参数资料
型号: ISL6537ACR
厂商: Intersil
文件页数: 13/16页
文件大小: 0K
描述: IC REG/CTRLR ACPI DUAL DDR 28QFN
标准包装: 50
应用: 存储器,DDR/DDR2 稳压器
电流 - 电源: 7mA
工作温度: 0°C ~ 70°C
安装类型: 表面贴装
封装/外壳: 28-VQFN 裸露焊盘
供应商设备封装: 28-QFN(6x6)
包装: 管件
ISL6537A
The modulator transfer function is the small-signal transfer
function of V OUT /V E/A . This function is dominated by a DC
100
F Z1 F Z2
F P1
F P2
Gain and the output filter (L O and C O ), with a double pole
80
break frequency at F LC and a zero at F ESR . The DC Gain of
the modulator is simply the input voltage (V IN ) divided by the
peak-to-peak oscillator voltage Δ V OSC .
Modulator Break Frequency Equations
60
40
20
20LOG
(R 2 /R 1 )
OPEN LOOP
ERROR AMP GAIN
20LOG
F LC = -------------------------------------------
F ESR = -------------------------------------------- (EQ. 4)
F LC
1 1
2 π x LO x CO 2 π x ESR x C O
The compensation network consists of the error amplifier
(internal to the ISL6537A) and the impedance networks Z IN
and Z FB . The goal of the compensation network is to provide
a closed loop transfer function with the highest 0dB crossing
frequency (f 0dB ) and adequate phase margin. Phase margin
0
-20
-40
-60
10
MODULATOR
GAIN
100
1K
(V IN / Δ V OSC )
F ESR
10K 100K 1M
FREQUENCY (Hz)
COMPENSATION
GAIN
CLOSED LOOP
GAIN
10M
is the difference between the closed loop phase at f 0dB and
180 degrees. The equations below relate the compensation
network’s poles, zeros and gain to the components (R 1 , R 2 ,
R 3 , C 1 , C 2 , and C 3 ) in Figure 3. Use these guidelines for
locating the poles and zeros of the compensation network:
FIGURE 4. ASYMPTOTIC BODE PLOT OF CONVERTER GAIN
Output Voltage Selection
The output voltage of all the external voltage regulators can
1.
2.
3.
4.
5.
6.
7.
Pick Gain (R 2 /R 1 ) for desired converter bandwidth.
Place 1 ST Zero Below Filter’s Double Pole (~75% F LC ).
Place 2 ND Zero at Filter ’s Double Pole.
Place 1 ST Pole at the ESR Zero.
Place 2 ND Pole at Half the Switching Frequency.
Check Gain against Error Amplifier ’s Open-Loop Gain.
Estimate Phase Margin - Repeat if Necessary.
be programmed to any level between their individual input
voltage and the internal reference, 0.8V. An external resistor
divider is used to scale the output voltage relative to the
reference voltage and feed it back to the inverting input of the
error amplifier, refer to the Typical Application on page 4.
The output voltage programming resistor will depend on the
value chosen for the feedback resistor and the desired
Compensation Break Frequency Equations
output voltage of the particular regulator.
F Z1 = ------------------------------------
F P1 = ---------------------------------------------------------
2 π x R 2 x ? ---------------------- ?
R1 × 0.8V
1
2 π x R 2 x C 1
1
? C 1 x C 2 ?
? C 1 + C 2 ?
R4 = -----------------------------------
V DDQ – 0.8V
F Z2 = -------------------------------------------------------
F P2 = ------------------------------------
R5 × 0.8V
1
2 π x ( R 1 + R 3 ) x C 3
1
2 π x R 3 x C 3
(EQ. 5)
R8 = ----------------------------------------
V GMCH – 0.8V
R9 × 0.8V
R11 × 0.8V
Figure 4 shows an asymptotic plot of the DC/DC converter’s
gain vs. frequency. The actual Modulator Gain has a high gain
peak due to the high Q factor of the output filter and is not
shown in Figure 4. Using the above guidelines should give a
Compensation Gain similar to the curve plotted. The open
loop error amplifier gain bounds the compensation gain.
Check the compensation gain at F P2 with the capabilities of
R10 = -----------------------------------------------------------
xxxxxxxxxxxx
V TT_GMCH/CPU – 0.8V
R12 = ----------------------------------
V DAC – 0.8V
(EQ. 6)
the error amplifier. The Closed Loop Gain is constructed on
the graph of Figure 4 by adding the Modulator Gain (in dB) to
the Compensation Gain (in dB). This is equivalent to
multiplying the modulator transfer function to the
compensation transfer function and plotting the gain.
The compensation gain uses external impedance networks
Z FB and Z IN to provide a stable, high bandwidth (BW) overall
loop. A stable control loop has a gain crossing with
-20dB/decade slope and a phase margin greater than 45
degrees. Include worst case component variations when
determining phase margin.
13
If the output voltage desired is 0.8V, simply route the output
voltage back to the respective FB pin through the feedback
resistor and do not populate the output voltage programming
resistor.
The output voltage for the internal V TT_DDR linear regulator
is set internal to the ISL6537A to track the V DDQ voltage by
50%. There is no need for external programming resistors.
FN9143.5
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