Application Notes: continued
V
IN
Pole due to error amplifier
output impedance and C
1
A
f
z
= 1/2pR C
4 1
V
V
OUT
V
OUT
= 18V, Select > 2V
= 16V, Select < 0.8V
ENABLE
IN
f
P
= 1/pR C
4 2
NC
NC
V
REG
+G
C
L=33mH
5V
G
V
LIN
B
100mF
ESR<8W
error amplifier gain
-20dB/dec
V
I
SW
BIAS
C
88mF
OUT
R
BIAS
= 64.9kW
(2)
Gnd
Gnd
Gnd
Gnd
f
P
= 1/p R
C
Load OUT
R
1
100kW
Gnd
Gnd
Gnd
Gnd
f
CO
MICROPROCESSOR
0
V
V
RESET
FB1
FB2
R
(1)
946W
7.5kW
2
C
Delay
WDI
C
0.1mF
modulator gain + feedback resistor divider attenuation
delay
R
3
SELECT
COMP
-G
C
OSC
C
COMP
C
OSC
390pF
0.33mF
f
= 1/2p ESR C
OUT
z
Figure 10. Bode plot of error amplifier (OTA) gain and modulator gain
added to the feedback resistor divider attenuation.
Figure 11. A typical application diagram with external components con-
figured in a boost topology.
A pole at point C:
Step 9
fp = 1/(¹R4C2),
(8g)
Finally the watchdog timer period and Power on Reset
time is determined by:
offsets the zero set by the ESR of the output capacitors.
An alternative scheme uses a single capacitor as shown in
Figure 11, to roll the gain off at a relatively low frequency.
tDelay = 1.353 ´ CDelayRBIAS
.
(9)
Linear Regulator Output Current vs. Input Voltage
100
100
75
50
25
0
75
50
25
0
Q
= 35°C/W
JA
Q
= 55°C/W
JA
V
= 14V
IN
V
= 14V
IN
Max Total Power = 1.86W
Max Total Power = 1.18W
15
30
15
30
0
5
10
20
25
0
5
10
20
25
V
(V)
V
(V)
REG
REG
Figure 12: The shaded area shows the safe operating area of the CS5112 as a function of ILIN, VREG, and QJA. Refer to the table below for typical
loads and voltages.
Worst Case Switcher
Power Available
(QJA = 55¡C/W)
Worst Case Switcher
Power Available
(QJA = 35¡C/W)
Linear Power
Dissipation
VREG
(V)
20
20
20
20
25
25
25
25
VIN
(V)
14
14
14
14
14
14
14
14
ILIN
(mA)
25
50
75
100
25
50
75
100
(W)
(W)
0.74
0.35
*
(W)
1.42
1.03
0.64
0.26
1.26
0.75
0.24
*
0.44
0.83
1.22
1.60
0.60
1.11
1.62
2.14
*
0.58
0.07
*
*
* Subjecting the CS5112 to these conditions will exceed the maximum total power that the part can handle, thereby forcing it into thermal limit.
9
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
