an1009

ISL6560/62 Evaluation Board
®
Application Note
April 2002
AN1009.0
Author: Hal Wittlinger
Introduction
Description
The ISL6560/62 Evaluation Board was designed to
accommodate either the ISL6560 or the ISL6562 power
supply controller ICs. CORE voltage is set by a five bit DAC
that is usually programmed by the microprocessor. For this
board, DAC codes are entered via a five position dip switch.
Power supply input voltages may be applied through three
banana posts or an ATX connector on the board. With an
ATX supply the main input voltage to the converter is 5V. The
ATX 12V supply powers the ISL6560/62, the HIP6601 gate
drivers and the transient load generator. A toggle switch is
provided on the board to enable the ATX supply.
This board was design so that a wide range of input voltages
could be used. Burndy binding posts at the lower end of the
board provide the high current connections for the output
load.
Converter input voltage via the banana connectors can
range from 5V to 12V. A separate connector supplies 12V to
the ISL6560/62, transient load generator and the gate
drivers as described above.
Figure 1 shows the Evaluation Board. Note the ATX
connector at the top of the board. The ATX power switch
SW2, is located to the right of the connector.
Just above the output connectors is a pulse generator to
provide 40A transient loading to verify response to pulse
loading of the supply. Scope probe connectors monitor the
current pulse, and output voltage.
Extra output capacitor locations are available to modify the
output capacitor configuration or type of capacitors. 22µF
ceramic capacitors accompany the bulk electrolytic
capacitors. In an application where the supply is connected
to an active load, high frequency capacitors should be
located as close as possible to the load to help reduce
undesired transient voltage changes at the load.
The ISL6560/62 is located on the left side of the board.
Immediately below the controller IC is the POWER GOOD
monitoring circuit. A dual RED-GREEN LED indicator is
green when the CORE voltage is within the defined data
sheet limits. Figure 13 shows a schematic diagram of the
POWER GOOD monitoring circuit.
ISL6560 and ISL6562
Figure 2 shows a simplified functional block diagram of these
devices, outlining the major differences between the two ICs.
VCC
REF
3V REF
WRGD
UVLO and
BIAS CIRCUITS
OSCILLATOR
X0.82
+
UV
-
X1.24
+
OVP
-
CT
PWM1
VID4
VID3
VID2
VID1
VID0
CONTROL
_
LOGIC
PWM2
+
D/A
CS+
CMP
+
E/A
-
-
CS-
FB
COMP
DAC Codes
ISL6560 - VRM 9.0
ISL6562 - VRM 8.5
GND
CS Threshold Voltage
ISL6560 - 157mV
ISL6562 - 79mV
FIGURE 2. SIMPLIFIED BLOCK DIAGRAM SHOWING
MAJOR DEVICE DIFFERENCES
FIGURE 1. EVALUATION BOARD
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Copyright © Intersil Americas Inc. 2002. All Rights Reserved
ISL6560/62 Evaluation Board
The ISL6560 has a DAC scaled for VRM9.0 codes while the
ISL6562’s DAC is set to VRM8.5 codes. The other major
difference is the Current Comparator threshold voltage.
The typical threshold voltage for the ISL6560 is 157mV while
the ISL6562 is more sensitive and has a threshold voltage of
79mV.
Figure 3 shows the Current Comparator threshold voltage
versus the COMP voltage.
3.0
ISL6562 On The Board
2
VCOMP (Volts)
2.5
6
65
0
656
L
IS
2.0
1.5
or a switch. This device should be located next the COMP
pin to reduce the possibility of external pickup by the pin.
The oscillator is disabled when the COMP voltage drops
below 0.56V for the ISL6560 and 0.64V for the ISL6562.
Minimum current for the pull down device should be 2mA.
