400
mW
*
Storage Temperature Range
T
stg
-55 ~ +150
°
C
Operating Temperature Range
T
OP
-40 ~ +85
°
C
Maximum Operating Frequency
f
MAX
~ 1000
kHz
Operating Voltage Range
V
OP
1.8 ~ 10
V
* P
D
must be decreased at rate of 3.2mW/
°
C for operation above 25
°
C. TK11840L
GC3-I015B
Page 5
8. ELECTRICAL CHARACTERISTICS
V
CC
=2V, T
a
=25
°
C
Value
Parameter
Symbol
MIN
TYP
MAX
Units
Conditions
Circuit to prevent malfunction
at low input voltage
Reset voltage
V
CC, Reset
-
-
0.9
V
Threshold voltage
V
CC, On
1.1
1.3
1.5
V
Soft start
Charging current
I
SS
-1.8
-1.2
-0.84
µ
A
V
SCP
=0V
Threshold voltage
V
SS, TH
0.65
0.75
0.85
V
Short circuit protection (S.C.P)
Charging current
I
SCP
-1.8
-1.2
-0.84
µ
A
V
SCP
=0V
Threshold voltage
V
SCP, TH
0.65
0.75
0.85
V
Oscillator
Frequency
f
OSC
440
550
660
kHz
Rt=3k , Ct=270pF
Frequency input stability
f
V
-
2
10
%
V
CC
=2.0V~10V
Frequency variation
with temperature
f
T
-
5
-
%
T
a
=-20
°
C~85
°
C
Error Amplifier
Threshold voltage
V
Ea
480
500
520
mV
V
FB
=0.45V
Line regulation
V
EaV
-
1
4
%
V
CC
=2.0V~10V
Variation with temperature
V
EaT
-
1
-
%
T
a
=-20
°
C~85
°
C
Input bias current
I
EaIn
-1.0
-0.2
1.0
µ
A
V
EaIn
=0V
Voltage gain
A
V
35.5
38.5
41.5
dB
Gain Band Width
GBW
-
6
-
MHz
A
V
=0dB
Output high voltage
V
EaOut, High
0.78
0.87
-
V
V
EaIn
=0V
Output low voltage
V
EaOut, Low
-
0.05
0.2
V
V
EaIn
=1.0V
Output source current
I
EaOut, Source
-
-40
-24
µ
A
V
FB
=0.45V
Output sink current
I
EaOut, Sink
24
40
-
µ
A
V
FB
=0.45V
Dead time control
Maximum duty cycle
D
MAX
65
75
85
%
Output driver
Output high voltage
V
Out, High
1.0
1.2
-
V
I
Out
=-15mA
Output low voltage
V
Out, Low
-
0.1
0.2
V
I
Out
=15mA
Output source current
I
Out, Source
-
-30
-20
mA
V
Out
=0.9V
Output sink current
I
Out, Sink
30
60
-
mA
V
Out
=0.3V
Pull-down resistor
R
Out
20
30
40
k Output drive control
Pin voltage
V
BR
0.25
0.35
0.45
V
R
BR
=620 Input off condition
I
BR, Off
-15
-
0
µ
A
Input on condition
I
BR, On
-
-
-45
µ
A
Pin current range
I
BR
-0.9
-
-0.1
mA
Entire device
On mode
I
CC, On
-
5.0
9.0
mA
R
BR
=620 Off mode
I
CC, Off
-
0.1
1.0
µ
A
BR/CTL Pin=V
CC
Supply
Current
Latch mode
I
CC, LT
-
5.3
9.5
mA
S.C.P. is operating TK11840L
GC3-I015B
Page 6
9. TEST CIRCUIT
2.0V
1
2
3
4
8
7
6
5
BR/CTL
Vcc
SCP
EaIn
Out
GND
OSC
FB
620 3k 270pF
1
µ
F
0.1
µ
F
TK11840L
10. TYPICAL CHARACTERISTICS
!
Supply current vs. Supply voltage (On mode)
T
a
=25
°
C, R
BR
=620 !
EaIn threshold voltage vs. Supply voltage
T
a
=25
°
C
0
2
4
6
8
10
0
2
4
6
8
10
Supply voltage V
CC
(V)
Supply current I
CC
(mA)
0
200
400
600
800
1000
0
2
4
6
8
10
Supply voltage V
CC
(V)
EaIn threshold voltage V
Ea
(mV)
!
EaIn threshold voltage variation ratio
vs. Supply voltage
T
a
=25
°
C
!
