SP6656_06 Datasheet, PDF (11/16 Pages) Sipex Corporation – High Efficiency 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

THEORY OF OPERATION
when the load current is less than half the
inductor ripple current defined by K_ON/L.
Thermal Shutdown
The converter will open both power switches
if the die junction temperature rises above
140°C. The die must cool down below 126°C
before the regulator is re-enabled. This fea-
ture protects the SP6656 and surrounding
circuitry from excessive power dissipation
due to fault conditions.
Shutdown/Enable Control
The EN pin of the device is a logic level
control pin that shuts down the converter
when logic is low, or enables the converter
when logic is high. When the converter is
shut down, the power switches are opened
and all circuit biasing is extinguished leav-
ing only junction leakage currents on supply
pins 1 and 2. After pin 5 is brought high to
enable the converter, there is a turn on
delay to allow the regulator circuitry to rees-
tablish itself. Power conversion begins with
the assertion of the internal reference ready
signal which occurs approximately 150µs
after the enable signal is received.
Output Voltage Selection
The OVSI (Output Voltage Selection Input)
pin is internally driving a NMOS Gate which
Drain (OVSO pin) is used to short circuit R_S
and then achieve a higher output voltage (
see table 1 for calculation, page 3)
External Feedback Pin
The FB pin 6 is compared to an internal
reference voltage of 0.8V to regulate the
SP6656 output. The output voltage can be
externally programmed within the range
+1.0V to +5.0V by tying a resistor from FB to
ground and FB to V_OUT (pin7). See the
applications section for resistor selection
information.
APPLICATION INFORMATION
Inductance
(uH)
4.7
4.7
4.7
10
10
10
22
22
22
Capacitance
(uF)
10
10
4.7
4.7
Manufacturer/Part No.
Murata LQH32CN4R7M53L
Murata LQH31CN4R7M03L
Murata LQH2MCN4R7M02L
Murata LQH32CN100K53L
TDK RLF5018T-100MR94
Coilcraft LPO6013-103K
Murata LQH32CN220K21
TDK RLF5018T-220MR63
Coilcraft LPO6013-223K
Manufacturer/Part No.
TDK C2012X5R0J106M
Murata GRM21BR60J106KE01
TDK C2012X5R0J475M
Murata GRM21BR60J475KE01
INDUCTORS - SURFACE MOUNT
Inductor Specification
Series R Isat
Size
L x W Ht.
Inductor Type
ohms
(A)
(mm) (mm)
0.150
0.65 3.2x2.5 1.55 Unshielded Ferrite Core
0.65
0.34 3.2x1.6 1.8 Unshielded Ferrite Core
0.80
0.30 2.0x1.6 0.9 Unshielded Ferrite Core
0.300
0.45 3.2x2.5 1.55 Unshielded Ferrite Core
0.056
0.94 5.6x5.2 2.0
Shielded Ferrite Core
0.300
0.70 6.0x5.4 1.3 Unshielded Ferrite Core
0.710
0.25 3.2x2.5 2.0 Unshielded Ferrite Core
0.130
0.63 5.6x5.2 2.0
Shielded Ferrite Core
0.520
0.45 6.0x5.4 1.3 Unshielded Ferrite Core
CAPACITORS - SURFACE MOUNT
Capacitor Specification
Ripple
ESR Current
Size
Voltage Capacitor
ohms
(max)
(A) @
45C
L x W Ht.
(mm) (mm) (V)
Type
0.003
1.00 2.0x1.2 1.25 6.3
X5R Ceramic
0.003
1.00 2.0x1.2 1.25 6.3
X5R Ceramic
0.005
1.00 2.0x1.2 1.25 6.3
X5R Ceramic
0.005
1.00 2.0x1.2 1.25 6.3
X5R Ceramic
Manufacturer
Website
www.murata.com
www.murata.com
www.murata.com
www.murata.com
www.tdk.com
www.coilcraft.com
www.murata.com
www.tdk.com
www.coilcraft.com
Manufacturer
Website
www.tdk.com
www.murata.com
www.tdk.com
www.murata.com
Note: Components highlighted in bold are those used on the SP6656 Evaluation Board.
Table 2 Component Selection
Inductor Selection
The SP6656 uses a specially adapted mini-
mum on-time control of regulation utilizing a
precision comparator and bandgap refer-
ence. This adaptive minimum on-time con-
For the typical SP6656 application circuit with
inductor size of 10µH, and K_ON of 2V*µsec,
the SP6656 current ripple would be about
200mA, and would be fairly constant for differ-
ent input and output voltages, simplifying the
trol has the advantage of setting a constant
current ripple for a given inductor size.
From the operations section it has been shown:
selection of components for the SP6656 power
circuit. Other inductor values could be se-
lected, as shown in Table 2 Components
Inductor Current Ripple, I_LR ≈ ^KON
L
Selection. Using a larger value than 10µH in
an attempt to reduce output voltage ripple
would reduce inductor current ripple and may
Date: 3/6/06
SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output © Copyright 2006 Sipex Corporation
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