Page 1
AX3701
1.4MHz, 1.2A, VFB=0.6V Synchronous Step-Down
Converter
GENERAL DESCRIPTION
AX3701 is a high efficiency monolithic synchronous buck regulator using a constant
frequency, current mode architecture. The device is available in an adjustable version.
Supply current with no load is about 200uA and drops to <1uA in shutdown. The 2.5V to
7.5V input voltage range makes AX3701 ideally suited for single Li-Ion, two to four AA
battery-powered applications. 100% duty cycle provides low dropout operation, extending
battery life in portable systems. Pulse skipping mode operation provides very low output
ripple voltage for noise sensitive applications. Switching frequency is internally set at
1.4MHz, allowing the use of small surface mount inductors and capacitors. The internal
synchronous switch increases efficiency and decreases need of an external Schottky diode.
Low output voltages are easily supported with the 0.6V feedback reference voltage. AX3701
is available in small SOT-23-5L, TDFN-6L (2*2) packages.
FEATURES
- 2.5V to 7.5V Input Voltage Range
- Output Voltage from 0.6V to V
IN
- High Efficiency: Up to 92%
- 1.4MHz Constant Frequency Operation
- 1.2A Output Current
- Quiescent Current: 200uA (input < 4.2V)
- No Schottky Diode Required
- 100% Duty Cycle in Dropout
- 0.6V Reference Allows Low Output Voltages
- Current Mode Operation for Excellent Line and Load Transient Response
- Current limit, Enable function
- Short Circuit Protect (SCP)
- ≤ 1µA Shutdown Current
- SOT-23-5L, TDFN-6L (2*2)
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Rev1.4 Mar.26, 2015
Page 2
AX3701
(Top View)
EN GND SW
VINFB
1
2 3
4
SOT-23-5L
5
SOT-23-5L (A Type)
(Top View)
VIN GND EN
FBSW
1
2 3
4
SOT-23-5L
5
SOT-23-5L (B Type)
TDFN-6L (2*2)
VIN
FB
SW
1 2
3
456
EN
GND
NC
GND
Name
Description
EN
Enable pin
H：normal operation
L：Shutdown
GND
Ground Pin
SW
Switch output pin. Connect external
inductor here. Minimize trace area at
this pin to reduce EMI.
VIN
Power Supply Input Pin
FB
Output Feedback pin
BLOCK DIAGRAM
PIN ASSIGNMENT
The packages of AX3701 are SOT-23-5L and TDFN-6L, the pin assignment is given by:
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Rev1.4 Mar.26, 2015
Page 3
AX3701
Order Information
Package Type
AX3701
Packing
A : Taping
X X X
B: SOT-23-5L
X
Pin Type
A: A Type
B: B Type
(For SOT-23-5L Only)
Blank : Bag
Z6: TDFN-6L (2X2)
Top Marking (TDFN-6L)
Top Marking
(SOT-23-5L A/B Type)
Z a
Y W X
Year : A = 2010
1 = 2011
Part Number
Week: 01~26(A~Z)
27~52(a~z)
ID Code: Internal
:
:
9 = 2019
X
WW: 01~26(A~Z)
27~52(a~z)
Year: A=2010
1=2011
2=2012
ID code: internal
Za: AX3701 (A Type)
X
Y WX
:
:
9=2019
Zf: AX3701 (B Type)
Characteristics
Symbol
Rating
Unit
VIN Pin Voltage
VIN
VSS - 0.3 to VSS + 8
V
2ms Pulse width VIN tolerance
V
PLUSE
VSS - 0.3 to VSS + 10
V
Feedback Pin Voltage
VFB
VSS - 0.3 to VCC + 0.3
V
EN Pin Voltage
VEN
VSS - 0.3 to VCC + 0.3
V
Switch Pin Voltage
VSW
VSS - 0.3 to VCC + 0.3
V
Peak SW Sink and Source Current
I
PSW
1.5
A
Power Dissipation
PD
( TJ-TA ) / θJA
mW
Storage Temperature Range
TST
-40 to +150
°C
Operating Temperature Range
TOP
-40 to +85
°C
Junction Temperature
TJ
+125
°C
ESD HBM
HBM
±2
KV
ESD MM
MM
±200
V
Thermal Resistance from Junction
to case
TDFN-6L(2*2)
θJC
25
°C/W
SOT-23-5L
130
Thermal Resistance from Junction
to ambient
TDFN-6L(2*2)
θJA
120
°C/W
SOT-23-5L
250
ORDER/MARKING INFORMATION
ABSOLUTE MAXIMUM RATINGS (at T
Note: θJA is measured with the PCB copper area of approximately 1 in2(Multi-layer). That need connect to GND pin
of the AX3701.
