AME AME5235 40v 3.5a buck converter Datasheet

AME
40V 3.5A Buck Converter
AME5235
n General Description
n Typical Application
The AME5235 is a specific 40V HV buck converter
supports an output voltage range of 0.8V to 12V at 200KHz
switching frequency.
Protection features include under voltage protection,
over voltage protection, current limit, thermal shutdown,
and short circuit protection. The device is available in
SOP-8/PP package with exposed pad for low thermal
R4 C3
10Ω 22nF
VIN=
8V~40V
IN
l
l
l
l
l
l
40V Maximum Rating for Input Power
200KHz Switching Frequency
Internal Soft Start
UVP, Input/Output OVP, OTP, SCP
Available in SOP-8/PP Package
RoHS Compliant and Halogen Free
SW
C1
47uF
AME5235
resistance.
n Features
L1
47uH
BS
COMP
C4
3.3nF
C5
Optional
R3
8.2K
R1
D1
SK 110K
34
FB
VBUS
C2
470 uF
R2
20K
GND
GND
n Functional Block Diagram
IN
n Application
Oscillator
l Car Charger
l Wall Adapter
Vref &
S/D
Control
EMI
Control
BS
PWM
Controller
SW
0.8V
FB
COMP
Rev. A.02
GND
1
AME
40V 3.5A Buck Converter
AME5235
n Pin Configuration
SOP-8/PP
Top View
8
7
6
AME5235-AZAADJ
1. IN
2. COMP
3. NC
4. NC
5. FB
6. GND
7. SW
8. BS
5
GND
1
2
3
4
* Die Attach:
Conductive Epoxy
n Pin Description
2
Pin No.
Pin Name
Pin Description
1
IN
2
COMP
3, 4
NC
No connection.
5
FB
Feedback Input.
6
GND
Ground.
7
SW
Power Switching Output
8
BS
High Side. Gate Drive Boost Input.
9
Exposed Pad
Input power.
Compensation Node.
Ground.
Rev. A.02
AME
40V 3.5A Buck Converter
AME5235
n Ordering Information
AME5235 - x x x xxx
Output Voltage
Number of Pins
Package Type
Pin Configuration
Pin Configuration
A
(SOP-8/PP)
Rev. A.02
1. IN
2. COMP
3. NC
4. NC
5. FB
6. GND
7. SW
8. BS
Package
Type
Z: SOP/PP
Number of Pins
A: 8
Output Voltage
ADJ: Adjustable
3
AME
40V 3.5A Buck Converter
AME5235
n Absolute Maximum Ratings
Parameter
Maximum
Unit
Input Voltage
-0.3V to 40
V
Switch Voltage
-1 to VIN +1
V
VSW - 0.3 to VSW + 7
V
-0.3V to 7
V
Electrostatic Discharge (HBM)
2000
V
Junction Temperature
150
o
-65 to +150
o
Boost Switch Voltage
All Other Pins
Storage Temperature
ESD Classification
C
C
HBM
2
kV
MM
150
V
n Recommended Operating Conditions
Parameter
Symbol
Rating
VIN
8 to 40
VOUT
0.8 to 12
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)
Maximum
θJ C
19
Unit
o
SOP-8/PP
Conductive Epoxy
Power Dissipation
Lead Temperature ( soldering 10 sec)**
4
Symbol
* Measure θJC on backside center of molding compound if IC has no tab.
** MIL-STD-202G 210F
C/W
θJA
84
PD
1450
260
mW
o
C
Rev. A.02
AME
40V 3.5A Buck Converter
AME5235
n Electrical Specifications
Typical values VIN=12V with typical TA=25oC, unless otherwise specified.
