ISL6529CR-T Intersil, ISL6529CR-T Datasheet - Page 12

• Manufacturer Part Number: ISL6529CR-T
• Description: IC CTRLR PWM DUAL REG 16-QFN
• Manufacturer: Intersil
• Type: Step-Down (Buck)r

Specifications of ISL6529CR-T

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.5 ~ 4.5 V
• Frequency - Switching: 600kHz
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-VQFN Exposed Pad, 16-HVQFN, 16-SQFN, 16-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Voltage - Input: -
• Power - Output: -

The Compensation Network
To provide for system stability with a low ESR output
capacitor, where pole cancellation by the capacitor is outside
the frequencies of interest, a phase lead network must be
used to compensate for the phase lag resulting from
MOSFET output resistance and the output capacitor.
Figure 11 shows the type II compensation network
configuration and a simplified straight line representation of
the network response. By using the equations in Figure 11,
-135
FIGURE 10. LOOP RESPONSE WITH ONLY 100µF, 5mΩ
-45
-90
FIGURE 11. SCHEMATIC AND BODE PLOT OF
BODE PLOT OF REGULATOR (N0 COMP) AT 3 OUTPUT CURRENTS
-100
-150
-200
80
60
40
20
REGULATED
80
70
60
50
40
30
20
10
0
-50
0
0
10
80
60
40
10
20
0
0
10
OUTPUT
---------------------------------- -
2π R12 C4
100
100
OUTPUT CAPACITOR
COMPENSATION NETWORK
100
INTERNAL 0.8V
⋅
REFERENCE
1
ISL6529
⋅
R5
FB
1,000
1K
1K
1mA
FREQUENCY (Hz)
55mA
FREQUENCY (Hz)
--------------------------------------------------------- -
2π R12
3A
C4
12
⋅
10K
10,000
+
-
10K
55mA
1mA
3A
C16
⋅



1
------------------------ -
C 16
C16 C4
R12
DRIVE 2
100K
+
100K
⋅
100,000
C 4



TO MOSFET
20
1M
1,000,000
1M
1mA
55mA
⋅
log
ISL6529, ISL6529A
R12
---------- -
R 5
10M
10,000,000
10M
the values of R12 and C4 can be adjusted to the frequency
where phase lead begins. The second equation shows the
upper frequency where phase advance is complete. After
capacitor C4 becomes effectively an ac short, the mid band
gain is set by the R12/R5 ratio as shown on Figure 11.
Several simulations illustrate the compensation with the
more difficult 5mΩ, 100µF output capacitor. Figure 10
previously showed the Bode plots where the phase
response comes dangerously near the oscillatory 180° state
at unity gain. A type II network applied across the error
amplifier inverting input to the output can be configured to
perform this function.
Figure 12 shows the Bode plot of only the compensation
network with the system to illustrate the phase boost in the
system. Essentially the phase lead region must be moved to
advance the phase where it is close to an oscillatory state.
Increasing the value of C4 moves the response lower, aiding
the lagging phase at low frequencies and low load current.
This operation will reduce phase compensation at higher
BODE PLOT OF COMPENSATED REGULATOR AT 3 OUTPUT CURRENTS
BODE PLOT OF REGULATOR (COMP ONLY) AT 3 OUTPUT CURRENTS
FIGURE 12. LOOP RESPONSE WITH COMPENSATION
FIGURE 13. INVERTING INPUT TO OUTPUT GAIN AND
-100
-100
-150
-200
-150
-200
-50
-50
80
80
60
40
60
40
20
20
0
0
0
0
10
10
135°
NETWORK ONLY
PHASE WITH COMPENSATION AND 100µF, 5mΩ
OUTPUT CAPACITOR
100
100
1mA
1K
1K
1mA
54mA
FREQUENCY (Hz)
FREQUENCY (Hz)
10K
10K
54mA
3A
100K
100K
COMPENSATION:
3A
COMPENSATION:
C16 = 10pF
C4 = 470pF
R16 = 200K
54mA
3A
C16 = 10pF
C4 = 470pF
R16 = 200K
1M
1M
1mA
3A
1mA
3A
April 12, 2005
1mA
FN9070.5
10M
10M