HT7465 Step-Down DC to DC Converter

HT7465
Step-Down DC to DC Converter
Feature
General Description
• Input voltage range: 4.75V to 24V
The HT7465 is a 2A high efficiency step-down DCDC converter which includes a fully integrated MOS
power transistor. The device uses a current-mode
control operating methodology and can operate over a
wide input voltage range of 4.75V to 24V for which it
can provide a stable adjustable output voltage.
• Variable output voltage range: 0.92V to 20V
• 2A output current
• Efficiency up to 92%
• Fixed 380kHz operating frequency
• 20mA shutdown current
The device includes over temperature protection,
over current protection and under voltage lockout
protection, features which combine to prevent device
damage due to overload conditions. In its shutdown
mode the regulator draws a mere 20uA of supply
current.
• Internal power MOSFET switch
• Stable operation using low ESR ceramic capacitors
• Over temperature protection
• Cycle-by-cycle over current protection
• Under voltage lockout protection
The device is available in 8-pin SOP package type
and provides a very compact system solution with a
minimum of external components.
• 8-pin SOP package
Applications
• Battery chargers
• Distributed power systems
• LED driver
• DSL modems
• Linear regulator pre power processing
• Set-Top-Boxes, DVD players, LCD displays
Application Circuits
VIN
4.75~24V
10nF
C2
10 F
C1
VIN
EN
BS
HT7465
GND
COMP
L
SW
VOUT
10/15 H
B230A
FB
R1
R3
C5
Efficiency vs Output Current
 R  R2 

VOUT  VFB   1
 R2 
R2
22uF
C6
C4
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HT7465
Block Diagram
EN
NC
Under-voltage
lockout
Regulator
VIN
Current Sense
Amplifier
Current
Sense
5V
+
BS
-
SCP
+
Control
Logic
OSC
240/380kHz
SW
PWM Comparator
-
Error
Amplifier
Soft-Start
+
GND
0.92V
FB
COMP
Pin Assignment
BS
VIN
SW
GND
1
2
3
4
8
PAD
(GND)
7
6
5
NC
EN
COMP
FB
HT7465
8 SOP-A
(Exposed Pad)
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HT7465
Pin Description
Pin No.
Pin Name
Description
1
BS
Internal Power NMOS Gate Drive Boost Input.
A 10nF or greater value capacitor should be connected from SW to BS for additional
Power NMOS gate driving purposes.
2
VIN
Power supply input.
The input supply pin for the device, VIN, is connected to a supply voltage between
4.75V to 24V.
3
SW
Power switching output.
The internal power MOS drain is connected to the inductor diode and VIN.
4
GND
5
FB
Feedback pin.
The feedback pin is connected to an external resistor divider to measure the output
voltage.
6
COMP
Error Amplifier Output.
Used for compensation of the regulation control loop. Connect a series RC network
from COMP to GND to compensate the regulation control loop and the COMP pin
value is 0.92V.
7
EN
Enable Input and dimming control.
This pin is set high to turn on the regulator and low to turn it off. The pin should be left
unconnected if not used.
8
NC
Not used
Exposed Pad
GND
Ground.
Device ground voltage reference.
Ground.
Device ground voltage reference.
Absolute Maximum Ratings
Maximum Input Supply Voltage.............................26V
EN Voltage................................................................6V
Switch Node Voltage...............................................26V
Comp Voltage............................................................6V
Feedback Voltage......................................................6V
Maximum Junction Temperature........................ 150°C
Note: These are stress ratings only. Stresses exceeding the range specified under “Absolute Maximum Ratings”
may cause substantial damage to the device. Functional operation of this device at other conditions beyond
those listed in the specification is not implied and prolonged exposure to extreme conditions may affect
device reliability.
