HT1541A
1.3MHz Boost Converter
DESCRIPTION
FEATURES
The HT1541 is a current mode step up
converter intended for small, low power
applications. The HT1541 switches at 1.3MHz
and allows the use of tiny, low cost capacitors
and inductors 2mm or less in height. Internal
soft start results in small inrush current and
extends battery life. The HT1541 operates from
an input voltage as low as 2.5V and can
generate 12V at up to 300mA from a 5V supply.
The HT1541 includes under-voltage lockout,
current limiting, and thermal overload protection
to prevent damage in the event of an output
overload. The HT1541 is available in a small
5-pin TSOT23 package or QFN-8 (2mmX2mm)
package.
TYPICAL APPLICATION
On Board Power MOSFET
Uses Tiny Capacitors and Inductors
1.3MHz Fixed Switching Frequency
Internally Compensated
Internal Soft-Start
Operates with Input Voltage as Low as 2.5V
and Output Voltage as High as 22V
12V at 300mA from 5V Input
UVLO, Thermal Shutdown
Internal Current Limit
Available in a TSOT23-5 Package or QFN-8
(2mmX2mm) Package
APPLICATIONS
Camera Phone Flash
Handheld Computers and PDAs
Digital Still and Video Cameras
External Modems
Small LCD Displays
White LED Driver
Efficiency vs Load Current
100
95
VIN = 5V
HT1541A
EFFICIENCY (%)
90
85
80
VIN = 3.3V
75
70
VIN = 4.2V
65
60
55
50
VOUT = 12V
0
75 150 225 300 375 450
LOAD CURRENT (mA)
Rev. 01
HT1541A
PACKAGE REFERENCE
TOP VIEW
SW
1
GND
2
FB
3
5
IN
4
EN
TSOT23-5
QFN-8 (2mmX2mm)
(4)
ABSOLUTE MAXIMUM RATINGS (1)
Thermal Resistance
SW Pin ........................................... –0.3V to 25V
All Other Pins ................................ –0.3V to 6.5V
Junction Temperature ...............................150°C
(2)
Continuous Power Dissipation (TA = +25°C)
TSOT23-5 ................................................ 0.47W
QFN-8 (2mmx2mm) ................................. 1.56W
Lead Temperature ....................................260°C
Storage Temperature .............. –65°C to +150°C
TSOT25 ................................. 220 .... 110.. C/W
QFN-8 (2mmX2mm) ............... 80 ...... 16... C/W
Recommended Operating Conditions
(3)
Supply Voltage VIN ............................. 2.5V to 6V
Output Voltage VOUT ............................ 3V to 22V
Operating Temperature............. –40°C to +85°C
Maximum Junction Temp. (TJ) ............. +125°C
θJA
θJC
Notes:
1) Exceeding these ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/θJA. Exceeding the maximum allowable power dissipation
will cause excessive die temperature, and the regulator will go
into thermal shutdown. Internal thermal shutdown circuitry
protects the device from permanent damage.
3) The device is not guaranteed to function outside of its
operating range.
4) Measured on JESD51-7 4-layer board.
Rev. 01
HT1541A
ELECTRICAL CHARACTERISTICS
VIN = VEN = 5V, TA = +25C unless otherwise specified.
Parameters
Symbol
Operating Input Voltage
Condition
VIN
Min
Typ
2.5
Undervoltage Lockout
2.25
Undervoltage Lockout
Hysteresis
92
Max
Units
6
V
2.45
V
mV
Supply Current (Shutdown)
VEN = 0V
0.1
1
µA
Supply Current (Quiescent)
VFB = 1.3V
635
850
µA
1.0
1.3
1.6
MHz
Switching Frequency
fSW
Maximum Duty Cycle
VFB = 0V
80
85
EN Threshold
VEN Rising
1.0
1.3
EN Threshold
VEN Rising, VIN = 2.5V
EN Hysteresis
EN Input Bias Current
FB Voltage
FB Input Bias Current
(5)
SW On-Resistance
VFB = 1.25V
RDS (ON)
SW Current Limit (5)
SW Leakage
Thermal Shutdown
V
V
100
mV
1
µA
1.29
V
1.21
1.25
–100
–30
nA
0.65
Ω
1.9
A
VSW = 15V
(5)
1.6
1.1
VEN = 0V, 6V
VFB
%
1
160
µA
C
Note:
5) Guaranteed by design.