Axelite Confidential Materials, do not copy or distribute without written consent.
= 25°C )
A
3/12
Rev1.4 Mar.26, 2015
Page 4
AX3701
Characteristics
Symbol
Conditions
Min
Typ
Max
Units
Input Voltage Range (Note 2)
VIN
2.5 - 7.5
V
Under Voltage Lock Out
threshold
V
UVLO
VIN Rising
1.8
2.1
2.3
V
Hysteresis
100
250
400
mV
Feedback Voltage
VFB
V
FB=
0.6V
0.5880
0.6000
0.6120
V
Feedback Bias Current
IFB
VFB=0.65V
-30 - +30
nA
Quiescent Current
ICC
VFB=1V
-
200
400
uA
Shutdown Supply Current
ISD
VEN =0V
-
0.1 1 uA
Switching Current Limit
I
LIMIT
VIN=5V
1.8 A
Line Regulation
△V
OUT/VOUT
VIN = 2.5V~5.5V
-
0.04
0.4
%/V
Load Regulation
△V
OUT/VOUT
I
OUT
= 0.01 to 1.2A
-
0.5
0.6
%
Oscillation Frequency
F
OSC
SW pin
1.2
1.4
1.6
MHz
R
DS(ON)
of P-CH MOSFET
R
DSON
I
OUT
=1.0A
-
0.26
0.33
Ω
R
DS(ON)
of N-CH MOSFET
R
DSON
I
OUT
=1.0A
-
0.26
0.33
Ω
Efficiency
EFFI
VIN=5V, V
OUT
=3.3V,
I
OUT
=0.5A
92 - -
%
EN pin logic input threshold
voltage
V
ENL
- - 0.6
V
V
ENH
1.2 - -
EN Pin Input Current
IEN
-
±0.1
±1
uA
Soft-Start Interval
TSS
- 1.2 - ms
V
IN
EN
GND
SW
FB
C1
4.7uF
R1
60kΩ
R2
30kΩ
C3
330pF
(Option)
C2
10uF
V
OUT
=1.8V
L1
2.2uH
VIN
ELECTRICAL CHARACTERISTICS
(VIN = VEN=3.6V, T
=25°C, unless otherwise specified) (Note)
A
Note 1: 100% production test at +25°C. Specifications over the temperature range are guaranteed by design and
characterization.
Note 2: VIN (Min.) > V
APPLICATION CIRCUIT
Axelite Confidential Materials, do not copy or distribute without written consent.
(Max.) + IO (Max.) ˙ (P-CH MOSFET R
OUT
V
=0.6*(1+R1/R2)
OUT
DS(ON)
+LDCR)
4/12
Rev1.4 Mar.26, 2015
Page 5
AX3701
FUNCTION DESCRIPTIONS
Operation
AX3701 is a monolithic switching mode step-down DC-DC converter. It utilizes internal
MOSFETs to achieve high efficiency and can generate very low output voltage by using
internal reference at 0.6V. It operates at a fixed switching frequency, and uses the slope
compensated current mode architecture. This step-down DC-DC Converter supplies 1.2A
output current at V
= 1.8V with input voltage range from 2.5V to 7.5V.