Recommended Operating Conditions
Ambient Temperature Range................ -40°C ~ +85°C
Input Supply Voltage.................................4.75V ~ 24V
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HT7465
Electrical Characteristics
VIN=12V, Ta=25°C, unless otherwise specified refer to circuit of Figure 1. ( note 1)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
4.75V ≤ VIN ≤ 24V
0.892
0.920
0.948
V
VFB
Feedback Voltage
VUVLO
Under Voltage Lockout Threshold
—
—
4.1
—
V
—
Under Voltage Lockout Threshold Hysteresis
—
—
200
—
mV
IQ
Quiescent Current
VFB=1.2V, VEN=High
—
1.1
1.3
mA
ISS
Shutdown Supply Current
VEN=0V
—
20
30
mA
FOS
Oscillator Frequency
—
380
—
kHz
—
Short Circuit Frequency
VFB=0V
—
240
—
kHz
DMAX
Maximum Duty Cycle
VFB=0.6V
—
90
—
%
ISW
Switch Leakage
VEN=0V, VSW=0V
—
0
10
mA
RDS
Switch On Resistance (note 2)
IOUT=2A
—
0.18
—
W
ILIMIT
Current Limit
—
—
3.4
—
A
—
Error Amplifier Voltage Gain (note 2)
—
—
70
—
dB
—
Error Amplifier Trans-conductance (note 2)
—
—
800
—
mA/V
VEN
Enable Threshold
0.7
1.0
1.3
V
TJ
Thermal Shutdown
—
150
—
°C
—
4.75V ≤ VIN ≤ 24V
—
Note: 1. Specifications are production tested at Ta=room temperature. Specifications over the -40°C to 85°C
operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC).
2. The test specifications by designer.
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HT7465
Functional Description
triggered the device stops switching and will require
a power on input voltage signal, before resuming
switching operation.
Setting the Output Voltage
The HT7465 is a step down switching DC/DC
converter device. The device switching output, SW, is
connected to a standard converter LC filter circuit for
buck conversion. The output current is sensed using
an external voltage divider network connected to the
load output voltage and ground, and the sense voltage
feedback to the device on the FB pin. By comparing
this sense voltage with an internally generated
0.92 voltage reference, suitable regulation can be
implemented to achieve the required output voltage.
By selecting suitable values of external voltage
divider resistors, the desired output voltage can be
adjusted to the required level. The output voltage can
be calculated using the following formula:
Application Information
Inductor
The inductor is required to supply a constant current
to the output load while being driven by the switched
input voltage. The choice of inductor affects steady
state operation as well as transient behavior and
loop stability. There are three important electrical
parameters which need to be considered when
choosing an inductor:
• The inductor value
• DCR - copper wire resistance
R1+R2
VOUT=x0.92
R2
• The saturation current
Inductor choice is especially important as it is
important to ensure the inductor does not saturate
under its peak current conditions. Also ensure that the
inductor has a low DCR to minimise power losses.
where R2 is the resistor divider lower resistor and R1
is the upper resistor.
Compensation Components
Input/Output Capacitor
Care must be taken when selecting external
components. The COMP pin is the output of the
error amplifier and must be properly connected to an
external RC network to ensure regulator loop stability.
The values of the compensation components given
in Table 1 yield a stable control loop for the output
voltage and capacitor given.
Input Capacitor
Because the VIN pin is connected to the internal power
MOSFET, when the power MOSFET is switching and
the input current is discontinuous, therefore an input
capacitor C1 is required to supply the AC current
to the step-down converter while maintaining the
DC input voltage. A low ESR ceramic capacitor is
required to keep noise to a minimum.
Table 1 Compensation Values for Typical Output
Voltage/Capacitor Combinations.
VOUT
L
R3
C4
C6
C5
2.5
10/15mH
9.1K
2.2n
22mF Ceramic
—
3.3
10/15mH
10K
3.9n
22mF Ceramic
—
5.0
10/15mH
18K
1.5n
22mF Ceramic
—
Output Capacitor
The output capacitor is required to maintain the DC
output voltage. Ceramic or low ESR electrolytic
capacitors is the rule to choice of external load
capacitor is also critical and low ESR value capacitors
must be used to ensure stability. This capacitor must
be connected very close to the inductor, with short
traces for good noise performance.