Rev. 01
HT1541A
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency vs
Temperature
1.252
1.40
1.250
1.35
FREQUENCY (MHz)
FEEDBACK VOLTAGE (V)
Feedback Voltage vs
Temperature
1.248
1.246
1.244
1.242
-50
0
50
100
TEMPERATURE (°C)
1.30
1.25
1.20
1.15
-50
150
640
84.0
635
83.9
630
83.8
625
83.7
620
83.6
615
610
-50
150
0.80
1.6
0.75
1.5
0.70
0.65
0.60
0.55
0.50
0
50
100
TEMPERATURE (°C)
150
Current Limit vs
Duty Cycle
RDS (ON) vs
Input Voltage
CURRENT LIMIT (A)
MAXIMUM DUTY CYCLE (%)
84.1
0
50
100
TEMPERATURE (°C)
150
Supply Current vs
Temperature
Maximum Duty Cycle vs
Temperature
83.5
-50
0
50
100
TEMPERATURE (°C)
1.4
1.3
1.2
1.1
2
3
4
5
INPUT VOLTAGE (V)
6
1.0
30
40
50
60
70
DUTY CYCLE (%)
80
Rev. 01
HT1541A
PIN FUNCTIONS
Pin #
TSSOT
QFN
Name
Function
Power Switch Output. SW is the drain of the internal MOSFET switch. Connect
the power inductor and output rectifier to SW. SW can swing between GND and
22V.
1
8
SW
2
1,4
GND
3
5
FB
Feedback Input. FB voltage is 1.25V. Connect a resistor divider to FB.
4
3
EN
Regulator On/Off Control Input. A high input at EN turns on the converter, and a
low input turns it off. When not used, connect EN to the input source for
automatic startup. The EN pin cannot be left floating.
5
2
IN
Input Supply Pin. Must be locally bypassed.
N.A
6,7
N/C
Ground.
Do not connect. Reserved for factory use.
OPERATION
The HT1541 uses a fixed frequency, peak current
mode boost regulator architecture to regulate
voltage at the feedback pin. The operation of the
HT1541 can be understood by referring to the
block diagram of Figure 1. At the start of each
oscillator cycle the MOSFET is turned on through
the control circuitry. To prevent sub-harmonic
oscillations at duty cycles greater than 50 percent,
a stabilizing ramp is added to the output of the
current sense amplifier and the result is fed into
the negative input of the PWM comparator. When
this voltage equals the output voltage of the error
amplifier the power MOSFET is turned off. The
voltage at the output of the error amplifier is an
amplified version of the difference between the
1.25V bandgap reference voltage and the
feedback voltage. In this way the peak current
level keeps the output in regulation. If the
feedback voltage starts to drop, the output of the
error amplifier increases. This results in more
current to flow through the power MOSFET, thus
increasing the power delivered to the output.
The HT1541 has internal soft start to limit the
amount of input current at startup and to also
limit the amount of overshoot on the output. The
current limit is increased by a fourth every 40s
giving a total soft start time of 120s.
CC
RC
SW
1
FB
3
+
+
-
1.25V
ERROR
AMPLIFIER
CONTROL
LOGIC
M1
PWM
COMPARATOR
+
+
-
1.3MHz
OSC
CURRENT
SENSE
AMPLIFIER
2
GND
Figure 1—Functional Block Diagram
Rev. 01
HT1541A
APPLICATIONS INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
Set the output voltage by selecting the resistive
voltage divider ratio. Use 11.8kΩ for the lowside resistor R2 of the voltage divider.
Determine the high-side resistor R1 by the
equation:
R1
R2VOUT - VFB
VFB
where VOUT is the output voltage.
For R2 = 11.8kΩ and VFB = 1.25V, then
R1 (kΩ) = 9.44kΩ (VOUT – 1.25V).
Selecting the Input Capacitor
An input capacitor is required to supply the AC
ripple current to the inductor, while limiting noise
at the input source. This capacitor must have low
ESR, so ceramic is the best choice.
Use an input capacitor value of 4.7μF or greater.
This capacitor must be placed physically close
to the IN pin. Since it reduces the voltage ripple
seen at IN, it also reduces the amount of EMI
passed back along that line to the other circuitry.
Selecting the Output Capacitor
A single 4.7F to 10F ceramic capacitor
usually provides sufficient output capacitance
for most applications. If larger amounts of
capacitance is desired for improved line support
and transient response, tantalum capacitors
can be used in parallel with the ceramic. The
impedance of the ceramic capacitor at the
switching frequency is dominated by the
capacitance, and so the output voltage ripple is
mostly independent of the ESR. The output
voltage ripple VRIPPLE is calculated as:
VRIPPLE
input voltage. Choose an inductor that does not
saturate at the SW current limit. A good rule for
determining the inductance is to allow the peakto-peak ripple current to be approximately 30%50% of the maximum input current. Make sure
that the peak inductor current is below 75% of
the typical current limit at the duty cycle used to
prevent loss of regulation due to the current
limit variation.
Calculate the required inductance value L using
the equations:
L
VIN (VOUT - VIN )
VOUT fSW I
IIN(MAX )
VOUT ILOAD (MAX )
VIN
I 30% 50%IIN(MAX )
Where ILOAD(MAX) is the maximum load current, ∆I
is the peak-to-peak inductor ripple current, and η
is efficiency. For the MP1541, 4.7µH is
recommended for input voltages less than 3.3V
and 10µH for inputs greater than 3.3V.
