100mA PFM Synchronous
Step-up DC/DC Converter
Features
• Low start-up voltage: 0.7V (Typ.)
• High efficiency: 1.8V ≤ V
OUT
≤ 2.2V upper 80%,
2.7V ≤ V
OUT
≤ 5.0V upper 85% (Typ.)
• High output voltage accuracy: ±2.5%
• Output voltage: 1.8V, 2.2V, 2.7V, 3.0V, 3.3V, 3.7V,
5.0V
• Output current up to 100mA
• Ultra low supply current I
DD
: 4μA (Typ.)
• Low ripple and low noise
• Low shutdown current: 0.1μA (Typ.)
• TO92, SOT89, SOT23 and SOT23-5 package
HT77xxS
General Description
The HT77xxS devices are a high efficiency PFM syn-
chronous step-up DC-DC converter series which are
designed to operate with both wire wound chip power
inductors and also with multi-layered chip power
inductors. The device series have the advantages of
extremely low start-up voltage as well as high output
voltage accuracy. Being manufactured using CMOS
technology ensures ultra low supply current. Because
of their higher operating frequency, up to 500 kHz,
the devices have the benefits of requiring smaller out-
line type lower value external inductors and capaci-
tors. The higher operating frequency also offers the
advantages of much reduced audio frequency noise.
The devices require only three external components
to provide a fixed output voltage of 1.8V, 2.2V, 2.7V,
3.0V, 3.3V, 3.7V or 5.0V.
The HT77xxS devices include an internal oscillator,
PFM control circuit, driver transistor, reference volt-
age unit and a high speed comparator. They employ
pulse frequency modulation techniques, to obtain
minimum supply current and ripple at light output
loading. These devices are available in space saving
TO92, SOT89, SOT23 and SOT23-5 packages. For
SOT23-5 package types, they also include an internal
chip enable function to reduce power consumption
when in the shutdown mode.
Applications
• Palmtops/PDAs
• Portable communicators/Smartphones
• Cameras/Camcorders
• Battery-powered equipment
Selection Table
Part No.
HT7718S
HT7722S
HT7727S
HT7730S
HT7733S
HT7737S
HT7750S
Output Voltage
1.8V
2.2V
2.7V
3.0V
3.3V
3.7V
5.0V
±2.5%
TO92
SOT89
SOT23
SOT23-5
Tolerance
Package
Rev. 1.00
1
February 22, 2012
HT77xxS
Block Diagram
V O U T
V re f
P F M
C o n tro l
V O U T
L X
B u ffe r
O S C
C h ip E n a b le
G N D
C E
Pin Assignment
T O 9 2
S O T 8 9
S O T 2 3
V O U T
3
S O T 2 3 -5
L X
5
G N D
4
F r o n t V ie w
1
2
3
T o p V ie w
1
G N D V O U T L X
G N D
2
3
V O U T
T o p V ie w
1
G N D
2
L X
1
C E
2
V O U T
3
N C
L X
B o tto m
V ie w
G N D
G N D
V O U T
L X
L X
C E
V O U T
N C
Pin Description
Pin No.
TO92
—
2
—
1
3
SOT89
—
2
—
1
3
SOT23
—
3
—
1
2
SOT23-5
1
2
3
4
5
Pin Name
CE
VOUT
NC
GND
LX
Description
Chip enable pin, high active
DC/DC converter output monitoring pin
No connection
Ground pin
Switching pin
Rev. 1.00
2
February 22, 2012
HT77xxS
Absolute Maximum Ratings
Maximum Input Supply Voltage .......................... 6.5V
Ambient Temperature Range ............... -40°C to 85°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.
Storage Temperature .......................... -50°C to 125°C
Electrical Characteristics
Symbol
V
IN
ΔV
OUT
V
START
V
HOLD
I
DD
I
SHDN
V
IH
V
IL
I
LEAK
F
OSC
D
OSC
η
Parameter
Input Voltage
Output Voltage Tolerance
Starting Voltage
Voltage Hold
Supply Current
Shutdown Current
CE High Threshold
CE Low Threshold
LX Leakage Current
Oscillator Frequency
Oscillator Duty Cycle
Efficiency
Ta= 25°C; V
IN
= V
OUT
×0.6; I
OUT
= 10mA; unless otherwise specified
Test Conditions
—
V
IN
: 0 to 2V, I
OUT
= 1mA
V
IN
: 2 to 0V, I
OUT
= 1mA
V
S
= V
OUT
+0.5V, Measured at VOUT
Pin
CE= GND
—
V
S
= 5.5V, V
X
= 4V
Measurement at the LX pin
V
S
= V
OUT
×0.95
Measurement at the LX pin
1.8V≤ V
OUT
≤ 2.2V
2.7V≤ V
OUT
≤ 5.0V
Min.
