SP6650 View Datasheet(PDF) - Signal Processing Technologies
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SP6650 Datasheet PDF : 17 Pages
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ADDITIONAL APPLICATION CIRCUITS: continued
SP6650 can also be configured with few external
components to achieve buck-boost voltage con-
version. Efficiency of 75% to 87% can often be
obtained depending on the load current and output
voltage. Figure 19 and Figure 20 demonstrate two
typical applications in which the USB input is
converted to a 12V and a well regulated 5V.
The operation of the circuit is as follows. When
the internal high side PMOS turns on, the LX pin
swings to the input voltage which turns on the
external NMOS Q1. A voltage equal to Vin is
then applied to the inductor to cause the inductor
current rise linearly. Since there’s no current
delivered to the output, the output capacitor is
discharged by the load current. Therefore, the
internal PMOS can be only turned off by the
over-current comparator since the loop com-
parator would never toggle during this state.
When the internal PMOS is open, the internal
low side NMOS is turned on. This pulls the LX
pin to the ground and turns off the Q1. As a
result, the Schottky D2 is forward biased and
conducts the inductor current to the output. Now
the inductor experiences a reversed voltage equal
to Vout and its current ramps down linearly. As
expressed in the Operation section under In-
ductor Over-Current Protection, a minimum
TOFF timer is activated after the over-current
comparator is triggered in the previous state.
Before Toff expires, the internal PMOS will not
turn on, and the inductor will not be recharged
even when the output voltage drops below the
regulation voltage. This reduces the maximum
load current that can be delivered by this circuit.
Since TOFF is reverse proportional to the VOUT
pin voltage, the VOUT pin is pulled up using a
voltage divider tying to the input voltage. As a
result, a 5V to 12V conversion can provide
maximum 120mA load. This buck-boost circuit
can regulate an output voltage higher, lower or
equal to the input voltage.
VIN 4.5-6.5 VDC
R1 RVIN RB
11.3k 5.0 100k
R2
4.02k
CVIN
1.0µF
CIN
47µF
1 PVIN
®
LX 10
2 VIN
PGND 9
3
SP6650
BLON U1
GND
8
4 ILIM
VOUT 7
5 SHDN
FB 6
L3
47µH
D1
MBR0530TI
R2
Q1
86k
FDS637AN
R3
10k
12V/150mA
COUT1
100µF/16V
Figure 19. Additional Application Circuit: VIN = 5.0V, VOUT = 12V, and Max ILOAD = 150mA.
VIN 4.5-6.5 VDC
R1
11.3k
RVIN RB
10.0 100k
R2
4.02k
CVIN
4.7µF
CIN
47µF
1 PVIN
®
LX 10
2 VIN
PGND 9
3
SP6650
BLON U1 GND
8
4 ILIM
VOUT 7
5 SHDN
FB 6
L1
47µH
D1
MBR0530T1
Q1
FDS637AN
R2
30.9k
Cf2
470pF
R3
10.2k
5V/250mA
COUT1
47µF
COUT2
47µF
Figure 20. Additional Application Circuit: VIN= 5.0V, VOUT = 5.0V, ILOAD = 250mA.
Date: 5/25/04
SP6650 High Efficiency 600mA Synchronous Buck Regulator
14
© Copyright 2004 Sipex Corporation
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