參數(shù)資料
型號: LTC1704B
廠商: Linear Technology Corporation
元件分類: 通用總線功能
英文描述: Synchronous 8-Bit Up/Down Binary Counters 24-SOIC 0 to 70
中文描述: 550kHz的同步開關(guān)穩(wěn)壓器控制器加線性穩(wěn)壓控制器
文件頁數(shù): 24/28頁
文件大?。?/td> 343K
代理商: LTC1704B
LTC1704/LTC1704B
24
1704bfa
APPLICATIU
W
U
U
doesn’t cause a bigger spike than the transient signal
being measured. Conveniently, the typical probe tip ground
clip is spaced just right to span the leads of a typical output
capacitor. Make sure the bandwidth limit on the scope is
turned off, since a significant portion of the transient
energy occurs above the 20MHz cutoff.
Now that we know how to measure the signal, we need to
have something to measure. The ideal situation is to use
the actual load for the test, and switch it on and off while
watching the output. If this isn’t convenient, a current step
generator is needed. This generator needs to be able to
turn on and off in nanoseconds to simulate a typical
switching logic load, so stray inductance and long clip
leads between the LTC1704 and the transient generator
must be minimized.
Figure 12 shows an example of a simple transient genera-
tor. Be sure to use a noninductive resistor as the load
element—many power resistors use an inductive spiral
pattern and are not suitable for use here. A simple solution
is to take ten 1/4W film resistors and wire them in parallel
to get the desired value. This gives a noninductive resistive
load which can dissipate 2.5W continuously or 50W if
pulsed with a 5% duty cycle, enough for most LTC1704
circuits. Solder the MOSFET and the resistor(s) as close to
the output of the LTC1704 circuit as possible and set up
the signal generator to pulse at a 100Hz rate with a 5% duty
cycle. This pulses the LTC1704 with 500
μ
s transients
10ms apart, adequate for viewing the entire transient
recovery time for both positive and negative transitions
while keeping the load resistor cool.
LINEAR REGULATOR SUPPLY
Linear Regulator Output Voltage
The linear regulator senses the output voltage at V
OUTREG
with an internal amplifier (see Figure 13). The amplifier
negative input is connected internally to an 800mV refer-
ence, while the positive input is connected to the REGFB
pin. The amplifier output drives a P-channel transistor
MREG, which is in turn connected to the external NPN pass
transistor. The linear regulator output voltage can be
obtained using the following equation:
V
V
R
R
OUTREG
=
+
0 8
.
1
5
6
Figure 12. Transient Load Generator
LTC1704
V
OUTSW
IRFZ44 OR
EQUIVALENT
R
LOAD
50
0V TO 10V
100Hz, 5%
DUTY CYCLE
LOCATE CLOSE TO THE OUTPUT
1704 F12
PULSE
GENERATOR
Figure 13. Linear Regulator
QEXT
MOFF
R5
R6
REGDR
REGILM
MREG
V
CC
V
REF
2mA
REGFB
1704 F13
+
C
OUTREG
V
OUTREG
V
REGON
R
REGILM
C
DELAY
I
P
V
INREG
REGOFF
V
CC
1.9
μ
A
LTC1704
REG
ILM
+
REGFB
+
AMP
Linear Regulator Supplies Requirement
The linear regulator operates with two supplies: V
CC
for the
LTC1704 and V
INREG
for the external NPN transistor QEXT.
Both supplies must be higher than the minimum value
determined by the linear regulator output voltage, V
OUTREG
.
For a desired V
OUTREG
, use the following formula to
calculate the minimum required V
CC
:
Minimum V
CC
= V
OUTREG
+ V
BE(QEXT)
+ V
DROPOUT
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