Parameter
Input Voltage Operating Range
VIN UVLO Rising Threshold
Voltage
VIN UVLO Hysteresis
Symbol
VIN
Feedback Voltage Accuracy
Min
Typ
8
Max
Units
40
V
7
V
VUVLO
Input Voltage Rising
VUVLO_YHS
Input Voltage Falling
1
V
VOUT=5V, No load
3
mA
0.8
V
Standby Current
Feedback Voltage
Test Condition
VFB
∆VFB
-1.5
+1.5
%
TSS
10
mS
RDS(ON)_HI
120
mΩ
High Site Switch Current Limit
ICL_HI
4.5
A
Max. Duty Cycle
DMAX
85
%
Switching Frequency
fOSC
Thermal Shutdown
TSD
Internal Soft Start Time
Hith Site Switch ON-Resistance
Thermal Shutdown Hysteresis
VFB=0.8V
175
∆TSD
Output OVP
VOV-OUT
Input OVP
VOV-IN
200
KHz
150
o
C
20
o
C
VOUT x
1.06
32
225
35
VOUT x
1.16
V
40
V
Input OVP Hysteresis
2
V
Short Current Limit
2
A
Rev. A.02
5
AME
40V 3.5A Buck Converter
AME5235
n Detailed Description
Under Voltage Lockout (UVLO)
The AME5235 incorporates an under voltage lockout
circuit to keep the device disabled when VIN (the input
voltage) is below the UVLO rising threshold voltage. Once
the UVLO rising threshold voltage is reached,the device
start-up begins. The device operates until VIN falls below
the UVLO falling threshold voltage. The typical hysteresis in the UVLO comparator is 1V.
Over Voltage Protection
The AME5235 has input and output over-voltage protections. The thresholds of input and output OVP circuit
include are typicapl 35V and minimum 106% x VOUT, respectively. Once the input voltage or output voltage is
higher than the threshold, the high-side MOSFET is turned
off. When the input voltage or output voltage drops lower
than the threshold, the high-side MOSFET will be enabled again.
Over Current Protection
The AME5235 cycle-by-cycle limits the peak inductor
current to protect embedded switch from dameage. Highside switch current limiting is implemented by monitoring the current through the high side MOSFET.
Thermal Shutdown
The AME5235 protects itself from overheating with an
internal thermal shutdown circuit. If the junction temperature exceeds the thermal shutdown trip point, the highside MOSFET is turned off. The part is restarted when
the junction temperature drops 20oC below the thermal
shutdown trip point
Setting the Output Voltage
The output voltage is using a resistive voltage divider
connected from the output voltage to FB. It divides the
output voltage down to the feedback voltage by the ratio:
VFB = Vout ×
6
R2
R1 + R2
the output voltage is:
Vout = 0.8 ×
R1 + R2
R2
Inductor Selection
The inductor is required to supply contant current to
the load while being driven by the switched input voltage.
A larger value inductor will have a larger physical size
and higher series resistance. It will result in less ripple
current that will in turn result in lower output ripple voltage. Make sure that the peak inductor current is below
the maximum switch current limit. Determine inductance
is to allow the peak-to-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 s × ∆I L
Vin
Where fS is the switching frequency, VIN is the input
voltage, VOUT is the output voltage, and ∆ΙL is the peakto-peak inductor ripple current. Choose an inductor that
will not saturate under the maximum inductor peak current, calculated by:
I LPK = I LOAD +
Vout
V
× 1 − out
2 × fs × L
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.
Input Capacitor
The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the
AC current while maintaining the DC input voltage. Use
low ESR capacitors 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.
Rev. A.02
AME
40V 3.5A Buck Converter
AME5235
Since the input capacitor (C1) absorbs the input switching current, it requires an adequate ripple current tating.
The RMS current in the input capacitor can be esimated
by:
I C1 = I LOAD ×
Vout
V
× 1 − out
Vin
Vin
At VIN=2VOUT, where IC1 = 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. 0.1µF, should be
placed as close to the IC as possible. The input voltage
ripple for low ESR capacitors can be estimated by:
I C1 =
I LOAD Vout
V
×
× 1 − out
C1× f s Vin
Vin
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor (C2) is required to maintain the
DC output voltage. Ceramic, tantalum, or low ESR
electrolutic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple
low. The output voltage ripple can be estimated by:
∆Vout =
Vout
V
1
× 1 − out × RESR +
fs × L
Vin
8× fs × C 2
Where RESR is the equivalent series resistance (ESR)
value of the output capacitor and C2 is the output capacitance value.