The COMP terminal is brought out as a test point on the
Evaluation Board. A ground terminal and the 3V Reference
terminal are located near the COMP terminal on the
Evaluation Board.
ni
=
V
25
V
V/
As explained earlier the board is designed to be used with
either the ISL6560 or the ISL6562. The boards are usually
shipped with the ISL6560. Boards populated with the
ISL6562 have an additional 5mΩ resistor placed in the R15
location.
ISL
5
/V
ni =
12.
1.0
Evaluation Board Quick Start
0.5
0
0
20
40
60
120
80 100
VCS(CL) (mV)
140
160
To aid in getting the board functioning as quickly as possible,
a sheet similar to Figure 4 is included with each board. This
shows the location of all pertinent parts and test points.
FIGURE 3. CURRENT COMPARATOR THRESHOLD
VOLTAGE AS A FUNCTION OF VCOMP
Oscillator
An oscillator drives a divider that reduces the channel
frequency to one half of the oscillator. Each channel is
initiated by the oscillator and terminated by the current
comparator. A maximum duty cycle of 50% is established by
this arrangement.
12V Input for
Note: ATX Supply connected
Controller
to use ATX 5V supply for
Gate Drivers
Main Input. ATX 12V is used
and Load
for low power circuitry on board.
VID Codes Generator
Pin 1
Main Supply Input
of ISL6560/62
ATX Power Switch
3.3V or 12V
5
ATX Connector
1
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Power Good
Operation of the controller is monitored by the Power Good
circuitry which controls an open drain N-Channel MOS
transistor. When the CORE voltage is outside the 82% and
124% limits, the MOSFET pulls down an external load. Over
voltage switches both upper PWM power MOSFETs OFF
and pulls down the lower output power MOSFETs to protect
the load.
Over Current
Over current is detected by the output voltage dropping
below the under voltage limit. This results in several
occurrences. First the Current Comparator limit is reduce to
95mV from 157mV for the ISL6560 and 47mV from 79mV for
the ISL6562. This effectively folds back the current, while the
CORE voltage is now set to a lower limit of 400mV to 500mV.
Moreover, the oscillator frequency is reduce to about one
fifth of its normal operating value by reducing the oscillator
charging current to 36µA from its normal operating value of
150µA.
Scope Probe
10mV/A
Internal
Load Generator
2 Position Switch
Each Position
ON - OFF
Current for
each Position:
20A at 1.500V
C
Output to an External Load
Converter Disable
To disable the converter, the COMP terminal may be pulled
to ground with a NPN transistor, N-Channel MOS transistor
2
FIGURE 4. PERTIENT POINTS ON ISL6560/62
EVALUATION BOARD
ISL6560/62 Evaluation Board
Transient Load Generator
Efficiency
Probably one of the most interesting tests for a regulator
system is the transient load. From this single test one can
access voltage droop, loop stability and the regulator’s
response to load changes going from no load to full load and
the recovery after rapid load removal. To quickly determine
these characteristics, a pulse load generator is incorporated
on the evaluation board. A current load pulse at about 20A
per position at 1.5V output is activated with two slide
switches. A scope probe connector is provided to monitor the
current pulse and is calibrated to read 10mV/A. Figures 5, 6,
and 7 show the transient response of the Evaluation Board
with 12V input, operating with the internal load generator
which provides slightly over a 40A load step. For all scope
shots: Top trace is PWM 1 output, next is VCOMP at 1V/div.
Center trace is VCORE at 50mV/div and the lower trace is the
load current at 20A/div. DAC set to 1.500V.
Figures 8 and 9 show the efficiency of the converter with
CORE voltage at the two extremes of the DAC voltage and at
1.500V, near the middle of the range. The curves show 12V
input and 5V input. Note the improvement in efficiency as the
output voltage approaches the input voltage, with increasing
duty cycle.
Snubber Networks
Snubbers are not used in this design, but pad locations and
connections to PHASE and ground are provided by R2 - C7
for PHASE 1 and R4 - C9 for PHASE 2.
