LV5768M Ver la hoja de datos (PDF) - SANYO -> Panasonic
Número de pieza
componentes Descripción
Fabricante
LV5768M Datasheet PDF : 15 Pages
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LV5768M
6) Phase compensation set
Since LV5768M adopts current mode control, low ESR capacitor and solid polymer capacitor such as OS capacitor
can be used as output capacitor with simple phase compensation.
*Frequency characteristics
Frequency characteristics of LV5768M consist of the following transfer functions.
(1) Output resistor bleeder
(2) Voltage gain of error amplifier
Current gain (Trans conductance)
(3) Impedance of external phase compensation part
(4) Current sense loop gain
(5) Output smoothing impedance
; HR
; GVEA
; GMEA
; ZC
; GCS
; ZO
SLOPE
OSC
ΔVI
VREF
FB
GVER
- GMER
+
Error
amplifier
CLK
ΔVO
PWM
comparator
-
+
COMP
CC
RC
1/GCS
Current
sense loop
SW
VIN
L
VO
CO RL
R2
R1
HR
Fig. Current control loop of LV5768M
Closed loop gain is obtained by the equation (5)
G = HR × GMEA × ZC × GCS × ZO
R5
=
VREF
VO
× GMER ×
(RC
+
1
SCC
)
×
GCS
×
RL
1+ SCORL
(4)
From the equation (4), the frequency characteristics of closed loop gain is given by pole fp1 which consists of output
capacitor Co and output load resistor RL, zero point fz which is given by external resistor Rc and capacitor Cc of
phase compensation pin COMP and pole fp2 which is given by output impedance ZO and external phase
compensation capacitor Cc of error amplifier. fp1, fz, fp2 are given by the equation (5), (6) and (7).
fp1 =
1
2πCORL
(5), fz =
1
2πCCRL
(6),
fp2
=
2π
×
1
ZEA
×
CC
(7)
*Calculation of phase compensation external constants RC and CC
In general, the frequency where closed loop gain becomes 1 (zero cross frequency fzc) should be 1/10 of the
switching frequency (or 1/5 at the highest) to stabilize the operation of switching regulator.
Ex) When switching frequency of LV5768M is 100kHz:
fzc =
100kHz
10
≈
10kHz
(8)
Since the closed loop gain becomes 1 with this frequency, the equation (7) = 1
Vref
VO
×
GMEA
×
(RC
+
1
SCC
)
×
GCS1+SRCLORL
=1
(9)
1
In reality for zero cross frequency, in the impedance of phase compensation capacity, since capacity element SCC
1
becomes lower enough than the resistor element RC: RC » SCC
(10)
PS No.A1988-10/15
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