RT8800A Ver la hoja de datos (PDF) - Richtek Technology
Número de pieza
componentes Descripción
fabricante
RT8800A Datasheet PDF : 21 Pages
| |||
COMP VRAMP_Valley
Cross-over
SS_Internal
VCORE
SSE_Internal
S/H CKT
+
T1
-
IX
T3
RT8800A
LX
RLX
ILX
RX
CX
+ VX -
VOUT
Figure 2
Time-Sharing DCR Current Sensing
RT8800A adopts an innovative time-sharing DCR current
sensing technique to sense the phase currents for phase
current balance (phase thermal balance), over current
protection and load line regulation as shown in Figure 3.
The current sensing amplifier GM samples and holds
voltages VX across the current sensing capacitor CX by
turns in a switching cycle. According to the Basic Circuit
Theory, if
L X = R X × CX then VX = ILX ×RLX
RLX
Consequently, the sensing current IX is proportional to
inductor current ILX and is expressed as
IX = ILX ×RLX
RCOMM
The sensed current IX is used for current balance, over
current protection, and droop tuning as described as
followed. Since all phases share one common GM, GM
offset and linearity variation effect are eliminated in
practical applications. As sub-milli-ohmgrade inductors are
widely used in modern motherboards, slight mismatch of
GM amplifiers offset and linearity results in considerable
current shift between phases. The time sharing DCR current
sensing technical is extremely important to guarantee
phase current balance at mass production.
T2
Figure 3
RCOMM
Figure 4 and 5 show the linearity of GM amplifier and its
test circuit respectively. A voltage source is applied to
ISPx while other ISPx pins are short to VOUT. The voltage
VADJ across resistor RADJ is measured. It is observed from
Figure 5 shows that all ISPx share the same
transconductance linearity and voltage offset.
GM
70
60
GM3
50
GM2
40
30
20
GM1
10
0
0
20
40
60
80
100
VXC (mV)
Figure 4. The Linearity of GMx
All brand name or trademark belong to their owner respectively
DS8800A-04 August 2007
www.richtek.com
11
Share Link: 