—
-2.5
—
—
—
—
1.5
—
—
—
70
—
—
Typ.
—
—
0.7
0.7
4
0.1
—
—
0.05
500
80
80
85
Max.
6.0
+2.5
0.9
—
7
1.0
—
0.4
1
—
—
—
—
Unit
V
%
V
V
μA
μA
V
V
μA
kHz
%
%
%
Note: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating
Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific
performance limits. The guaranteed specifications apply only for the test conditions listed.
Rev. 1.00
3
February 22, 2012
HT77xxS
Application Circuits
Without CE Pin
V
IN
L
10μH
LX
VOUT
V
OUT
HT77xxS
C
IN
10μF
GND
C
OUT
10μF
With CE Pin
V
IN
L
10μH
LX
VOUT
V
OUT
C
IN
10μF
V
OUT
CE
HT77xxS
GND
C
OUT
10μF
V
IN
L
10μH
LX
VOUT
V
OUT
C
IN
10μF
CE
HT77xxS
GND
C
OUT
10μF
List of Components
Component
Reference
C
IN
, C
OUT
L
L
Part Number
GJ831CR61E106KE83L
SR0302100MLB
LBC3225T100MR
Manufacturer
Murata
ABC Taiwan Electronics Corp.
TAIYO YUDEN
Value
10μF, 25V. X5R Ceramic
10μH, R
DC
= 0.25Ω.
Wire Wound Chip Power Inductor
10μH, R
DC
= 0.133Ω.
Multi-layered Chip Power Inductor
Rev. 1.00
4
February 22, 2012
HT77xxS
Functional Description
The HT77xxS is a constant on time synchronous step-up
converter, which uses a pulse frequency modulation
(PFM) controller scheme. The PFM control scheme is
inherently stable. The required input/output capacitor
and inductor selections will not create situations of
instability.
The device includes a fully integrated synchronous
rectifier which reduces costs (includes reduce L and C
sizes, eliminates Schottky diode cost etc.) and board
area. A true load disconnect function ensures that the
device is completely shutdown.
Application Information
Inductor Selection
Selecting a suitable inductor is an important consider-
ation as it is usually a compromise situation between
the output current requirements, the inductor saturation
limit and the acceptable output voltage ripple. Lower
values of inductor values can provide higher output
currents but will suffer from higher ripple voltages
and reduced efficiencies. Higher inductor values can
provide reduced output ripple voltages and better
efficiencies, but will be limited in their output current
capabilities. For all inductors it must be noted however
that lower core losses and lower DC resistance values
will always provide higher efficiencies.
The peak inductor current can be calculated using the
following equation:
I
L
(
PEAK
)
=
V
OUT
×
I
O
V
IN
×
(
V
OUT
−
V
IN
)
+
V
IN
×
η
2
×
V
OUT
×
L
Low Voltage Start-up
The devices have a very low start up voltage down to
0.7V. When power is first applied, the synchronous
switch will be initially off but energy will be trans-
ferred to the load through its intrinsic body diode.
Shutdown
During normal device operation, the EN pin should be
either high or connected to the VOUT pin or the VIN
power source. When the device is in the shutdown
mode, that is when the EN pin is pulled low, the inter-
nal circuitry will be switched off. During shutdown,
the PMOS power transistor will be switched off thus
placing the output into a floating condition.
Where
V
IN
= Input Voltage
V
OUT
= Output Voltage
I
O
= Output Current
η = Efficiency
L = Inductor
Synchronous Rectification
A dead time exists between the N channel and P chan-
nel MOSFET switching operations. In synchronous
rectification, the P channel is replaced by a Schottky
diode. Here the P channel switch must be completely
off before the N channel switch is switched on. After
each cycle, a 30ns delay time is inserted to ensure the
N channel switch is completely off before the P channel
switch is switched on to maintain a high efficiency
over a wide input voltage and output power range.
Capacitor Selection
As the output capacitor selected affects both efficien-
cy and output ripple voltage, it must be chosen with
care to achieve best results from the converter. Output
voltage ripple is the product of the peak inductor current
and the output capacitor equivalent series resistance
or ESR for short. It is important that low ESR value
capacitors are used to achieve optimum performance.
One method to achieve low ESR values is to connect
two or more filter capacitors in parallel. The capacitors
values and rated voltages are only suggested values.
Rev. 1.00
5
February 22, 2012
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