100
EFFICIENCY (%)
VIN = 12V
90
VOUT = 1.85V
VOUT = 1.50V
80
VOUT = 1.10V
70
60
50
0
5
10
15
20
25
30
35
40
LOAD CURRENT (A)
FIGURE 8. 12V INPUT EFFICIENCY AT DAC EXTREMES
100
FIGURE 5. 44A TRANSIENT CURRENT PULSE
EFFICIENCY (%)
VIN = 5V
VOUT = 1.85V
90
80
VOUT = 1.10V
70
VOUT = 1.50V
60
50
0
5
10
15
20
25
30
35
40
LOAD CURRENT (A)
FIGURE 9. 5V INPUT EFFICIENCY AT DAC EXTREMES
PC Board Schematic
FIGURE 6. EXPANDED FRONT EDGE OF CURRENT PULSE
Figure 11 shows the main schematic. The Power Good
indicator circuit is shown in figure 13. Figure 12 shows the
schematic of the transient load generator.
The layout is shown in Figures 14 and 15, starting with the
silk screen in Figure 14. The Bill of Material is shown in Table 1.
Following the Bill of Materials is quick design guide.
PC Board Layout Considerations
Like all high current supplies where low voltage control
signals in the millivolt range must live with high voltage, high
current switching signals, PC board layout becomes crucial
in obtaining a satisfactory supply.
FIGURE 7. EXPANDED BACK EDGE OF CURRENT PULSE
3
ISL6560/62 Evaluation Board
Figure 10 shows a simplified diagram highlighting the critical
areas of a PC board layout. This diagram and the following
material represent goals to work towards during the layout
phase. Goals will be compromised during the layout process
due to component placement and space constraints. The
following text reviews these layout considerations in more
detail.
Current Sampling
1. Place the current sampling or sense resistor as close as
possible to the upper MOSFET drains. This is important
since the added inductance and resistance increase the
impedance and result in a reduction in drain voltage during
high peak pulse currents.
2. Current sense is critical, especially at lower current levels
where the current comparator threshold voltage is lower. A
good Kelvin connection requires that the voltage sample
must be taken at the RSENSE resistor ends and not at the
planes that the resistor is connected.
3. The lines to the current sense resistor should be parallel
and run away from the PHASE or PWM signals to prevent
coupling of spikes to the current comparator input that may
delay or advance triggering of the comparator. Parallel routing will work towards equal exposure for both lines, so that
the comparator common mode rejection characteristic will
reduce the influence of coupled noise.
4. Place the current sense filter network near the controller.
This will help reduce extraneous inputs to the comparator.
Voltage Sampling
1. To obtain optimum regulation use the Kelvin connection
for the output voltage sample as shown on the Functional
System Schematic Diagram of Figure 10. The ground connection, pin 9 of the ISL6560 should be connected to the
system ground at the load.
2. The two voltage sampling lines described in item 1 above
should also be routed away from any high current or high
pulse voltages such as the phase lines or pads. Doing this
will reduce the possibility of coupling undesired pulses into
the feedback signal and either modifying the output of the
error amplifier or, if of sufficient amplitude, spuriously triggering the current comparator by readjusting the threshold voltage.
Other Considerations
1. Keep the leads to the timing capacitor connected to pin
CT short and return the ground directly to pin 9.
2. When using a transistor to disable the converter by pulling
the CT pin to ground, place the transistor close to the CT pin
to minimize extraneous signal pickup.
3. As in all designs, keep decoupling networks near the pins
that must be decoupled. For example, the decoupling/filter
network on the FB input shown below. The series resistor
should be located next to the FB pin.
4. Large power and ground planes are critical to keeping
performance and efficiency high. Consider a 1mΩ resistance
in a 40A supply line. With 1.8V output, this results in slightly
over 2% power loss in a 72W supply.
