AME5296 2A, 18V, 500KHz Synchronous Step Down DC

AME
AME5296
n General Description
The AME5296 is a high frequency synchronous
stepdown DC-DC cnverter with built internal power
MOSFETs. That provides wide 4.5V to 18V input voltage
range and 2A continuous load current capability. The
AME5296 has synchronous mode operation for higher
efficiency over output current load range.
2A, 18V, 500KHz Synchronous
Step Down DC/DC Converter
n Typical Application
VIN 4.5-18V
C1
22uF
25V
C3
1uF
BST
R4
10Ω
C4 0.1uF
VCC
SW
R1
40.2K
SS
C4
22nF
EN
EN
GND
FB
3.3V 2A
VOUT
L1
4.7uH
AME5296
The AME5296 is current mode control scheme which
provides fast transient response. Internal compensation
function.
n Features
IN
C2
47uF
R3
33K
R2
12.7K
l Wide 4.5V to 18V Operating Input Range
l 100mΩ/40mΩ Low RDS(ON) internal Power
MOSFETs
l Proprietary Switching Loss Reduction Techn
-ique
l High Efficiency Synchronous Mode Operation
l Fixed 500KHz Switching Frequency
l External Programmable Soft Start
l OCP and Hiccup
l Thermal Shutdown
l Output Adjustable from 0.8V
l RoHS Compliant and Halogen Free
n Application
l
l
l
l
Rev. A.05
Notebook Systems and I/O Power
Digital Set Top Boxes
LCD Display, TV
Networking, XDSL Modem
1
AME
2A, 18V, 500KHz Synchronous
Step-Down DC/DC Converter
AME5296
n Functional Block Diagram
IN
VCC
VCC
Regulator
M
RSEN
Current Sense
Amplifer
VCC
SS
BST
Oscillator
HS
Driver
1pF
EN
Reference
50pF 400k
SW
Current Limit
Comparator
Comparator
On Time Control
Logic Control
VCC
LS
Driver
1MEG
FB
Error Amplifer
2
GND
Rev. A.05
AME
2A, 18V, 500KHz Synchronous
Step Down DC/DC Converter
AME5296
n Pin Configuration
TSOT-23-8
Top View
8
7
6
AME5296-AEAxxx
1. SS
2. IN
3. SW
4. GND
5. BST
6. EN
7. VCC
8. FB
5
AME5296
1
2
3
4
* Die Attach:
Conductive Epoxy
n Pin Description
Pin No.
Pin Name
1
SS
Soft-Start Control Input. SS controls the soft-start period. Connect a
capacitor from SS to GND to set the soft-start period.
2
IN
Supply Voltage. The AME5296 operates from a +4.5V to +18V input rail. C1
is needed to decouple the input rail. Use wide PCB trace to make the
connection.
3
SW
Switch Node. Connect this pin to an external L-C filter.
4
GND
System Ground. This pin is the reference ground of the regulated output
voltage. For this reason care must be taken in PCB layout. Suggested to be
connected to GND with copper and vias.
5
BST
Bootstrap for High Side Gate Driver. Connect a 0.1µF or greater ceramic
capacitor from BST to SW pins.
6
EN
7
VCC
8
FB
Rev. A.05
Pin Description
EN=1 to enable the AME5296. EN=0 to turn-off the AME5296.
Bias Supply. Decouple with a 0.1µF-to-1µF cap.
Feedback Input. It is used to regulate the output of the converter to a set
value via an external resistive voltage divider.
