TX4139
2A, 75V, 200KHz Step-Down Converter
DESCRIPTION
The TX4139 is a monolithic step-down
switch mode converter. It achieves 2A
continuous output current over a wide input
supply range with excellent load and line
regulation.
The maximum peak current can be
programmed by sensing current through an
accurate sense resistor.
Fault
condition
protection
includes
cycle-by-cycle current limiting and thermal
shutdown.
The TX4139 requires a minimum number of
readilyavailable standard external components.
TheTX4139 is available in 8-pin ESOIC8
packages.
FEATURES
Wide 4.5V to 75V Operating Input Range
Output Adjustable from 0.8V to 50V
Light load High Efficiency
Power Save Mode at light load
Programmable maximum peak current
130mΩ
Internal Power MOSFET Switch
91.8% Efficiency at Vin=72V，Vout=12V@1.2A
81.4% Efficiency at Vin=72V，Vout=5V@0.8A
Fixed 200KHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Available in 8-Pin ESOIC8 Packages
APPLICATIONS
Balance Bike
ebike
USB Power Supplies
TYPICAL APPLICATION
R3
10Ω
C3
100nF
3
C1A
10 µF
0
100V
VIN
ILIM
BS
8
C1B
2
R4
0.1µF
30mΩ
100V
6
TX4139
EN
SW
1
D1
SS310
5V/2A
L1
33µΗ
ILIM(9)
C4
47pF
R1
300K
1%
R2
57.1K
1%
C2
22 µF
0
16V
POK
7
GND
4
FB 5
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ORDERING INFORMATION
PART NUMBER
ETEMPERATURE
RANGE
PACKAGE
TX4139
-40°C to 85°C
ESOIC8
ABSOLUTE MAXIMUM RATINGS
(1)
Supply Voltage V
IN
,V
ILIM .............................................................
76V
V
SW .............................................................................
-0.3V to V
IN
+ 0.3V
V
BST.............................................................................................
V
SW
+ 6.0V
V
POK .................................................................................................
0V to 45V
All Other Pins .....................................-0.3V to +6.5V
Junction Temperature ..................................... 150°C
Lead Temperature ........................................... 260°C
Storage Temperature ...................... -65°C to +150°C
PIN CONFIGURATION
Recommended Operating Conditions
(2)
SW
ILIM
VIN
GND
1
2
3
4
ILIM
(9)
8
7
6
5
BS
POK
EN
FB
Supply Voltage V
IN..........................................................
4.5V to 75V
Output Voltage V
OUT
0.8V to 40V
Operating Temperature ..................... -40°C to +85°C
Thermal Resistance
(3)
θ
JA
θ
JC
ESOIC8 .................................... 45 ......... 15 ...
°C/W
Notes:
1) Exceeding these ratings may damage the device.
2) The device is not guaranteed to function outside of its operating conditions.
3) Measured on approximately 42x45mm^2 of 1 oz copper.
PIN No.
1
2、9
3
PIN
NAME
SW
ILIM
VIN
PIN DESCRIPTION
Switch Output. Connect this pin to the switching end of the inductor.
programmable maximum peak current pin by sensing current through an
accurate sense resistor between this pin and VIN.
Supply Voltage. The TX4139 operates from a +4.5V to +75V unregulated input.C
IN
is needed to prevent large voltage spikes from appearing at the input. Put C
IN
as
close to the IC as possible. It is the drain of the internal power device and power
supply for the whole chip.
Ground. This pin is the voltage reference for the regulated output voltage. For this
reason care must be taken in its layout. This node should be placed outside of the
D1 to C
IN
ground path to prevent switching current spikes from inducing voltage
noise into the part.
Feedback. An external resistor divider from the output to GND, tapped to the FB
pin sets the output voltage. To prevent current limit run away during a short circuit
fault condition the frequency-fold-back comparator lowers the oscillator frequency
when the FB voltage is below 250mV.
Enable pin. Connect to low off the chip,Floating is enable
Power good signal. When FB is less than 90% of 0.8V, PGOOD is low. It is an
open-drain output. Use a high value pull-up resistor externally to pull it up to
system power supply or its output as next chip enable signal. connected to Gnd or
floating when don’t use this function.
Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver.
Connect a 100nF ceramic cap and 10ohm resistor between this pin and SW.