12V
+VIN
Keep Leads Together
& Away from Output
{
INPUT
VID CODES
from
PROCSSOR{
1 VID4
VCC 16
2 VID3
REF 15
1 UGATE PHASE 8
3 VID2
CS- 14
2 BOOT
4 VID1 PWM1 13
5 VID0 PWM2 12
6 COMP
CS+ 11
7 FB
PWRGD 10
8 CT
GND 9
ISL6560
Locate
Parts
Next to IC
Locate
Parts
Next
to IC
Place Near Drains of the
Output Transistors
PVCC 7
3 PWM
VCC 6
4 GND
LGATE 5
+VCORE
HIP6601ECB
Try to return bypass
capacitors to ground
of lower MOSFETs
FIGURE 10. SCHEMATIC DIAGRAM SHOWING ONLY ONE CHANNEL OF “IDEAL” COMPONENT PLACEMENT
4
ISL6560/62 Evaluation Board
6 - 470µF
C15, C17-18
C29, C50-51
L3
5V - 12V
+VIN J4
TP7
1µH
4.7µF 10Ω
22k
R11
1nF
11
1
13
12
2
3
15
14
4
5
16
6
17
7
18
19
8
20Ω
R14
Q1 HUF76139
1 VID4
2 VID3
REF 15
1 UGATE PHASE 8
3 VID2
CS- 14
2 BOOT
4 VID1
PWM1 13
5 VID0
PWM2 12
7 FB
CS+ 11
330pF
C11
1nF
C10
GND 9
8 CT
330Ω
R7
TP4
TP11
PWRGD 10
150pF ISL6560
C14 U3
4.3k
R27
C20
C40 R6
VCC 16
6 COMP
C12
15k
R12
TP12
R13
15nF
SW1
TP9
SW2
5mΩ
2 - 4.7µF
C41-42
J5
12V
J6
9
10 20
ATX Connector
J1
L1
TP1
900nH
PVCC 7
3 PWM
VCC 6
4 GND
LGATE 5
Q2 HUF76145
HIP6601ECB 1µF
U1
C2
TP6
TP5
TP8
6 - 1500µF
C21, C24-28
+VCORE
J2
TP13
J3
Q3
HUF76139
TP10
100pF
C13
1k
R5
0.1µF
C1
1 UGATE PHASE 8
2 BOOT
0.1µF
C3
PVCC 7
3 PWM
VCC 6
4 GND
LGATE 5
TP2
L2
16 - 22µF
C19, C30,
C34-37,
900nH
C39
C45-49,
Q4 HUF76145
C60-63
HIP6601ECB 1µF
C4
U2
FIGURE 11. SCHEMATIC DIAGRAM OF A 40A SUPPLY USING THE ISL6560 CONTROLLER AND HIP6601 GATE DRIVERS
To CORE Plan
12V
4.7µF
C43
SW4
1 VDD
LO 8
2 HB
VSS 7
3 HO
LI 6
4 HS
HI 5
10k
R29
HIP2100
U4
732Ω
R26
324Ω
R16
732Ω
R32
D1
Q9 HUF78129
BAV99TA
D2
SW4A
12V
46.4k
R19
10k
R28
402
R20
Q7 2N7002
HUF78129
Q8
324Ω
R18 BAV99TA R22
0.05Ω
Current
Monitoring
10mV / Amp
R30
100
R23
33.2
TP14
R31
100
R24
0.05Ω
10µF
C44
To CORE GND Plan
FIGURE 12. SCHEMATIC DIAGRAM OF THE 40A PULSE GENERATOR ON THE POWER SUPPLY BOARD
5
ISL6560/62 Evaluation Board
To PWRGD
Pin 10 12V
120k
R9
GREEN
LED 1
RED
3.3k
R8
3.3k
R10
Q5
2N7002
Q6
2N7002
LED 1A
FIGURE 13. SCHEMATIC DIAGRAM OF THE POWER GOOD MONITORING CIRCUIT
CAll 1-888 Intersil
C
FIGURE 14. SILK SCREEN
6
ISL6560/62 Evaluation Board
FIGURE 15A. TOP COPPER
FIGURE 15C. POWER PLAN
FIGURE 15B. GROUND PLAN
FIGURE 15D. BOTTOM COPPER
FIGURES 15A-D. Showing ALL FOUR LAYERS OF THE PC BOARD
7
ISL6560/62 Evaluation Board
TABLE 1. Bill of Materials