When using ceramic capacitors, the impandance 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 =
Rev. A.02
Vout
V
× 1 − out
8× f × L × C2
Vin
2
s
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 =
Vout
V
× 1 − out × RESR
fs × L
Vin
The characteristics of the output capacitor also affect
the stability of the regulation system.
Rectifier Diode
Use a Schottky diode as the rectifier to conduct current when the High-Side MOSFET is turned off. The
Schottky diode must have current rating higher than the
maximum output current and a reverse voltage rating
higher than the maximum input voltage.
Compensation Components
AME5235 has current mode control for easy compensation and fast transient response. The system stability
and transient response are controlled through the COMP
pin. COMP is the output of the internal transconductance
error amplifier. A series capacitor-resistor combination
sets a pole-zero combination to govern the characteristics of the control system. The DC gain of the voltage
feedback loop is given by:
AVDC = RLOAD × GCS × AEA ×
VFB
Vout
Where VFB is the feedback voltage (0.8V), AVEA is the
error amplifier voltage gain, GCS is the current sense
transconducductance and RLOAD is the load resistor value.
The system has two poles of importance. One is due to
the output capacitor and the load resistor, and the other
is due to the compansation capacitor (C4) and the output
resistor of the error amplifier. These poles are located at:
f P1 =
GEA
2 × π × C 4 × AVEA
fP2 =
1
2 × π × C 2 × RLOAD
7
AME
40V 3.5A Buck Converter
AME5235
Where GEA is the error amplifier transconducductance.
The system has one zero of importance, due to the compensation capacitor (C4) and the compensation resistor
(R3). This zero is located at:
1
2 × π × C 4 × R3
f Z1 =
The system may have another zero of importance, if
the output capacitor has a large capacitance and/or a high
ESR value. The zero, due to the ESR and capacitance of
the output capacitor, is located at:
f ESR
1
=
2 × π × C 2 × RESR
In this case, a third pole set by the second compensation capacitor (C5) and the compensation resistor (R3) is
used to compensate the effect of the ESR zero on the
loop gain. This pole is located at:
f P3 =
1
2 × π × C 5 × R3
The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The
system crossover frequency where the feedback loop has
the unity gain is important. Lower crossover frequencies
result in slower line and load transient responses, while
higher crossover frequencies could cause system instability. A good standard is to set the crossover frequency
below one-tenth of the switching frequency. To optimize
the compensation components, the following procedure
can be used.
2. Choose the compensation capacitor (C4) to achieve
the desired phase margin. For applications with typical
inductor values, setting the compensation zero (fZ1) below one-forth of the crossover frequency provides sufficient phase margin.
Determine C4 by the floolwing equation:
C4 >
4
2 × π × R3 × f c
Where R3 is the compensation resistor.
3. Determine if the second compensation capacitor (C5)
is required. It is required if the ESR zero of the output
capacitor is located at less than half of the switching
frequency, or the following relationship is valid:
1
f
< s
2 × π × C 2 × RESR 2
If this is the case, then add the second compensation
capacitor (C5) to set the pole fP3 at the location of the
ESR zero. Determine C5 by the equation:
C5 =
C 2 × RESR
R3
1. Choose the compensation resistor (R3) to set the
desired crossover frequency.
Determine R3 by the following equation:
R3 =
2 × C 2 × f c Vout 2 × C 2 × 0.1× f c Vout
×
<
×
GEA × GCS VFB
GEA × GCS
VFB
Where fC is the desired crossover frequency which is
typically below one tenth of the switching frequency.
8
Rev. A.02
AME
40V 3.5A Buck Converter
AME5235
PC Board Layout Guidance
When laying out the printed circuit board, the following checklist should be uesd to ensure proper operation of the IC.
