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參數(shù)資料
| 型號： | AN32502A |
| 英文描述： | For Information·Communication - PDA |
| 中文描述： | 信息·通訊-掌上電腦 |
| 文件頁數(shù)： | 39/45頁 |
| 文件大小： | 574K |
| 代理商： | AN32502A |
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39
SDF00034AEB
AN32502A
Publication data: November 2002
Ch.4 is a step-down DC-DC converter of synchronous rectifying type.
Figure 6
7 shows internal block configuration of ch.4.
Output voltage is determined by the following equation.
Vout
=
V
REF
is 1.07 V initially.
When high precision is required for output voltage, use a high precision resistor for R41 and R42, respectively.
R41 and R42 are influenced not by absolute precision, but by relative precision. Therefore, when using a resistor of
±
0.5%
precision resistor, output voltage varies for maximum
±
1%.
1) PWM comparison block
PWM comparator controls the on period of output pulse depending on input voltage.
Set output voltage to “High” and power on N-channel output MOS while triangular wave oscillation voltage is lower than pin 13
(SS4) and pin 14 (error amplifier output) voltages.
This circuit is able to operation up to maximum duty of 100%.
Insertion of a capacitor between pin 13 and GND allows for a soft start operation of gradually widening on period of output
pulse at startup time so that overshoot and undershoot at startup time.
The constant at the time of soft start is determined by the internal R401 and the external capacitor of pin 13.
C41 and R44 are the additional components to improve transient response characteristics coming up when load current is
suddenly changed.
On the condition of this test board, the control output voltage on sudden load change of 0 mA to 500 mA
(changing time 10
μ
sec)
Can be controlled approximately to 90 mV.
15
13
14
18
17
16
19
VB1
VB5
4K
166K
VREFH
1.95V
SSWC
V
1.07V
OSC
CTL
6
VB5
HC4
LC4
PGND4
S
I
F
S
R43
R41
R42
R44
C41
C42
D
C
C
Q41
Q42
L4
R401
R402
+
-
R42
R41
+
R42
×
V
REF
Application Notes (continued)
6
.
Explanation of operation (continued)
Ch.4
Figure 6
7
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