3
AME
2A, 18V, 500KHz Synchronous
Step-Down DC/DC Converter
AME5296
n Ordering Information
AME5296 - x x x xxx x
Special Feature
Output Voltage
Number of Pins
Package Type
Pin Configuration
Pin Configuration
A
(TSOT-23-8)
4
1. SS
2. IN
3. SW
4. GND
5. BST
6. EN
7. VCC
8. FB
Package
Type
Number of
Pins
Output Voltage
Special Feature
E: SOT-2X
A: 8
ADJ: Adjustable
L: TSOT-23-8 (Low Profile)
Rev. A.05
AME
2A, 18V, 500KHz Synchronous
Step Down DC/DC Converter
AME5296
n Absolute Maximum Ratings
Parameter
Maximum
Unit
VIN
-0.3 to 19
V
VSW
-0.3V (-5V for 10ns) to 19V (20V for 5ns)
V
VBST
VSW+6V
V
-0.3 to 6.5
V
All Other Pins
Junction Temperature
Lead Temperature
Storage Temperature
150
o
C
260
o
C
-65 to +150
o
C
n Recommended Operating Conditions
Parameter
Symbol
Rating
VIN
4.5V to 18V
VOUT
0.8V to VIN-3V
Junction Temperature Range
TJ
-40 to +125
Ambient Temperature Range
TA
-40 to +85
Input Voltage
Output Voltage
Unit
V
o
C
n Thermal Information
Parameter
Package
Die Attach
Thermal Resistance*
(Junction to Case)
Thermal Resistance
(Junction to Ambient)
Symbol
Maximum
θJ C
55
Unit
o
TSOT-23-8
Conductive Epoxy
Internal Power Dissipation
Lead Temperature (Soldering 10sec)**
θJA
100
PD
1250
260
C/W
mW
o
C
* Measure θJC on backside center of molding compound if IC has no tab.
** MIL-STD-202G 210F
Rev. A.05
5
AME
2A, 18V, 500KHz Synchronous
Step-Down DC/DC Converter
AME5296
n Electrical Specifications
VIN=12V, unless otherwise noted. Typical values are at TA=25oC.
Parameter
Symbol
Test Condition
Supply Shutdown Current
IIN
VEN=0V
0.1
µA
Supply Current
IQ
VEN=2V, VFB=1V, VSS=3V
0.7
mA
High Side Switch On-Resistance
RDS(ON)1
VBST-SW=5V
100
mΩ
Low Side Switch On-Resistance
RDS(ON)2
VCC=5V
40
mΩ
Load Side Switch Leakage
Current
SW LKG
VEN=0V, VSW=12V
0.15
µA
Switch Current Limit
Typ
Max
2.8
Units
A
Oscillator Frequency
fOSC1
VFB=0.75V
500
KHz
Fold-back Frequency
fFB
VFB<400mV
0.25
fSW
Maximum Duty Cycle
DMAX
VFB=700mV
90
95
%
-2%
800
2%
mV
10
50
nA
o
o
Feedback Voltage
VFB
-40 C<TA<85 C
Feedback Current
IFB
VFB=800mV
EN Rising Threshold
VEN_RISING
1.2
1.4
1.6
V
EN Falling Threshold
VEN_FALLING
1.1
1.25
1.4
V
EN Input Current
EN Turn Off Delay
IEN
VUVLO
Input Under Voltage Lockout
Hysteresis
Thermal Hysteresis
2
µA
VEN=0V
0
µA
8
µs
3.6
V
∆VUVLO
600
mV
VCC
5
V
5
%
VCC Load Regulation
Thermal Shutdown
VEN=2V
ENTD-OFF
Input Under Voltage Lockout
Threshold
VCC Regulator
6
Min
ICC=5mA
TSD
150
o
C
20
o
C
Rev. A.05
AME
AME5296
n Detailed Descriptiion
Internal VCC Regulator
The internal VCC regulator is adjusted 5.0V to provide
power to the internal circuits from input voltage VIN. In
order to maintain the VCC voltage stably, a 0.1µ F-to-1µF
ceramic capacitor is recommended.
2A, 18V, 500KHz Synchronous
Step Down DC/DC Converter
Thermal Shutdown
The AME5296 protects itself from overheating with an
internal thermal shutdown circuit. If the junction temperature exceeds the thermal shutdown threshold, the voltage
reference is grounded and the shutdown mode is activated.
The AME5296 is restarted under control of the soft start
automatically when the junction temperature drops 20oC
below the thermal shutdown threshold.