OUT
Current Mode PWM Control
Slope compensated current mode PWM control provides stable switching and
cycle-by-cycle current limit for excellent load and line responses and protection of the
internal main switch (P-Ch MOSFET) and synchronous rectifier (N-CH MOSFET). During
normal operation, the internal P-Ch MOSFET is turned on for a certain time to ramp the
inductor current at each rising edge of the internal oscillator, and switched off when the peak
inductor current is above the error voltage. The current comparator, I
limits the peak
COMP,
inductor current. When the main switch is off, the synchronous rectifier will be turned on
immediately and stay on until either the inductor current starts to reverse, as indicated by the
current reversal comparator, I
, or the beginning of the next clock cycle. The OVDET
ZERO
comparator controls output transient overshoots by turning the main switch off and keeping it
off until the fault is no longer present.
Idle Mode Operation
At very light loads, AX3701 automatically enters pulse skipping mode. In the pulse
skipping Mode, the inductor current may reach zero or reverse on each pulse. The control
loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is
turned off by the current reversal comparator, I
and the switch voltage will ring. This is
ZERO,
discontinuous mode operation, and is normal behavior for the switching regulator.
Maximum Load Current
AX3701 will operate with input supply voltage as low as 2.5V, however, the maximum
load current decreases at lower input due to large IR drop on the main switch and
synchronous rectifier. The slope compensation signal reduces the peak inductor current as a
function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than
50%. Conversely the current limit increases as the duty cycle decreases.
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Rev1.4 Mar.26, 2015
Page 6
AX3701
)
2R
1R
+1(×V6.0=V
OUT
V
OUT
R2
R1
1.2V
30K
30K
1.5V
30K
45K
1.8V
30K
60K
2.5V
30K
95K
3.3V
30K
135K
f
I
V
VVV
L
OSC
L
IN
OUTINOUT
V
OUT
1.2V
1.5V
1.8V
2.5V
3.3V
Inductor
2.2uH
2.2uH
2.2uH
2.2uH
2.2uH
APPLICATION INFORMATION
Setting the Output Voltage
Application circuit item shows the basic application circuit with AX3701 adjustable
output version. The external resistor sets the output voltage according to the following
equation:
Table 1 Resistor select for output voltage setting
We guarantee that the duty cycle range of 20% to 80% is able to work well.
Inductor Selection
For most designs, the AX3701 operates with inductors of 1µ H to 4.7µH. Low
inductance values are physically smaller but require faster switching, which results in some
efficiency loss. The inductor value can be derived from the following equation:
Where is inductor ripple current. Large value inductors lower ripple current and small
value inductors result in high ripple currents. Choose inductor ripple current approximately
35% of the maximum load current.
Table 2 Inductor select for output voltage setting (VCC=3.3V)
Note: Part type MH or M (www.we-online.com)
For output voltages above 2.0V, when light-load efficiency is important, the minimum
recommended inductor is 2.2µH. For optimum voltage-positioning load transients, choose
an inductor with DC series resistance in the 50mΩ to 150mΩ range. For higher efficiency at
heavy loads (above 200mA), or minimal load regulation (but some transient overshoot), the
resistance should be kept below 100mΩ. The DC current rating of the inductor should be at
least equal to the maximum load current plus half the ripple current to prevent core
saturation.
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Page 7
AX3701
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching
noise from the device. The input capacitor impedance at the switching frequency shall be
less than input source impedance to prevent high frequency switching current passing to the
input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic
capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR
and small temperature coefficients. A 4.7µF ceramic capacitor for most applications is
sufficient.
Output Capacitor Selection
The output capacitor is required to keep the output voltage ripple small and to ensure
regulation loop stability. The output capacitor must have low impedance at the switching
frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their
low ESR and high ripple current.
Compensation Capacitor Selection
The compensation capacitors for increasing phase margin provide additional stability.
It is required and more than 100pF, Refer to Demo Board Schematic, The optimum values
for C3 (option) is 330pF.