Selecting the Diode
The output rectifier diode supplies current to the
inductor when the internal MOSFET is off. To
reduce losses due to diode forward voltage and
recovery time, use a Schottky diode. Choose a
diode whose maximum reverse voltage rating is
greater than the maximum output voltage. For
output voltage less than 20V, it is recommended
to choose the MBR0520 for most applications.
This diode is used for load currents less than
500mA. If the average current is more than
500mA the Microsemi UPS5817 is a good choice.
ILOAD VO UT VIN
VO UT C2 f SW
Where VIN is the input voltage, ILOAD is the load
current, C2 is the capacitance of the output
capacitor, and fSW is the 1.3MHz switching
frequency.
Selecting the Inductor
The inductor is required to force the output
voltage higher while being driven by the lower
Rev. 01
HT1541A
Compensation
The HT1541 uses an amplifier to compensate
the feedback loop rather than a traditional
transconductance amplifier like most current
mode regulators. Frequency compensation is
provided by an internal resistor and capacitor
along with an external resistor. The system
uses two poles and one zero to stabilize the
control loop. The poles are fP1 set by the output
capacitor and load resistance, and fP2 set by the
internal compensation capacitor Cc, the gain of
the error amplifier and the resistance seen
looking out at the feedback node REQ. The zero
fZ1 is set internally around 20kHz. These are
determined by the equations:
fP1
fP 2
1
C2 R LOAD
1
2 7.9 10
9
R
EQ
Where RLOAD is the load resistance and REQ is:
Where R1, R2, and R3 are seen in Figure 2.
The DC loop gain is:
VIN R LOAD VFB
VOUT
2
There is also a right-half-plane zero (fRHPZ) that
exists in all continuous mode (inductor current
does not drop to zero on each cycle) step up
converters. The frequency of the right half plane
zero is:
2
fRHPZ
VIN R LOAD
2 L VOUT
1
1
2 C3 R4
1
1
1
R1 R2 R3
f Z2
(R1 R2)
R3
(R1 R2)
A VDC 500
For the HT1541 it is recommended that a 47kΩ
to 100kΩ resistor be placed in series with the FB
pin and the resistor divider as seen in Figure 2.
For most applications this is all that is needed for
stable operation. If greater phase margin is
needed a series resistor and capacitor can be
placed in parallel with the high-side resistor R1 as
seen in Figure 2. The pole and zero set by the
lead-lag compensation network are:
fP 3
f Z1 20kHz
R EQ
To stabilize the regulation control loop, the
crossover frequency (the frequency where the
loop gain drops to 0dB or a gain of 1, indicated
as fC) should be at least one decade below the
right-half-plane zero and should be at most
75kHz. fRHPZ is at its lowest frequency at
maximum output load current (RLOAD is at a
minimum) and minimum input voltage.
1
2 C3 R1 R4
LAYOUT CONSIDERATIONS
High frequency switching regulators require
very careful layout for stable operation and low
noise. All components must be placed as close
to the IC as possible. Keep the path between
L1, D1, and C2 extremely short for minimal
noise and ringing. C1 must be placed close to
the IN pin for best decoupling. All feedback
components must be kept close to the FB pin to
prevent noise injection on the FB pin trace. The
ground return of C1 and C2 should be tied
close to the GND pin. See the HT1541 demo
board layout for reference.
2
Rev. 01
HT1541A
TYPICAL APPLICATION CIRCUITS
HT1541A
Figure 2—VIN = 5V, VOUT = 12V, IOUT = 300mA Boost Circuit
HT1541A
Figure 3—Typical Application Circuit for Driving Flashlight LEDs
(20mA Torch Current, 100mA Flash Current)
Rev. 01
HT1541A
PACKAGE INFORMATION
SOT23-5(3mm*1.6mm)
Rev. 01
HT1541A
PACKAGE INFORMATION
QFN-8 (2mmX2mm)
PIN 1 ID
MARKING
1.90
2.10
0.25
0.45
0.18
0.30
1.90
2.10
PIN 1 ID
INDEX AREA
PIN 1 ID
SEE DETAIL A
0.45
0.65
8
1
1.05
1.25
0.50
BSC
5
TOP VIEW
4
BOTTOM VIEW
0.80
1.00
PIN 1 ID OPTION A
0.30x45º TYP.
PIN 1 ID OPTION B
R0.20 TYP.
0.20 REF
0.00
0.05
SIDE VIEW
DETAIL A
NOTE:
1.90
0.70
0.60
1) ALL DIMENSIONS ARE IN MILLIMETERS.
2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH.
3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETER MAX.
4) DRAWING CONFORMS TO JEDEC MO-229, VARIATION VCCD-3.
5) DRAWING IS NOT TO SCALE.
0.25
1.20
0.50
RECOMMENDED LAND PATTERN
Rev. 01
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