HOLTEK HT7466

HT7466
3A Step-Down DC to DC Converter
Feature
General Description
• Input voltage range: 4.75V to 24V
The HT7466 is a DC-DC buck regulator. The builtin high driver NMOS provides a monolithic solution
for high efficiency step-down DC-DC converter. With
3A output current, the wide input voltage range and
stable output voltage regulation can widely use in all
kinds of application, like communication, power for
high power LED, battery charger, etc. The protection
function include over current and over temperature
protection. The soft start function prevent inrush
supply current and output overshoot when initial
startup. The under voltage lockout is set to 4.1V. It
prevents abnormal situation occurring.
• Variable output voltage range: 1.222V to 20V
• 3A output current
• Efficiency up to 91%
• Fixed 380kHz operating frequency
• 20mA shutdown current
• Internal power MOSFET switch
• Stable operation using low ESR ceramic capacitors
• Over temperature protection
• Cycle-by-cycle over current protection
The HT7466 requires a minimum number of standard
external components and is available in a 8-pin SOP
package for small area PCB application.
• Soft-start function
• Under voltage lockout protection
• 8-pin SOP package
Applications
• Battery chargers
• Distributed power systems
• LED power supplies
• DSL modems
• Linear regulator pre power processing
• Set-Top-Boxes, DVD players, LCD displays
Application Circuit
VIN
4.75~24V
Efficiency vs Output Current
10nF
C2
10uF
C1
VIN
EN
BS
HT7466
SS
10nF
C3
SW
B330A
FB
GND
 R + R2 

VOUT = VFB ×  1
 R2 
L
VOUT
COMP
R1
R3
C5
R2
22uF
C6
C4
Rev. 1.00
1
September 02, 2011
HT7466
Block Diagram
Pin Assignment
Pin Description
Pin No. Pin Name
Description
1
SS
Soft-start input.
If the soft start function is to be used then an external capacitor should be connected between
this pin and ground. If the soft start function is not required the pin should be left open.
2
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.
3
VIN
Power supply input.
The input supply pin for the device, VIN, is connected to a supply voltage between 4.75V to
24V.
4
SW
Power switching output.
The internal power MOS drain is connected to the inductor, diode and VIN.
5
GND
6
FB
7
COMP
8
EN
Rev. 1.00
Ground.
Device ground voltage reference.
Feedback pin.
The feedback pin is connected to an external resistor divider to measure the output voltage.
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. The COMP pin value is 1.222V.
Enable input.
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.
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HT7466
Absolute Maximum Ratings
Maximum Input Supply Voltage.............................26V
Comp Voltage............................................................6V
Switch Node Voltage...............................................26V
SS Voltage.................................................................6V
Feedback Voltage......................................................6V
Maximum Junction Temperature........................ 150°C
EN Voltage................................................................6V
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
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
1.194
1.222
1.250
V
VFB
Feedback Voltage
VUVLO
Under Voltage Lockout Threshold
—
—
4.1
—
V
—
Under Voltage Lockout Threshold Hysteresis
—
—
200
—
mV
IQ
Quiescent Current
VFB=1.5V, VEN=High
—
1.0
1.2
mA
ISS
Shutdown Supply Current
VEN=0V
—
20
30
mA
FOSC
Oscillator Frequency
—
380
—
kHz
—
Short Circuit Frequency
VFB=0V
20
35
50
kHz
DMAX
Maximum Duty Cycle
VFB=1.0V
—
90
—
%
ISW
Upper Switch Leakage
VEN=0V, VSW=0V
—
0
10
mA
RDS
Switch On Resistance (note 2)
IOUT=3A
—
95
—
mW
ILIMIT
Current Limit
—
—
4.3
—
A
—
Error Amplifier Voltage Gain (note 2)
—
—
70
—
dB
—
Error Amplifier Trans-conductance (note 2)
—
—
800
—
mA/V
VEN
Enable Threshold
0.9
1.0
1.5
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. Designer test specifications.
Rev. 1.00
3
September 02, 2011
HT7466
Functional Description
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 4.3A,
the MOSFET oscillator frequency will be transformed
from 380kHz to a short circuit frequency of 35kHz
and the output current will remain at its current limit
value.
Setting the Output Voltage
The HT7466 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
1.222 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:
Over Temperature Protection
A thermal shutdown is implemented to prevent
damage due to excessive heat and power dissipation.
Typically the thermal shutdown threshold is 150°C.
The thermal shutdown is triggered the device stops
switching and when the device thermal falls until the
temperature hysteresis windows the device will be
starts switching again.
Application Information
Where R2 is the resistor divider lower resistor and R1
is the upper resistor, and the R1, R2 must be kW level.
Inductor
Compensation Components
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:
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.
• The inductor value
• DCR - copper wire resistance
Table 1 Compensation Values for Typical Output
Voltage/Capacitor Combinations.