4
Gnd
5
FB
6
7
EN
POK
8
BS
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ELECTRICAL CHARACTERISTICS
V
IN
= 12V, T
A
= +25°C, unless otherwise noted.
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Feedback Voltage
Feedback Bias Current
Switch On Resistance
Current Limit (4)
Oscillator Frequency
Fold-Back Frequency
Boot-Strap Voltage
Minimum On Time (5)
Under Voltage Lockout Threshold Rising
Under Voltage Lockout Threshold Hysteresis
Supply Current (Quiescent)
Thermal Shutdown (5)
Note:
4)
sense resistor defined
5)
Guaranteed by design
V
FB
I
BIAS(FB)
R
DS(ON)
4.5V
≤
V
IN
≤
80V
V
FB
= 0.8V
0.785
0.805
10
130
0.825 V
nA
mΩ
1.5
A
KHz
V
ns
3.6 V
mV
700
μA
°C
240 KHz
1.2
f
SW
V
BST
- V
SW
t
ON
V
FB
= 1V
3.0
200
V
EN
=
2V, V
FB
= 1V
V
FB
= 0.6V
V
FB
= 0V
160
1.35
200
70
6
100
3.3
400
160
OPERATION
Main Control Loop
The TX4139 is a current mode buck regulator.
That is, the error amplifier (EA) output voltage is
proportional to the peak inductor current. At the
beginning of a cycle, the integrated high side power
switch M1 is off; the EA output voltage is higher than
the current sense amplifier output; and the current
comparator’s output is low. The rising edge of the
200KHz clock signal sets the RS Flip-Flop. Its output
turns on M1 thus connecting the SW pin and inductor
to the input supply.
The increasing inductor current is sensed and
amplified by the Current Sense Amplifier. Ramp
compensation is added to Current Sense Amplifier
output and compared to the Error Amplifier output by
the PWM Comparator. When the Current Sense
Amplifier plus Slope Compensation signal exceeds
the EA output voltage, the RS Flip-Flop is reset and
the TX4139 reverts to its initial M1 off state. If the
Current Sense Amplifier plus Slope Compensation
signal does not exceed the COMP voltage, then the
falling edge of the CLK resets the Flip-Flop. The
output of the Error Amplifier integrates the voltage
difference between the feedback and the 0.8V
bandgap reference. The polarity is such that a FB pin
voltage lower than 0.8V increases the EA output
voltage. Since the EA output voltage is proportional
to the peak inductor current, an increase in its voltage
increases current delivered to the output. An external
Schottky Diode (D1) carries the inductor current
when internal power MOS is off.
APPLICATION INFORMATION
Setting the Output Voltage
The external resistor divider is used to set the
output voltage (see the schematic on front page). The
feedback resistor R1 also sets the feedback loop
bandwidth with the internal compensation capacitor
(see Figure 1). Choose R1 to be around
300kΩ for
optimal transient response. R2 is then given by:
R
2
=
R
1
V
OUT
/ 0.805
−
1
R1(K
Ω)
300(1%)
300(1%)
300(1%)
300(1%)
300(1%)
300(1%)
R2(KΩ)
96(1%)
57.1(1%)
21.4(1%)
16.9(1%)
10.2(1%)
7.6(1%)
Table 1 –Resistor Selection for Common
Vout(V)
3.3
5
12
15
24
32
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Selecting the Inductor
33µH to 100µH inductor with a DC current rating
of at least 30% percent higher than the maximum load
current is recommended for most applications. For
highest efficiency, the inductor DC resistance should be
less than 50mΩ.
For most designs, the inductance value
can be derived from the following equation.
Table 2 –Sense Resistor Selection
Max. output current
（A）
Rsense（mΩ）
0.8
1.0
2.0
50
40
30
L
=
V
OUT
×
(
V
IN
−
V
OUT
)
V
IN
× ∆
I
L
× ƒ
sw
Loop compensation
A 12pf-82pf ceramic capacitor connected between
FB and OUT can optimize the loop stability for both
bandwidth and phase margin, recommended a 22-47pf
ceramic capacitor in most case.
