参数资料
型号: ISL6526AEVAL1
厂商: Intersil
文件页数: 10/15页
文件大小: 0K
描述: EVALUATION BOARD 1 ISL6526A
标准包装: 1
主要目的: DC/DC,步降
输出及类型: 1,非隔离
输出电压: 2.5V
电流 - 输出: 5A
输入电压: 3.3 ~ 5 V
稳压器拓扑结构: 降压
频率 - 开关: 600kHz
板类型: 完全填充
已供物品:
已用 IC / 零件: ISL6526A
ISL6526, ISL6526A
the PHASE node. The PWM wave is smoothed by the output
filter (L O and C O ).
The modulator transfer function is the small-signal transfer
function of V OUT /V E/A . This function is dominated by a DC
Gain and the output filter (L O and C O ), with a double pole
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 .
2. Place first zero below filter’s double pole (~75% f LC ).
3. Place second zero at filter ’s double pole.
4. Place first pole at the ESR zero.
5. Place second pole at half the switching frequency.
6. Check gain against error amplifier ’s open-loop gain.
7. Estimate phase margin - repeat if necessary.
Compensation Break Frequency Equations
f Z1 = ----------------------------------
OSC
DRIVER
V IN
1
2 π × R 2 × C 2
(EQ. 6)
f Z2 = -------------------------------------------------------
f P1 = ---------------------------------------------------------
2 π x R 2 x ? ?
? C 1 x C 2 ?
f P2 = ------------------------------------
Δ V OSC
PWM
COMPARATOR
-
+
Z FB
V E/A
-
+
DRIVER
Z IN
L O
PHASE
C O
ESR
(PARASITIC)
V OUT
1
2 π x ( R 1 + R 3 ) x C 3
1
----------------------
? C 1 + C 2 ?
1
2 π x R 3 x C 3
(EQ. 7)
(EQ. 8)
(EQ. 9)
ERROR
AMP
REFERENCE
Figure 6 shows an asymptotic plot of the DC/DC converter’s
DETAILED COMPENSATION COMPONENTS
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
C 2
C 1
R 2
Z FB
C 3
Z IN
R 3
V OUT
shown in Figure 6. Using the previously mentioned 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
COMP
-
FB
R 1
of the error amplifier. The Closed Loop Gain is constructed on
the graph of Figure 6 by adding the Modulator Gain (in dB) to
the Compensation Gain (in dB). This is equivalent to
+
ISL6526, ISL6526A
REFERENCE
FIGURE 5. VOLTAGE-MODE BUCK CONVERTER
COMPENSATION DESIGN
Modulator Break Frequency Equations
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°. Include worst case component variations when
f LC = ------------------------------------------
f ESR = -------------------------------------------
? V IN ?
1
2 π x L O x C O
1
2 π x ESR x C O
(EQ. 4)
(EQ. 5)
determining phase margin.
f Z1 f Z2
100
80
60
f P1
f P2
OPEN LOOP
ERROR AMP GAIN
20 log ? ------------------ ?
? V OSC ?
The compensation network consists of the error amplifier
20 log ? -------- ?
(internal to the ISL6526, ISL6526A) 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 is the difference between the closed
40
20
0
-20
R2
? R1 ?
COMPENSATION
GAIN
loop phase at f 0dB and 180°. Equations 6, 7, 8 and 9 relate
the compensation network’s poles, zeros and gain to the
-40
MODULATOR
GAIN
f LC
f ESR
LOOP GAIN
components (R 1 , R 2 , R 3 , C 1 , C 2 , and C 3 ) in Figure 5. Use
these guidelines for locating the poles and zeros of the
compensation network:
1. Pick gain (R 2 /R 1 ) for desired converter bandwidth.
10
-60
10 100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
FIGURE 6. ASYMPTOTIC BODE PLOT OF CONVERTER GAIN
FN9055.10
November 24, 2008
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