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Rev1.4 Mar.26, 2015
Page 8
AX3701
AX3701
12345
VIN
FB
EN
GND
SW
C1R2R1
C2
C3
L1
Net VIN
Net VIN
VIN
VOUT
GND
GND
AX3701
123
VINFBEN
GND
SW
C1
R2
R1C2C3
L1
VIN
VOUT
GND
GND
654
NC
PCB Layout Recommendations
When laying out the printed circuit board, the following checking should be used to
ensure proper operation of the AX3701. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be
kept short, direct and wide.
2. Does the (+) plates of CIN connect to VIN as closely as possible. This capacitor provides
the AC current to the internal power MOSFETs.
3. Keep the switching node SW away from the sensitive V
4. Keep the (-) plates of CIN and C
as close as possible.
OUT
OUT
node.
8/12
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Rev1.4 Mar.26, 2015
Page 9
AX3701
5V~10V VIN Overshoot Test,
No Load,1.8V
OUT
100mA~1A Load Transient Test,
5VIN to 1.8V
OUT
, C3=330PF
No Load Start Up and Shutdown,
5VIN to 1.8V
OUT
1A Load Start Up and Shutdown,
5VIN to 1.8V
OUT
Output Short Circuit Test,
5VIN to 1.8V
OUT
150°C Thermal Shutdown,
5VIN to 1.8V
OUT
, 1A Load
TYPICAL CHARACTERISTICS
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9/12
Rev1.4 Mar.26, 2015
Page 10
AX3701
1A Load Switching Waveform,
5VIN to 1.8V
OUT
No Load Switching Waveform,
5VIN to 1.8V
OUT
I
OUT
vs Efficiency, VIN=5V
TYPICAL CHARACTERISTICS (CONTINUOUS)
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Rev1.4 Mar.26, 2015
Page 11
AX3701
E
D
A
A 1
A3
D2
e
E 2
(Top View)
(Bottom View)
b
Pin 1
L
SEATING PLANE
(SIDE View)
Symbol
Dimensions in Millimeters
Dimensions in Inches
Min.
Nom.
Max.
Min.
Nom.
Max. A 0.7
0.75
0.8
0.028
0.03
0.031
A1 0 0.02
0.05
0
0.001
0.002
A3
0.203 REF.
0.008 REF.
b
0.2
0.28
0.35
0.009
0.011
0.013
D
1.95 2 2.05
0.077
0.079
0.081
D2
1.0
1.3
1.45
0.039
0.051
0.057
E
1.95 2 2.05
0.077
0.079
0.081
E2
0.5
0.65
0.85
0.02
0.026
0.033
e
0.65 BSC.
0.026 BSC.
L
0.2
0.3
0.4
0.008
0.012
0.016
PACKAGE OUTLINES
(1) TDFN-6L (2*2 0.75mm)
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Rev1.4 Mar.26, 2015
Page 12
AX3701
L
e1
E1
E
D
A2
A1
b(5x)
A
DETAL A
L1
1(4x)
2(4x)
e
GAUGE PLANE
C
DETAL A
θ
θ
θ
Symbol
Dimensions in Millimeters
Dimensions in Inches
Min.
Nom.
Max.
Min.
Nom.
Max. A - - 1.3 - -
0.051
A1
0
0.08
0.15
0
0.003
0.006
A2
0.9
1.1
1.3
0.035
0.043
0.051 b 0.3
0.4
0.5
0.012
0.016
0.02 C 0.08
0.15
0.22
0.003
0.006
0.009 D 2.7
2.9
3.1
0.106
0.114
0.122
E1
1.4
1.6
1.8
0.055
0.063
0.071 E 2.6
2.8
3
0.102
0.11
0.118
L
0.3
0.45
0.6
0.012
0.018
0.024
L1
0.5
0.6
0.7
0.02
0.024
0.028
e1
1.9 BSC
0.075 BSC
e
0.95 BSC
0.037 BSC
θ
0o
4o
8o
0o
4o
8o
θ1
5o
10o
15o
5o
10o
15o
θ2
5o
10o
15o
5o
10o
15o
JEDEC outline: NA
(2) SOT-23-5L
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12/12
Rev1.4 Mar.26, 2015
Page 13
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