Where ΔIL is the inductor ripple current. Choose
inductor current ripple to be approximately 30%-40%
of the maximum load current,. The maximum inductor
peak current is:
I
L
(
MAX
)
=
Iout
(
MAX
)
+
∆
I
L
2
PCB Layout
1) Under the large output current and high input
voltage case, the schottky diode and the converter
is the main heat source, don’t put them too close,
the PCB layout should keep enough area for heat
dissipation. Recommended ratio is 6:4 for schottky
diode and the convertor，for the cost issues, the
normal selection of PCB is 1oz thickness, the thick
solder tin is benefit on heat dissipation.
2) ILIM is internal connected the power MOS, the
heat dissipation should be considered for this pin.
3) The large current path (ILIM
、SW)
should be put
closer the converter as possible, use short, straight,
wide copper foil connect.
4) Input capacitor should be put as close as possible
to Vin and GND.
5) The loop of input capacitor, internal power MOS
and schottky diode is the highest di/dt radiation
region，reduce this region as possible. a 0.1uF
ceramic capacitor can be used to form a small loop
with internal power MOS and schottky diode,
which can reduce the switch ringing caused by
PCB parasitic inductor.
6) The outside feedback resistor should be placed
nearby the FB pin and keep away from SW node.
7) A 220pf ceramic capacitor between VIN and SW
pin can be used to reduce the switch negative
overshoot and improve EMI performance when
needed.
Under light load conditions below 100mA, larger
inductance is recommended for improved efficiency.
Selecting the Input Capacitor
The input capacitor reduces the surge current drawn
from the input and also the switching noise from the
device. The input capacitor impedance at the switching
frequency should be less than the input source
impedance to prevent high frequency switching current
from pass to the input. For most applications, a 47uF to
100uF electrolytic capacitor is sufficient.
Selecting the Output Capacitor
The output capacitor keeps output voltage small
and ensures regulation loop stability. The output
capacitor impedance should be low at the switching
frequency. a 220uF electrolytic capacitor is
recommended.
ILIM sense resistor
Power current flow into the chip via the external
accuracy sense resistor which defined the maximum
peak current. In guarantee under the normal start up
with full load, the sense resistor is recommended use
the larger value to ensure less surge current and output
output short power dissipation. The sense resistor value
should be reduced when used it at low temperature
situation to ensure enough startup energy.
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TYPICAL APPLICATION
3
C1A
10 µF
0
100V
VIN
ILIM
BS
8
R3
10Ω
C3
100nF
C1B
2
R4
0.1µF
30mΩ
100V
6
TX4139
EN
SW
1
D1
SS310
L1
33µΗ
5V/2A
ILIM(9)
C4
47pF
R1
300K
1%
R2
57.1K
1%
C2
22 µF
0
16V
POK
7
GND
4
FB 5
5V/2A BOM LIST:
Ref
C1A
C1B
C2
C3
C4
D1
L1
R1
R2
R3
R4
U1
Value
100uF
0.1uF
220uF
100nF
47pF
3A
33uH
300KΩ
57.1KΩ
10Ω
30mΩ
Description
Electrolytic,100V
Ceramic capacitor,100V
Electrolytic,16V
Ceramic capacitor, 100V, X7R
Ceramic, capacitor 25V, X7R
Schottky Diode, SMD, 100V, 3A
Inductor CDRH104, 2.4A
Film Res., 1%
Film Res., 1%
Film Res., 1%
Film Res., 1%
DC-DC convertor
Package
ELC SMD
0603
ELC SMD
0603
0603
SMB
CDRH104
0603
0603
0603
1206
ESOP8
TX4139
Panasonic
Panasonic
Panasonic
Manufacturer
jiang hai
muRata
jiang hai
muRata
muRata
Qty
1
1
1
1
1
1
1
1
1
1
1
1
ERJ-3EKF3003V
ERJ-3EKF5712V
ERJ-3EKF0011V
Manufacturer P/N
VTD-100V100
GRM188R71C104K
VTD-100V220
GRM188R71C104K
GRM32DR71E470K
SS310
Note： recommended to use a low Vf schottky diode for efficiency promotion.
95%
90%
85%
EFFICIENCY
80%
75%
70%
65%
60%
55%
50%
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
VOUT=5V
VIN=12V
VIN=24V
VIN=36V
VIN=48V
VIN=60V
VIN=72V
1.6
1.8
2.0
IOUT(A)
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测试/测量
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