Quantity
Reference
Part
PCB Footprint
Vendor
Part Number
2
C1,C3
0.1uF, 25V, X7R
Ceramic
P0805
Various
2
C2,C4
1uF, 25V, X7R
Ceramic
P0805
Various
2
C5,C8,
Not Populated
P1206
2
C7,C9
Not populated
P1206
2
C10, C12
1nF, 25V, X7R
Ceramic
P0805
Various
1
C11
330pF, 5%, 25V,
NPO Ceramic
P0805
Various
1
C13
100pF, 5%, 25V,
NPO Ceramic
P0805
Various
1
C14
150pF, 5%, 25V,
NPO Ceramic
P0805
Various
6
C15,C17,C18,C29,C50,C51
470uF, 16V
10x16
Rubycon
16
C19,C30,C34,C35,C36,C37,
C39,C45,C46,C47,C48,C49,
C60,C61,C62,C63
22uF, 6.3V, X5R
Ceramic
P1206
Various
1
C20
15nF, 10%, 25V,
X7R Ceramic
P0805
Various
6
C21,C24,C25,C26,C27,C28
1500uF, 4V
10x20
Sanyo
OS CON
6
C22,C23,C38,C31,C32,C33
Not Populated
10x20
5
C40,C41,C42, C43, C52
4.7uF,16V, Y5V
Ceramic
P1206
Various
1
C44
10uF, 10%, 6.3V,
X5R Ceramic
P1206
Various
1
C64
Not Populated
P1206
2
D1,D2
BAV99LT1
SM/SOT23_123
ZETEX
BAV99TA
1
J1
ATX CONNECTOR
ATX/CONN/20P
Molex or
Jameco
39-29-9202
147379
2
J3,J2
LUG
BINDING/POST_2
Burndy
KPA8CTP
1
J4
Red Binding Post
Post
Johnson
111-0702-001
1
J5
Black Binding Post
Post
Johnson
111-0703-001
1
J6
White Binding Post
Post
Johnson
111-0701-001
1
LED1
GREEN / RED
SMT/3MM/2.5MM/4LEAD
Panasonic
LN2162C13-(TR)
2
L1,L2
600nH 5T, AWG14
250WD/700LN
Micrometals
T60-8/90
1
L3
1uH
128WD/307OD
Micrometals
T50-52
2
Q1,Q3
HUF76139
TO263AB_M
Fairchild
2
Q2,Q4
HUF76145
TO263AB_M
Fairchild
3
Q5, Q6, Q7
2N7002
SM/SOT23_123
Various
2
Q9,Q8
HUF76129D3S
TO252AA/DPAK
Fairchild
2
R2,R4
Not populated
P1206
1
R5
1K, 5%
P0805
Various
1
R6
10Ω, 5%
P0805
Various
8
5T, AWG19
16ZA470-10x16
4SP1500M
ISL6560/62 Evaluation Board
TABLE 1. Bill of Materials (contiued)
1
R7
330Ω, 5%
P0805
Various
2
R10,R8
3.3K, 5%
P0805
Various
1
R9
120K, 5%
P0805
Various
1
R11
22K, 5%
P0805
Various
1
R12
15K, 5%
P0805
Various
1
R13
5mΩ, 1%
P2512
Panasonic
ERJM1WSF5M0U,
0.005 1%
1
R15
5mΩ, 1% o
fr
ISL6562 only
P2512 Not populated. Only
populated for ISL6562
operation
Panasonic
ERJM1WSF5M0U,
0.005 1%
1
R14
20Ω, 5%
P0805
Various
2
R16,R18
324Ω, 1%
P0603
Various
2
R26,R17
732Ω, 1%
P0603
Various
1
R19
46.4k, 1%
P0603
Various
1
R20
402 1%
P0603
Various
2
R21, R25
Not Populated
P2512
2
R22, R24
50mΩ, 1%
P2512
Vishay
1
R23
33.2Ω, 1%
P0603
Various
1
R27
4.3K, 5%
P0805
Various
2
R28, R29
10K, 5%
P0603
Various
2
R30, R31
100Ω, 1%
P0603
Various
1