VOUT
L
R3
C4
R1
R2
C6
C5
2.5V
15mH
3.9kW
5.6nF
10.5kW
10kW
22mF Ceramic
—
3.3V
15mH
4.7kW
4.7nF
17.0kW
10kW
22mF Ceramic
—
5.0V
15mH
7.5kW
2.7nF
30.9kW
10kW
22mF Ceramic
—
• The saturation current
Inductor choice is especially important as it is
important to ensure the inductor does not saturate
under its peak current conditions, the general
rule of keeping the inductor current peak-to-peak
ripple approximately 30% of the nominal output
current. Using this value of ripple current is a good
compromise between excessive output voltage ripple
and excessive component size and cost. Also ensure
that the inductor has a low DCR to minimize power
losses.
Bootstrap Circuit
In this device bootstrap capacitor is connected from
SW to BS pin, the Step-Down converter is use
N-Channel MOSFET, and MOS source pin is floating
to ground, this drive circuit of the application is
called high-side circuit, and the drive circuit used
in this kind of situation is called bootstrap circuit.
Large capacitor values can keep internal high-side
N-Channel MOSFET gate voltage greater than zero
when power MOS is turn on; usually a 10nF capacitor
is sufficient for most applications.
Rev. 1.00
Input/Output Capacitor
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 (in PCB layout C1 and C8 is parallels
input capacitor) 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.
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September 02, 2011
HT7466
A recommended PCB layout with component
locations is shown below.
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.
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 be
greater than the maximum input voltage.
• Short recovery time and low forward voltage -- use
a schottky diode type.
Top Layer
• Diode current rating should be greater than the
maximum load current.
Layout Considerations
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 close 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).
Bottom Layer
• A full ground plane is always helpful for better
EMI performance.
Rev. 1.00
5
September 02, 2011
HT7466
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 (http://www.holtek.com.tw/english/
literature/package.pdf) for the latest version of the package information.
8-pin SOP (150mil) Outline Dimensions for Thermally Enhanced Variations Only
(Exposed Pad)
MS-012
Symbol
A
Nom.
―
0.236
0.154
Max.
B
―
C
0.012
―
C'
―
0.193
D
―
―
0.067
D1
0.059
―
―
E
―
0.050
―
E2
0.039
―
―
F
―
―
0.006
G
0.016
―
0.050
H
0.004
―
0.010
α
0°
―
8°
Symbol
Rev. 1.00
Dimensions in inch
Min.
0.020
Dimensions in mm
Min.
Nom.
Max.
A
―
6.00
―
B
―
3.90
―
0.51
C
0.31
―
C'
―
4.90
―
D
―
―
1.70
D1
1.50
―
―
E
―
1.27
―
E2
1.00
―
―
F
―
―
0.15
G
0.40
―
1.27
H
0.10
―
0.25
α
0°
―
8°
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September 02, 2011
HT7466
Reel Dimensions
SOP 8N (150mil)
Symbol
Description
A
Reel Outer Diameter
Dimensions in mm
330.0±1.0
B
Reel Inner Diameter
100.0±1.5
C
Spindle Hole Diameter
13.0 +0.5/-0.2
D
Key Slit Width
T1
Space Between Flange
T2
Reel Thickness
Rev. 1.00
2.0±0.5
12.8 +0.3/-0.2
18.2±0.2
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September 02, 2011
HT7466
Carrier Tape Dimensions
 SOP 8N (150mil)
Symbol
Description
W
Carrier Tape Width
P
Cavity Pitch
E
Perforation Position
Dimensions in mm
12.0+0.3/-0.1
8.0±0.1
1.75±0.10
F
Cavity to Perforation (Width Direction)
5.5±0.1
D
Perforation Diameter
1.55±0.1
D1
Cavity Hole Diameter
1.50 +0.25/-0.00
P0
Perforation Pitch
4.0±0.1
P1
Cavity to Perforation (Length Direction)
2.0±0.1
A0
Cavity Length
6.4±0.1
B0
Cavity Width
5.2±0.1
K0
Cavity Depth
2.1±0.1
t
Carrier Tape Thickness
C
Cover Tape Width
Rev. 1.00
0.30±0.05
9.3±0.1
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September 02, 2011
HT7466
Holtek Semiconductor Inc. (Headquarters)
No.3, Creation Rd. II, Science Park, Hsinchu, Taiwan
Tel: 886-3-5631999
Fax: 886-3-563-1189
http://www.holtek.com.tw
Holtek Semiconductor Inc. (Taipei Sales Office)
4F-2, No. 3-2, YuanQu St., Nankang Software Park, Taipei 115, Taiwan
Tel: 886-2-2655-7070
Fax: 886-2-2655-7373
Fax: 886-2-2655-7383 (International sales hotline)
Holtek Semiconductor Inc. (Shenzhen Sales Office)
5F, Unit A, Productivity Building, No.5 Gaoxin M 2nd Road, Nanshan District, Shenzhen, China 518057
Tel: 86-755-8616-9908, 86-755-8616-9308
Fax: 86-755-8616-9722
Holtek Semiconductor (USA), Inc. (North America Sales Office)
46729 Fremont Blvd., Fremont, CA 94538, USA
Tel: 1-510-252-9880
Fax: 1-510-252-9885
http://www.holtek.com
Copyright © 2011 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.tw.
Rev. 1.00
9
September 02, 2011