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參數(shù)資料
| 型號： | MB3785A |
| 廠商： | Fujitsu Limited |
| 英文描述： | Switching Regulator Controller (4 Channels plus High-Precision, High-Frequency Capabilities) |
| 中文描述： | 開關穩(wěn)壓器控制器（4通道加高精度，高頻率功能） |
| 文件頁數(shù)： | 17/29頁 |
| 文件大?。?/td> | 293K |
| 代理商： | MB3785A |
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17
MB3785A
I
METHOD OF SETTING TIME CONSTANT FOR TIMER/LATCH-ACTUATED SHORT-
CIRCUTING PROTECTION CIRCUIT
Figure 5 schematically shows the protection latch circuit.
The outputs from the output-shorting detection comparators 1 to 4 are respectively connected to the inverted inputs
of the SCP comparator. These inputs are always compared with the reference voltage of approximately 2.1 V which
is fed to the non-inverted input of the SCP comparator.
While the switching regulator load conditions are stable, there are no changes in the outputs of the comparators 1
to 4 so that short-circuit protection control keeps equilibrium state. At this time, the voltage on the SCP terminal
(pin 23) is held at approximately 50 mV.
When load conditions change rapidly due to a short-circuiting of load, for example, the output voltage of the
comparator for the relevant channel goes “H” (2.1 V or more). Consequently, the SCP comparator outputs a “L”,
causing the transistor Q
1
to turn off, and the short-circuit protection capacitor C
PE
(externally fitted to the SCP
terminal) begins to charge.
V
PE
= 50 mV + t
PE
×
10
–6
/C
PE
0.65 = 50 mV + t
PE
×
10
–6
/C
PE
C
PE
= t
PE
/0.6 (sec)
When the external capacitor C
PE
is charged to approximately 0.65 V, the SR latch is set and the output drive transistor
is turned off. Simultaneously, the dead time is extended to 100% and the output voltage on the SCP terminal (pin
23) is held “L”. As a result, the S-R latch input is closed and C
PE
is discharged.
Figure 5. Protection Latch Circuit
Comparator 1
Comparator 2
Comparator 3
Comparator 4
2.1 V
Q
1
Q
2
C
PE
1
μ
A
S
R
Latch
U.V.L.O
PWM
comparator
OUT
2.5 V
23
+
–
–
–
–
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