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)
1/12
Axelite Confidential Materials, do not copy or distribute without written consent.
Rev1.4 Mar.26, 2015
AX3701
BLOCK DIAGRAM
PIN ASSIGNMENT
The packages of AX3701 are SOT-23-5L and TDFN-6L, the pin assignment is given by:
FB
5
VIN
4
SW
5
(Top View)
SOT-23-5L
FB
4
(Top View)
SOT-23-5L
1
2
3
1
2
3
EN
EN GND SW
SOT-23-5L (A Type)
FB GND SW
6
5
4
VIN GND
Name
EN
GND
SOT-23-5L (B Type)
Description
Enable pin
H：normal operation
L：Shutdown
Ground Pin
Switch output pin. Connect external
inductor here. Minimize trace area at
this pin to reduce EMI.
Power Supply Input Pin
Output Feedback pin
GND
1
2
3
SW
VIN
FB
NC EN VIN
TDFN-6L (2*2)
2/12
Axelite Confidential Materials, do not copy or distribute without written consent.
Rev1.4 Mar.26, 2015
AX3701
ORDER/MARKING INFORMATION
Order Information
AX3701 X X X X
Pin Type
A: A Type
B: B Type
(For SOT-23-5L Only)
Package Type
Packing
Blank : Bag
B: SOT-23-5L
Z6: TDFN-6L (2X2) A : Taping
Top Marking (TDFN-6L)
Top Marking
(SOT-23-5L A/B Type)
XX Y W X
ID code: internal
Za
YWX
Part Number
ID Code: Internal
Week: 01~26(A~Z)
27~52(a~z)
Year : A = 2010
1 = 2011
:
:
9 = 2019
WW: 01~26(A~Z)
27~52(a~z)
Year: A=2010
Za: AX3701 (A Type)
1=2011
Zf: AX3701 (B Type)
2=2012
:
:
9=2019
ABSOLUTE MAXIMUM RATINGS
(at T
A
= 25°C)
Characteristics
Symbol
Rating
Unit
VIN Pin Voltage
V
IN
V
SS
- 0.3 to V
SS
+ 8
V
2ms Pulse width VIN tolerance
V
PLUSE
V
SS
- 0.3 to V
SS
+ 10
V
Feedback Pin Voltage
V
FB
V
SS
- 0.3 to V
CC
+ 0.3 V
EN Pin Voltage
V
EN
V
SS
- 0.3 to V
CC
+ 0.3 V
Switch Pin Voltage
V
SW
V
SS
- 0.3 to V
CC
+ 0.3 V
Peak SW Sink and Source Current
I
PSW
1.5
A
Power Dissipation
PD
( T
J
-T
A
) / θ
JA
mW
Storage Temperature Range
T
ST
-40 to +150
°C
Operating Temperature Range
T
OP
-40 to +85
°C
Junction Temperature
T
J
+125
°C
ESD HBM
HBM
±2
KV
ESD MM
MM
±200
V
TDFN-6L(2*2)
25
Thermal Resistance from Junction
θ
JC
°C/W
to case
SOT-23-5L
130
TDFN-6L(2*2)
120
Thermal Resistance from Junction
θ
JA
°C/W
to ambient
SOT-23-5L
250
Note: θ
JA
is measured with the PCB copper area of approximately 1 in
2
(Multi-layer). That need connect to GND pin
of the AX3701.
3/12
Axelite Confidential Materials, do not copy or distribute without written consent.
Rev1.4 Mar.26, 2015
AX3701
ELECTRICAL CHARACTERISTICS
(V
IN
= V
EN
=3.6V, T
A
=25°C, unless otherwise specified) (Note)
Characteristics
Symbol
Conditions
Input Voltage Range (Note 2)
Under Voltage Lock Out
threshold
Feedback Voltage
Feedback Bias Current
Quiescent Current
Shutdown Supply Current
Switching Current Limit
Line Regulation
Load Regulation
Oscillation Frequency
R
DS(ON)
of P-CH MOSFET
R
DS(ON)
of N-CH MOSFET
Efficiency
EN pin logic input threshold
voltage
EN Pin Input Current
Soft-Start Interval
V
IN
V
UVLO
V
FB
I
FB
I
CC
I
SD
I
LIMIT
△V
OUT
/V
OUT
F
OSC
R
DSON
R
DSON
EFFI
V
ENL
V
ENH
I
EN
T
SS
V
IN
Rising
Hysteresis
V
FB=
0.6V
V
FB
=0.65V
V
FB
=1V
V
EN
=0V
VIN=5V
V
IN
= 2.5V~5.5V
SW pin
I
OUT
=1.0A
I
OUT
=1.0A
V
IN
=5V, V
OUT
=3.3V,
I
OUT
=0.5A
Min
2.5
1.8
100
-30
-
-
-
-
1.2
-
-
92
-
1.2
-
-
Typ
-
2.1
250
-
200
0.1
1.8
0.04
0.5
1.4
0.26
0.26
-
-
-
±0.1
1.2
Max Units
7.5
2.3
400
+30
400
1
0.4
0.6
1.6
0.33
0.33
-
0.6
-
±1
-
V
V
mV
nA
uA
uA
A
%/V
%
MHz
Ω
Ω
%
V
uA
ms
0.5880 0.6000 0.6120 V
△V
OUT
/V
OUT
I
OUT
= 0.01 to 1.2A
Note 1: 100% production test at +25°C. Specifications over the temperature range are guaranteed by design and
characterization.
Note 2: V
IN
(Min.) > V
OUT
(Max.) + I
O
(Max.)
˙
(P-CH MOSFET R
DS(ON)
+LDCR)
APPLICATION CIRCUIT
VIN
L1
V
IN
C1
4.7uF
EN
GND
FB
R1
60kΩ
SW
2.2uH
C3
330pF
(Option)
C2
10uF
V
OUT
=1.8V
R2
30kΩ
V
OUT
=0.6*(1+R1/R2)
4/12
Axelite Confidential Materials, do not copy or distribute without written consent.
Rev1.4 Mar.26, 2015
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
OUT
= 1.8V with input voltage range from 2.5V to 7.5V.
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
COMP,
limits the peak
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
ZERO
, or the beginning of the next clock cycle. The OVDET
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
ZERO,
and the switch voltage will ring. This is
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.
5/12
Axelite Confidential Materials, do not copy or distribute without written consent.
Rev1.4 Mar.26, 2015
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