EaIn threshold voltage variation ratio vs. Ambient
temperature V
CC
=2.0V
-10.00
-5.00
0.00
5.00
10.00
0
2
4
6
8
10
Supply voltage V
CC
(V)
EaIn threshold variation ratio (%)
-10.00
-5.00
0.00
5.00
10.00
-20
0
20
40
60
80
100
EaIn threshold voltage variation ratio (%)
Ambient temperature T
a
(ºC) TK11840L
GC3-I015B
Page 7
!
Output source current vs. BR/CTL pin current
V
CC
=2.0V, T
a
=25
°
C
!
BR/CTL pin voltage vs. BR/CTL pin current
V
CC
=2.0V, T
a
=25
°
C
-50
-40
-30
-20
-10
0
-0.9
-0.7
-0.5
-0.3
-0.1
BR/CT L pin current I
BR
(mA)
Output source current I
Out
(mA)
0
100
200
300
400
500
600
-0.9
-0.7
-0.5
-0.3
-0.1
BR/CT L pin current I
BR
(mA)
BR/CTL pin voltage V
BR
(mV)
!
Oscillation frequency vs. Timing resistor
V
CC
=2.0V, T
a
=25
°
C
!
Frequency variation ratio vs. Supply voltage
Ct=270pF, Rt=3k , T
a
=25
°
C
10
100
1000
1
10
Timing resistor Rt (k )
Oscillation frequency fosc (kHz)
Ct=1000pF
Ct=3300pF
Ct=10000pF
Ct=270pF
Ct=100pF
-10.00
-5.00
0.00
5.00
10.00
0
2
4
6
8
10
Supply volt age V
CC
(V)
Frequency variation ratio (%)
!
Frequency variation ratio vs. Ambient temperature
V
CC
=2.0V, Ct=270pF, Rt=3k -10.00
-5.00
0.00
5.00
10.00
-20
0
20
40
60
80
100
Frequency variation ratio (%)
Ambient temperature T
a
(ºC) TK11840L
GC3-I015B
Page 8
11. CIRCUIT DESCRIPTION
12-1. Setting the output voltage
To obtain a regulated output voltage for most common
step-up regulator applications, connect a voltage-divider
from the output (Vout) to EaIn. (See Fig1)
The output voltage is determined by the 0.5V reference
level and by the selection of two external resistors
according to the equation.




+
×
=
1
R
2
R
1
V
Vout
f
Re
where V
Ref
=0.5V
The input bias current of EaIn has -0.2
µ
A.typical .
Error amplifier
V
Ref
=0.5V
1
Vout
EaIn
R2
R1
Fig1: Setting the output voltage
12-2. Shutdown
To disable the device (shutdown mode), set BR/CTL Pin
(Pin 4) open or connect to V
CC
as shown in Fig 2.
During shutdown, the supply current of the IC drops to
1
µ
A or less.
4 BR/CTL
Rb
Fig2: Shutdown TK11840L
GC3-I015B
Page 9
12-3. Sawtooth wave Oscillator
The oscillator operates by rapidly charging an external
capacitor Ct and resistor Rt with a current from a lower
threshold voltage V
OSC,L
to an upper threshold voltage
V
OSC,H
.
Once the Ct voltage reaches the upper threshold voltage,
the capacitor is slowly discharged back through resistor
Rt to the lower threshold voltage.
The oscillator frequency can be expressed as
Rise
L
,
OSC
H
,
OSC
OSC
t
V
V
ln
Rt
Ct
1
f
+ where V
OSC,H
=800mV
V
OSC,L
=100mV
t
Rise
=0.1
µ
Sec
This equation is rough estimate, because it takes no
account of overshoot around the upper threshold level
when Ct is charged rapidly.
A plot of OSC frequency vs. Rt and Ct is shown in Fig 3.
10
100
1000
1
10
Timing resistor Rt (k )
Oscillation frequency fosc (kHz)
Ct=1000pF
Ct=3300pF
Ct=10000pF
Ct=270pF
Ct=100pF
Fig.3: Oscillator frequency vs. Timing resistor
7
OSC
Rt
Ct
Fig 4. Oscillator pin connection
V
OSC,H
800mV
V
OSC,L
100mV
Fall Time
Rise Time


* t
Rise
=0.1
µ
Sec
Fig 5. Oscillator waveform TK11840L
GC3-I015B
Page 10
12-4. Setting the output source current
The TK11840L is designed to drive an external bipolar
NPN switching transistor, enabling high efficiency
conversion with low input voltages.
The output current which is a base current of the NPN
switching transistor is set by a resistor Rb at pin4.
This function ensures optimum efficiency over a wider
range of load currents.