Enable and Soft Start
The EN pin provides electrical on/off control of the regulator. When the EN pin voltage exceeds the lockout
threshold voltage, the regulator starts to operate and the
soft start begins to charge the external capacitor. If the
EN pin voltage is pulled below the lockout threshold voltage, the regulator stops switching and the soft start resets. Connecting the EN pin to ground or to any voltage
less than 1.2V will disable the regulator and activate the
shutdown mode. To limit the start-up inrush current, a
soft-start circuit is used to ramp up the reference voltage
from 0V to its final value linearly. The soft start time can
be calculated as follows:
t SS =
0.8 × CSS
ISS
Under Voltage Lockout (UVLO)
The AME5296 incorporates an under voltage lockout circuit to keep the device disabled when the input voltage VIN
is below the UVLO start threshold voltage. During powering up, the internal circuits are held inactive and the soft
start is grounded until the input voltage VIN exceeds the
UVLO start threshold voltage. Once the UVLO start threshold voltage is reached, the soft start is activated and the
device begins to operate. The device operates until the
input voltage VIN falls below the UVLO stop threshold voltage. The typical hysteresis in the UVLO comparator is
650mV.
Rev. A.05
Over-Current Protection and Hiccup Mode
The over-current limiting is implemented by cycle-bycycle monitoring the current through the high side MOSFET.
If the peak current exceeds the over-current limit threshold, the high side MOSFET is turned off. When the feedback voltage VFB drops below 0.4V, the oscillator frequency
is reduced to about 1/4 of the normal frequency to ensure
that the inductor current has more time to decay, thereby
preventing runaway. Meanwhile, the AME5296 enters hiccup mode, the average short circuit current is greatly reduced to alleviate the thermal issue and to protect the
regulator.
Enternal Bootstrap Circuit
The external bootstrap circuit contains a capacitor and a
resistor. A bootstrap capacitor provides power for the high
side MOSFET driver. In order to supply the AC current and
maintain the BST-SW voltage stably at the switching condition of the high side MOSFET, a 1µF low ESR ceramic
capacitor is recommended. The bootstrap resistor which
suggests placing 10Ω is utilized to reduce switching spike
voltage and noise.
7
AME
AME5296
n Application Information
Inductor Selection
For most applications, the inductance range is chosen
based on the desired ripple current. A larger inductance
reduces ripple current; meanwhile, the output ripple voltage decreases. Determine inductance is to allow the peakto-peak ripple current to be approximately 30% of the
maximum load current. The inductance value can be calculated by:
L=
VOUT
V
× 1 − OUT
f × IL
VIN
Where f is the oscillator frequency, VIN is the input voltage, VOUT is the output voltage, and ∆IL is the peak-to-peak
inductor ripple current. Choose an inductor that will not
saturate under the maximum inductor peak current, calculated by:
I LPEAK = I LOAD +
VOUT
V
× 1 − OUT
2 × f × IL
VIN
Where ILOAD is the load current. The choice of which
style inductor to use mainly depends on the price vs. size
requirements and any EMI constraints.
The input current to the buck converter is discontinuous; therefore an input capacitor is required to supply the
AC current while maintaining the DC input voltage. In order to prevent large voltage drop, a low ESR capacitors is
recommended for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic
capacitors will also be suggested. Choose X5R or X7R
dielectrics when using ceramic capacitors. Since the input capacitor absorbs the input switching current, it requires an adequate ripple current rating. The RMS current
in the input capacitor can be estimated by:
8
At VIN = 2VOUT, where ICIN = ILOAD/2 is the worst-case
condition occurs. For simplification, use an input capacitor with a RMS current rating greater than half of the maximum load current. When using ceramic capacitors, make
sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input.
When using electrolytic or tantalum capacitors, a high
quality, small ceramic capacitor, i.e. 1µF, should be placed
as close to the IC as possible. The input voltage ripple for
low ESR capacitors can be estimated by:
VIN =
I LOAD VOUT
V
×
× 1 − OUT
C IN × f VIN
VIN
Where CIN is the input capacitance value.
