SC4510 Ver la hoja de datos (PDF) - Semtech Corporation
Número de pieza
componentes Descripción
Lista de partido
SC4510 Datasheet PDF : 16 Pages
| |||
SC4510
POWER MANAGEMENT
Application Information
COMBI-SENSE OPERATION AND CURRENT LIMIT
Effective current sensing is important for the current mode
control of power convertors. Instead of using the traditional
lossy resistive current sense scheme, a novel lossless
Combi-Sense technique is used in SC4510. This SEMTECH
proprietary technology has the advantages of
When Q1/Q3 turn OFF and Q2/Q4 turn ON, the equivalent
circuit of Fig.1 becomes the sub-circuit as shown in Fig.
2b). Where Rds2 is the channel resistance of the bottom
MOSFET. In this case, the branch {Rs,Cs} is in parallel with
{(Rds2+RL), L} and VCs=(Rds2+RL)Io.
1) lossless current sensing,
2) bigger signal-to-noise ratio, and
Vin
Rds1
3) thermal run-away prevention.
The basic structure of the Combi-Sense is shown in Fig.1.
Where RL is the equivalent resistance of the output inductor.
The added Rs and Cs form the RC branch in “parallel” with
the output inductor for inductor current sensing. This
branch works with a small signal totem pole (Q3 and Q4)
integrated in SC4510 in order to improve the signal-to-noise
ratio. The base signals Vbe3 and Vbe4 are designed to
closely follow the gate signals Vgs1 and Vgs2, respectively.
Ideally, the leading and falling edges of the Virtual Phase
Node (VPN) follow that of the Phase Node (PH) when Q1~Q4
switch in perfect synchronism.
Vin
Cin
Q1
Vgs1
PN
iL(t)
L
Rs
Q2
Vgs2
RL
Cs
vC(t)
Vo
Cout Rload
PN
Cin
iL(t) L
RL
Rs Cs
Vo
VPN
Cout Rload
vC(t)
Fig.2 a) Equivalent sub-circuit.
When averaged over a complete cycle,
VCs = [D(Rds1+RL)+(1-D)(Rds2+RL)] Io
= [D Rds1+(1-D)Rds2+RL]Io
= ReqIo.
D is the operating duty ratio. It is noted that the average
DC value in VCs is independent of the value of L, Rs and Cs.
If only the average load current information is needed (such
as in average current mode control), this current sensing
method is effective without further requirements.
Vbe3
Q3
VPN
Vbe4
Q4
Vin
Fig.1 The Basic Structure of Combi-Sense.
Cin
When Q1/Q3 turn ON and Q2/Q4 turn OFF, the equivalent
circuit of Fig.1 is shown in Fig. 2a). Where, Rds1 is the on-
resistance of the top MOSFET. The two branches, consisting
of {(Rds1+RL), L} and {Rs, CS}, are in parallel. The DC voltage
drop (Rds1+RL)Io equals VCs. In this way, the output current
is sensed from VCs when (Rds1+RL) is known.
iL(t) L
RL
PN
Rs
Cs
Rds2
VPN
vC(t)
Vo
Cout Rload
Fig.2 b) Equivalent sub-circuit.
© 2004 Semtech Corp.
12
www.semtech.com
Share Link: 