Current Limit Protection
The device has a cycle-by-cycle current limit to
protect the internal power MOSFET. If the inductor
current reaches the current limit threshold of 3.4A,
the MOSFET oscillator frequency will be transformed
from 380kHz to a short circuit frequency of 240kHz
and the output current will remain at its current limit
value.
Schottky Diode
The output diode conducts when the internal power
MOSFET is switched off. There are three important
electrical parameters to consider when choosing the
diode:
• The diode maximum reverse voltage value must
greater than the maximum input voltage
Over — Temperature Protection
• Short recovery time -- use Schottky diode
A thermal shutdown function is implemented to
prevent damages due to excessive heat and power
dissipation. Typically the thermal shutdown threshold
temperature is 150°C.When the thermal shutdown is
Rev. 1.10
• Diode current rating should be greater than the
maximum load current
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HT7465
Layout Considerations
A recommended PCB layout with component
locations is shown below.
Circuit board layout is a very important consideration
for switching regulators if they are to function
properly. Poor circuit layout may result in related
noise problems. In order to minimise EMI and
switching noise, follow the guidelines below:
• All tracks should be as wide as possible.
• The input and output capacitors, C1 (C8) and C6
(C7), should be placed close to the VIN, VOUT
and GND pins (C1 and C8 is parallel; C6 and C7 is
parallel).
• The Schottky diode D and inductor L must be
placed closec to the SW pin.
• Feedback resistor, R1 (R1-1) and R2, must be
placed close to the FB and GND pins (R1 and R1-1
is series).
• A full ground plane is always helpful for better
EMI performance.
Top Layer
Bottom Layer
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HT7465
Package Information
Note that the package information provided here is for consultation purposes only. As this information may be
updated at regular intervals users are reminded to consult the Holtek website for the latest version of the package
information.
Additional supplementary information with regard to packaging is listed below. Click on the relevant section to be
transferred to the relevant website page.
• Further Package Information (include Outline Dimensions, Product Tape and Reel Specifications)
• Packing Meterials Information
• Carton information
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HT7465
8-pin SOP_EP (150mil) Outline Dimensions for Thermally Enhanced Variations Only
(Exposed Pad)
Symbol
Dimensions in inch
Min.
Nom.
Max.
A
―
0.236 BSC
―
B
―
0.154 BSC
―
C
0.012
―
0.020
C'
―
0.193 BSC
―
D
―
―
0.069
D1
0.059
―
―
E
―
0.050 BSC
―
E2
0.039
―
―
F
0.004
―
0.010
G
0.016
―
0.050
H
0.004
―
0.010
α
0°
―
8°
Symbol
Rev. 1.10
Dimensions in mm
Min.
Nom.
Max.
A
―
6.00 BSC
―
B
―
3.90 BSC
―
C
0.31
―
0.51
C'
―
4.90 BSC
―
D
―
―
1.75
D1
1.50
―
―
E
―
1.27 BSC
―
E2
1.00
―
―
F
0.10
―
0.25
G
0.40
―
1.27
H
0.10
―
0.25
α
0°
―
8°
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HT7465
Copyright© 2014 by HOLTEK SEMICONDUCTOR INC.
The information appearing in this Data Sheet is believed to be accurate at the time
of publication. However, Holtek assumes no responsibility arising from the use of
the specifications described. The applications mentioned herein are used solely
for the purpose of illustration and Holtek makes no warranty or representation that
such applications will be suitable without further modification, nor recommends
the use of its products for application that may present a risk to human life due to
malfunction or otherwise. Holtek's products are not authorized for use as critical
components in life support devices or systems. Holtek reserves the right to alter
its products without prior notification. For the most up-to-date information, please
visit our web site at http://www.holtek.com.
Rev. 1.10
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April 18, 2014