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参数资料
| 型号： | GM3255S8R |
| 厂商： | American Power Management Inc. |
| 元件分类： | DC/DC变换器 |
| 英文描述： | 1.5A 280kHz DC-DC CONVERTOR BOOST REGULATOR |
| 中文描述： | 1.5A的为280kHz的DC - DC转换器升压稳压器 |
| 文件页数： | 4/19页 |
| 文件大小： | 234K |
| 代理商： | GM3255S8R |
Where:
In selecting appropriate values for the slope compen-
sation network, the designer is advised to choose a
convenient capacitor, then select values for R2 and R3
such that the amount of slope compensation added is
100mA /s. Then R2 may increased or decreased as
necessary. Of course, the series combination of R2
and R3 should be large enough to avoid drawing ex-
cessive current from V
. Additionally, to ensure that
SW
the control loop stability is improved, the time constant
formed by the additional components should be cho-
sen such that
Finally, it is worth mentioning that the added slope
compensation is a trade-off between duty cycle stability
and transient response. The more slope compensation
a designer adds, the slower the transient response will
be, due to the external circuitry interfering with the
proper operation of the error amplifier.
Soft Start
Through the addition of an external circuit, a soft-start
function can be added to GM3255 of components.
Soft-start circuitry prevents the V
pin from slamming
C
high during startup, thereby inhibiting the inductor cur-
rent from rising at a high slope.
This circuit, shown in Figure 15, requires a minimum
number of components and allows the soft-start cir-
cuitry to activate any time the SS pin is used to restart
the converter.
DI /DT = the amount of slope compensation added (A/s);
V
= the voltage at the switch node when the transistor
SW
is turned off (V);
f
= the switching frequency, typically 280kHz
SW
(GM3255) or 560kHz
D = the duty cycle;
R = 0.063W, the value of the internal emitter resistor;
E
A = 5V/V, the gain of the current sense amplifier.
V
RC <
33
1 - D
f
SW
Resistor R1 and capacitors C1 and C2 form the com-
pensation network. At turn on, the voltage at the VC
pin starts to come up, charging capacitor C3 through
Schottky diode D2, clamping the voltage at the V pin
C
such that switching begins when V
reaches the V
CC
threshold, typically 1.05V (refer to graphs for detail
over temperature).
Therefore, C3 slows the startup of the circuit by limit-
ing the voltage on the V
pin. The soft- start time in-
C
creases with the size of C3.
Diode D1 discharges C3 when SS is low. If the shut-
down function is not used with this part, the cathode of
D1 should be connected to V .
IN
Calculating Junction Temperature
To ensure safe operation of the GM3255, the de-
signer must calculate the on-chip power dissipation
and determine its expected junction temperature.
Internal thermal protection circuitry will turn the part off
once the junction temperature exceeds 180°C ± 30°C.
However, repeated operation at such high tempera-
tures will ensure a reduced operating life.
Calculation of the junction temperature is an impre-
cise but simple task. First, the power losses must be
quantified. There are three major sources of power
loss on GM3255:
Biasing of internal control circuitry, PBIAS
Switch driver, PDRIVER
Switch saturation, PSAT
The internal control circuitry, including the oscillator
and linear regulator, requires a small amount of power
even when the switch is turned off. The specifications
section of this datasheet reveals that the typical oper-
ating current I , due to this circuitry is 5.5 mA.
Q
Additional guidance can be found in the graph of op-
erating current vs. temperature. This graph shows that
I
is strongly dependent on input voltage, V , and
QIN
temperature. Then
Since the onboard switch is an NPN transistor, the
base drive current must be factored in as well. This
current is drawn from the V
pin, in addition to the
IN
control circuitry current. The base drive current is
listed in the specifications as DI/DI
or switch
,
CC
SW
transconductance. As before the designer will find ad-
ditional guidance in the graphs. With that information,
the designer can calculate
V = V
+ V
C
F(D2)
C3
Figure 15. Soft Start
V
IN
SS
Test
C3
D1
V
CC
4 A
V
C
C1
R1
C2
Q
SS
Test
P
= V I
BIAS
IN Q
P
= V I
X
XD
DRIVER
IN SW
ICC
DISW
G
M
3
2
5
12
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相关代理商/技术参数 |
参数描述 |
|---|---|
| GM3255S8T | 制造商:GAMMA 制造商全称:GAMMA 功能描述:1.5A 280kHz DC-DC CONVERTOR BOOST REGULATOR |
| GM330K | 制造商:Mallory Sonalert Products Inc 功能描述:Cap Ceramic 33pF 500V SL 10% (6 X 4mm) Radial 6.4mm 85°C 制造商:CORNELL DUBILIER ELECTRONICS 功能描述:Cap Ceramic 33pF 500V SL 10% (6 X 4mm) Radial 6.4mm 85°C |
| GM331K | 功能描述:瓷片电容器 500V 330pF DISC RoHS:否 制造商:Vishay/Cera-Mite 电容:0.01 uF 容差:20 % 电压额定值:3 kV 工作温度范围:- 25 C to + 105 C 损耗因数 DF: 端接类型:Radial 产品:High Voltage Ceramic Disc Capacitors |
| GM3326 | 制造商:GAMMA 制造商全称:GAMMA 功能描述:PWM,PWM/PFM SWITCHING STEP-UP & DOWN DC/DC CONVERTER CONTROLLER ICS |
| GM3326-2.5ST25R | 制造商:GAMMA 制造商全称:GAMMA 功能描述:PWM,PWM/PFM SWITCHING STEP-UP & DOWN DC/DC CONVERTER CONTROLLER ICS |
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