Output Capacitor
The output capacitor (COUT) is required to maintain the
DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low.
The output voltage ripple can be estimated by:
VOUT =
Input Capacitor
I CIN = I LOAD ×
2A, 18V, 500KHz Synchronous
Step-Down DC/DC Converter
V
VOUT
× 1 − OUT
VIN
VIN
VOUT
V
1
× 1 − OUT × R ESR +
f ×L
VIN
8 × f × COUT
Where RESR is the equivalent series resistance (ESR)
value of the output capacitor and COUT is the output capacitance value.
When using ceramic capacitors, the impedance at the
switching frequency is dominated by the capacitance which
is the main cause for the output voltage ripple. For simplification, the output voltage ripple can be estimated by:
VOUT =
VOUT
V
× 1 − OUT
8 × f × L × C OUT
VIN
2
Rev. A.05
AME
2A, 18V, 500KHz Synchronous
Step Down DC/DC Converter
AME5296
When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For
simplification, the output ripple can be approximated to:
VOUT =
V
VOUT
× 1 − OUT × R ESR
VIN
f ×L
Setting the Output Voltage
The output voltage is using a resistive voltage divider connected from the output voltage to feedback pin. It divides the
output voltage down to the feedback voltage by the ratio:
VFB = VOUT ×
R2
R1 + R 2
The output voltage is:
VOUT = 0.8 ×
R1 + R 2
R2
n Typical Application Circuits
VIN
4.5V~18V
Ren1
18K
IN
CIN2
NS
CIN1
22uF
BST
C3
1uF
C5
22nF
Rev. A.05
C4
0.1uF
AME5296
L1
4.7uH
VOUT
3.3V/2A
SW
EN
Ren2
10K
R4
10Ω
VCC
R1
40.2K
SS
R3
33K
FB
C6
15pF
COUT 1
22uF
COUT2
22uF
R5
0Ω
R2
12.7K
GND
VOUT(V)
R1(KΩ)
R2(KΩ)
R3(KΩ)
L(µH)
CIN(µF)
COUT(µF)
1.0
20.5
82.0
82
1.5
22
22x2
1.2
30.1
60.4
82
1.5
22
22x2
1.8
40.2
32.4
56
2.2
22
22x2
2.5
40.2
19.1
33
3.3
22
22x2
3.3
40.2
12.7
33
4.7
22
22x2
5.0
40.2
7.68
33
6.8
22
22x2
9
AME
2A, 18V, 500KHz Synchronous
Step-Down DC/DC Converter
AME5296
n Characterization Curve
Output Voltage Ripple
Load Transient
VIN=12V, VOUT=3.3V, IOUT=0.5~2A
VOUT
(200mV/Div)
IL
(1A/Div)
C3
VOUT
(2V/Div)
C2
VSW
(5V/Div)
C3
IL
(2A/Div)
C4
VEN
(5V/Div)
V OUT
(2V/Div)
VSW
(10V/Div)
C3
C4
Time(2µs/Div)
Power On from Input Voltage
Power On from Input Voltage
V IN
(5V/Div)
VOUT
(2V/Div)
VSW
(5V/Div)
IL
(2A/Div)
VIN=12V, VOUT=3.3V
IOUT=2A
C1
C2
C3
C4
Time(5ms/Div)
Time(5ms/Div)
Power On from EN
Power on from EN
VEN
(5V/Div)
C1
C2
C2
VIN=12V, VOUT=3.3V, IOUT=2A
Time(200µF/Div)
VIN=12V, VOUT=3.3V
IOUT=0A
C1
C1
VOUT
(20mV/Div)
IL
(2A/Div)
C4
VIN
(5V/Div)
VIN(AC)
(100mV/Div)
VIN=12V, VOUT=3.3V
IOUT=0A
VOUT
(2V/Div)
C1
C2
VIN=12V, VOUT=3.3V