1) Arrange the power components to reduce the AC loop size consisting of CIN, IN pin, SW pin and the sckottky diode.
2) Place input decoupling ceramic capacitor CIN as close to IN pin as possible. CIN is connected power GND with vias or
short and wide path.
3) Return FB and COMP to signal GND pin, and connect the singal GND to power GND at a single point for the best
noise immunity. Connect exposed pad to power ground copper area with copper and vias.
4) Use copper plane for power GND for best heat disspation and noise immunity.
5) Please feedback resistor close to FB pin.
Top Layer
Bottom Layer
Rev. A.02
9
AME
AME5235
40V 3.5A Buck Converter
n Radiated EMI Data (Vertical)
n Radiated EMI Data (Horizontal)
10
Rev. A.02
AME
40V 3.5A Buck Converter
AME5235
n Characterization Curve
Power ON from VIN
Efficiency vs. Output Current
100
95
Efficiency (%)
90
85
80
75
70
65
60
0.0
0.5
1.0
1.5
2.0
2.5
3. 0
3.5
Output Current (A)
Power Off from VIN
Full Load Ripple
Load Transient Response
Load Transient Response
0.5A to 1A
Rev. A.02
1A to 1.5A
11
AME
40V 3.5A Buck Converter
AME5235
n Characterization Curve (Contd.)
Load Transient Response
1.5A to 2.4A
0A Short
VOUT
(5V/div)
VSW
(10V/div)
IL
(1A/div)
Time(100µs/div)
3.5A Short
VOUT
(5V/div)
VSW
(10V/div)
IL
(2A/div)
Time(200µs/div)
12
Rev. A.02
AME
40V 3.5A Buck Converter
AME5235
n Characterization Curve
VFB VS Temperature
Stanby Current vs. Temperature
5.00
Standby Current (mA)
0.82
VFB(V)
0.81
0.80
0.79
0.78
-40
-20
0
20
40
Temperature(°C)
60
80
4.00
3.00
2.00
1.00
0.00
-40
100
Frequency vs. Temperature
-20
0
20
40
60
Temperature (°C)
80
100
Input OVP vs. Temperature
300 .0
40.0
38.0
250 .0
Input OVP (V)
Frequency (KHz)
39.0
200 .0
37.0
36.0
35.0
34.0
33.0
150 .0
32.0
31.0
100 .0
-40
30.0
-20
0
20
40
60
Temperature (°C)
Rev. A.02
80
100
-40
-20
0
20
40
60
80
100
Temperature (°C)
13
AME
40V 3.5A Buck Converter
AME5235
n Tape and Reel Dimension
SOP-8/PP
P
PIN 1
W
AME
AME
Carrier Tape, Number of Components Per Reel and Reel Size
Package
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
SOP-8/PP
12.0±0.1 mm
4.0±0.1 mm
2500pcs
330±1 mm
n Package Dimension
SOP-8/PP
TOP VIEW
SIDE VIEW
D1
E1
E2
E
L1
C
PIN 1
D
A1
14
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
1.350
1.750
0.053
0.069
A1
0.000
0.250
0.000
0.010
A2
1.250
1.650
0.049
0.065
C
0.100
0.250
0.004
0.010
E
3.750
4.150
0.148
0.163
E1
5.700
6.300
0.224
0.248
L1
0.300
1.270
0.012
0.050
b
0.310
0.510
0.012
0.020
D
4.720
5.120
0.186
0.202
e
e
FRONT VIEW
A
A2
b
SYMBOLS
1.270 BSC
0.050 BSC
θ
0o
8o
0o
8o
E2
1.940
2.600
0.076
0.102
D1
1.940
3.500
0.076
0.138
Rev. A.02
www.ame.com.tw
E-Mail: [email protected]
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. , June 2013
Document: A016A-DS5235-A.02
Corporate Headquarter
AME, Inc.
8F, 12, WenHu St., Nei-Hu
Taipei 114, Taiwan .
Tel: 886 2 2627-8687
Fax: 886 2 2659-2989
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