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参数资料
| 型号： | MAX1876EEG+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 16/21页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 24-QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 660kHz |
| 占空比： | 90% |
| 电源电压： | 4.75 V ~ 23 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 24-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
Dual 180° Out-of-Phase PWM Step-
Down Controllers with POR
GAIN = +V IN /V RAMP FOR
FREQUENCIES LOWER
P
DH
N
THAN NYQUIST
W
L
V OUT
L
COMP_
V C
g M_GROUP
M
DL
FB
N
LX
R ESR
C OUT
=
COMP_
g M_GROUP
FB
LX
R ESR
C OUT
R COMP_
C COMP_A
C COMP_B
V SET
R COMP_
C COMP_A
C COMP_B
V SET
Figure 7. Fixed-Frequency Voltage-Mode Control Loop
× SET
A final pole is added using C COMP_B to reduce the
gain and attenuate noise after crossover. This pole
(f COMP_B ) occurs at:
f CO = GBW =
V IN
V RAMP
V
V OUT
f COMP _ B =
1
2 π × R COMP C COMP _ B
×
g M _ COMP × R COMP × R ESR
2 π × L
2 × LC OUT
Figure 8 shows a Bode plot of the poles and zeros in
their relative locations.
Near crossover the following approximations can be
made to simplify the loop-gain equation:
? R COMP has much higher impedance than C COMP .
This is true if, and only if, crossover occurs above
f Z_COMP_A . If this is true, C COMP_A can be ignored
(as a short to ground).
? R ESR is much higher impedance than C OUT . This is
true if, and only if, crossover occurs well after the out-
put capacitor ’ s ESR zero. If this is true, C OUT
becomes an insignificant part of the loop gain and can
be ignored (as a short to ground).
? C COMP_B is much higher impedance than R COMP
To ensure stability, select R COMP to meet the following
criteria:
? Unity-gain crossover must occur below 1/5th of the
switching frequency.
? For reasonable phase margin using type 1 compen-
sation, f CO must be larger than 5 ? f ESR .
Choose C COMP_A so that f Z_COMP_A equals half f LC
using the following equation:
C COMP _ A =
R COMP
Choose C COMP_B so that f COMP_B occur at 3 times f CO
using the following equation:
( )
and can be ignored (as an open circuit). This is true
if, and only if, crossover occurs far below f COMP_B .
The following loop gain equation can be found by using
these previous approximations with Figure 7:
C COMP _ B =
1
2 π × 3 × f CO × R COMP
MOSFET Selection
× ×
A L ?
V IN
V RAMP
V SET
V OUT
g M _ COMP × R COMP × R ESR
sL
The MAX1875/MAX1876s ’ step-down controller drives
two external logic-level N-channel MOSFETs as the cir-
cuit switch elements. The key selection parameters are:
Setting the loop gain to 1 and solving for the crossover
frequency yields:
? On-resistance (R DS(ON) )
? Maximum drain-to-source voltage (V DS(MAX) )
16
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