IOUT=2A
C3
VSW
(5V/Div)
IL
(2A/Div)
VSW
(5V/Div)
IL
(2A/Div)
C3
C4
Time(5ms/Div)
10
C4
Time(5ms/Div)
Rev. A.05
AME
2A, 18V, 500KHz Synchronous
Step Down DC/DC Converter
AME5296
Power Off from Input Voltage
VIN
(5V/Div)
V OUT
(2V/Div)
VIN=12V, VOUT=3.3V, IOUT=0A
Power Off from Input Voltage
V IN
(5V/Div)
VOUT
(2V/Div)
C1
C3
VEN
(5V/Div)
VOUT
(2V/Div)
VSW
(5V/Div)
IL
(2A/Div)
C4
C1
C1
C2
C2
VSW
(5V/Div)
IL
(2A/Div)
VIN=12V, VOUT=3.3V, IOUT=2A
VSW
(5V/Div)
C3
IL
(2A/Div)
C4
Time(50ms/Div)
Time(5ms/Div)
Power Off from EN
Power Off from EN
VIN=12V, VOUT=3.3V, IOUT=0A
VEN
(5V/Div)
VOUT
(2V/Div)
C2
C2
VSW
(5V/Div)
C3
C3
IL
(2A/Div)
C4
VOUT
(1V/Div)
C4
Time(2s/Div)
Time(5ms/Div)
Short Circuit Entry
Short Circuit Recovery
VIN=12V, VOUT=3.3V,
IOUT=0A
VIN=12V, VOUT=3.3V, IOUT=0A
VSS
(1V/Div)
VSW
(10V/Div)
IL
(5A/Div)
VOUT
(1V/Div)
C3
C2
C1
C4
Time(5ms/Div)
Rev. A.05
VIN=12V, VOUT=3.3V,
IOUT=2A
C1
C3
VSW
(10V/Div)
VSS
(1V/Div)
C1
IL
(5AD/iv)
C4
C2
Time(5ms/Div)
11
AME
2A, 18V, 500KHz Synchronous
Step-Down DC/DC Converter
AME5296
Efficiency
12V
18V
VOUT =5V, IOUT =0~2A
100
100
90
90
80
Efficiency (%)
Efficiency (%)
18V
Efficiency
70
60
50
40
30
20
10
0
12V
5V VOUT=3.3V, IOUT =0~2A
80
70
60
50
40
30
20
10
0.0
0.5
1.0
1.5
2.0
0
0.0
0.5
1.0
1.5
2. 0
Output Current (A)
Output Current (A)
Efficiency
5V
12V
18V VOUT =1.2V, IOUT =0~2A
100
Efficiency (%)
90
80
70
60
50
40
30
20
10
0
0.0
0. 5
1.0
1.5
2. 0
Output Current (A)
12
Rev. A.05
AME
2A, 18V, 500KHz Synchronous
Step Down DC/DC Converter
AME5296
n Tape and Reel Dimension
TSOT-23-8
P0
W
AME
AME
PIN 1
P
Carrier Tape, Number of Components Per Reel and Reel Size
Package
Carrier Width (W)
Pitch (P)
Pitch (P0)
Part Per Full Reel
Reel Size
TSOT-23-8
8.0±0.1 mm
4.0±0.1 mm
4.0±0.1 mm
3000pcs
180±1 mm
n Package Dimension
TSOT-23-8
Top View
Side View
D
L
b
E
E1
0.25
PIN 1
e
C
e1
A
A1
A2
Front View
Rev. A.05
13
www.ame.com.tw
E-Mail: sales@ame.com.tw
Life Support Policy:
These products of AME, Inc. are not authorized for use as critical components in life-support
devices or systems, without the express written approval of the president
of AME, Inc.
AME, Inc. reserves the right to make changes in the circuitry and specifications of its devices and
advises its customers to obtain the latest version of relevant information.
 AME, Inc. , October 2014
Document: A018A-DS5296-A.05
Corporate Headquarter
AME, Inc.
8F, 12, WenHu St., Nei-Hu
Taipei 114, Taiwan .
Tel: 886 2 2627-8687
Fax: 886 2 2659-2989