RT8802A
OCP Comparator
EA Rising Slew Rate
1/3 I
+
-
X
1/2 I
IMAX
VFB
Figure 16. Over Current Comparator
Phase current OCP and total current OCP with
thermal compensation
V-comparator
∝
I
I
L(n)
X(n)
I 1
X
+
I
I
I
I
, Phase
-
OC
OC
OC
OC
V-comparator
CH1:(500mV/Div)
CH2:(2V/Div)
VCOMP
I 2
X
, Phase
+
-
H Pulse width detector
H Last 20us? Y = 1, N = 0
V-comparator
Short circuit
protection
I 3
X
, Phase
+
Time (250ns/Div)
-
OCP
V-comparator
Figure 19. EA Falling Transient with 10pF Loading ;
I 4
X
, Phase
+
-
Slew Rate = 8V/μs
Over current
protection
H Pulse width detector
H Last 20us? Y = 1, N = 0
Thermal compensated OCP
Reset while VID changing
4.7k
4.7k
B
Figure 17
Error Amplifier Characteristic
-
A
EA
+
V
REF
For fast response of converter to meet stringent output
current transient response, RT8802Aprovides large slew
rate capability and high gain-bandwidth performance.
Figure 20. Gain-Bandwidth Measurement by signalA
divided by signal B
EA Falling Slew Rate
Design Procedure Suggestion
a. Output filter pole and zero (Inductor, output capacitor
value & ESR).
VFB
b. Error amplifier compensation & saw-tooth wave
amplitude (compensation network).
c. Kelvin sense for VCORE
.
Current Loop Setting
CH1:(500mV/Div)
CH2:(2V/Div)
VCOMP
a. GM amplifier S/H current (current sense component
DCR, ISPX and ISNX pin external resistor value).
Time (250ns/Div)
b. Over current protection trip point (RIMAX resistor).
Figure 18. EA Rising Transient with 10pF Loading ;
Slew Rate = 10V/μs
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
All brandname or trademark belong to their owner respectively.
DS8802A-09 March 2012
www.richtek.com
27
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
