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参数资料
| 型号： | MAX1545ETL+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 25/43页 |
| 文件大小： | 0K |
| 描述： | IC QUICK-PWM DUAL-PHASE 40-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 系列： | Quick-PWM™ |
| 应用： | 控制器，Intel Pentium? IV |
| 输入电压： | 2 V ~ 28 V |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 1.85 V |
| 工作温度： | -40°C ~ 100°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 40-WFQFN 裸露焊盘 |
| 供应商设备封装： | 40-TQFN-EP（6x6） |
| 包装： | 带卷 (TR) |
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Dual-Phase, Quick-PWM Controllers for
Programmable CPU Core Power Supplies
with input voltage feed forward (Figure 5). This archi-
tecture relies on the output filter capacitor’s ESR to act
Table 6. Approximate K-Factor Errors
as the current-sense resistor, so the output ripple volt-
age provides the PWM ramp signal. The control algo-
rithm is simple: the high-side switch on-time is
determined solely by a one-shot whose period is
inversely proportional to the input voltage, and directly
proportional to the output voltage or the difference
between the main and secondary inductor currents
(see the On-Time One-Shot (TON) section). Another
one-shot sets a minimum off-time. The on-time one-shot
triggers when the error comparator goes low, the induc-
TON
CONNECTION
V CC
Float
REF
GND
FREQUENCY
SETTING
(kHz)
100
200
300
550
K-FACTOR
(μs)
10
5
3.3
1.8
MAX
K-FACTOR
ERROR
(%)
±10
±10
±10
±12.5
t ON ( 2 ND ) = K ? CCI
?
?
?
= K ? FB
? + K ?
?
?
?
?
?
tor current of the selected phase is below the valley current-
limit threshold, and the minimum off-time one-shot times out.
The controller maintains 180° out-of-phase operation by
alternately triggering the main and secondary phases after
the error comparator drops below the output voltage set
point.
On-Time One-Shot (TON)
The core of each phase contains a fast, low-jitter,
adjustable one-shot that sets the high-side MOSFETs
on-time. The one-shot for the main phase varies the on-
time in response to the input and feedback voltages.
The main high-side switch on-time is inversely propor-
tional to the input voltage as measured by the V+ input,
and proportional to the feedback voltage (V FB ):
t ON ( MAIN ) = K ( V FB + 0 . 075 V )
V IN
where K is set by the TON pin-strap connection (Table 6)
and 0.075V is an approximation to accommodate the
expected drop across the low-side MOSFET switch.
The one-shot for the secondary phase varies the on-time
in response to the input voltage and the difference
between the main and secondary inductor currents. Two
identical transconductance amplifiers integrate the differ-
ence between the master and slave current-sense sig-
nals. The summed output is internally connected to CCI,
allowing adjustment of the integration time constant with a
compensation network connected between CCI and FB.
The resulting compensation current and voltage are
determined by the following equations:
where Z CCI is the impedance at the CCI output. The
secondary on-time one-shot uses this integrated signal
(V CCI ) to set the secondary high-side MOSFETs on-time.
When the main and secondary current-sense signals
(V CM = V CMP - V CMN and V CS = V CSP - V CSM ) become
unbalanced, the transconductance amplifiers adjust the
secondary on-time, which increases or decreases the
secondary inductor current until the current-sense
signals are properly balanced:
? V + 0 . 075 V ?
V IN
? V + 0 . 075 V ? ? I CCI Z CCI ?
V IN V IN
= ( Main On ? Time ) +
( Secondary Current Balance Correction )
This algorithm results in a nearly constant switching
frequency and balanced inductor currents, despite the
lack of a fixed-frequency clock generator. The benefits of
a constant switching frequency are twofold: first, the
frequency can be selected to avoid noise-sensitive
regions such as the 455kHz IF band; second, the induc-
tor ripple-current operating point remains relatively con-
stant, resulting in easy design methodology and
predictable output voltage ripple. The on-time one-shots
have good accuracy at the operating points specified in
the Electrical Characteristics . On-times at operating
points far removed from the conditions specified in the
Electrical Characteristics can vary over a wider range. For
I CCI = G M
( V CMP - V CMN ) - G M ( V CSP - V CSN )
V CCI = V FB + I CCI Z CCI
example, the 300kHz setting typically runs about 3%
slower with inputs much greater than 12V due to the very
short on-times required.
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