SW1
SW DIP-5
DIPSW.100/10/W.300/L.550
CTS
2085
1
SW2
DPST
DPST_SWITCH
CK
GT11MSCK
1
SW4,SW4A
SW DIP-2
SPST_SWITCHs
Grayhill
76SB02
TP1,TP2,TP4,TP5,TP6,TP7
TP8,TP9,TP10,TP11,TP12,
TEST POINTS
TP
Keystone
5002
3
TP3, TP14
Test Probe
TP\PROBE-SOCKET
Tektronix
131-4353-00
2
U1,U2
HIP6601ECB
8L\EPAD\SOIC
Intersil
1
U3
ISL6560/62 Using an
ISL6562 - Populate
R15 with resistor
16L\SOIC
Intersil
1
U4
HIP2100
8L\SOIC
Intersil
1
PC Board
4 layers
2 0z Copper
Various
11
9
WSL2512, 0.05 1%
ISL6560/62 Evaluation Board
ISL6560 Supply Design Sequence
The ISL6560 data sheet describes in more detail the following equations. There are several changes from the computations in
the body of the data sheet. First, an operating frequency of 400kHz was chosen. Next, this design sequence shows the method of
setting the initial no load voltage at the DAC setting and offsetting the no load voltage 15mV above the programmed DAC voltage.
A. Specifications:
G. Input Capacitor’s RMS Current:
Use the curve of Figure B
CURRENT MULTIPLIER
Output Current:
40A
Input Voltage:
12V
Output Voltage: VDAC + 15mV
Output Voltage for Calculations:
VDAC = 1.8V + 15mV
Droop Voltage: 65mV
Oscillator Frequency: 400kHz (fSW)
B. Calculate ROUT:
0.2
0.1
0
0.1
0
0.2
0.3
DUTY CYCLE (VO / VIN)
0.4
0.5
FIGURE B. CURRENT MULTIPLIER vs. DUTY CYCLE
V DROOP
65mV
R OUT = ---------------------------- = ---------------- = 1.63mΩ
I OUT
40A
For 40A with a duty cycle (D) of:
C. Determine Frequency Setting Capacitor CT:.
3000
FREQUENCY (kHz)
0.3
V OUT
1.8V
D = ----------------- = ------------ = 0.15
V IN
12V
The multiplier from Figure B is 0.24.
I RMS = 0.24 × 40A = 9.6A
1000
Pensioned 470µF, 16V Rubdown ZA series capacitors
have a RMS current rating of 1.6A.
Six capacitors were selected.
100
0
50 100 150 200 250 300 350 400
CAPACITOR CT (pF)
450 500
FIGURE A. OSCILLATOR FREQUENCY vs. TIMING CAPACITOR
From curve above, for 400kHz use 120pF.
H. Current Sense Resistor (RSENSE):
V CS ( TH )MIN
142mV
R SENSE = ------------------------------------------------ = ------------------------- = 5.07mΩ
20A + 8A
I OUT I RIPPLE
--------------- + ------------------------2
2
Use a 5mΩ resistor
D. Select Inductor Ripple Current (∆IL):
I. RSENSE Dissipation:
Choose 40% of IOUT
∆I L = 40A × 0.4 = 16A
Or 8A / Channel
E. Determine the Inductors:
I RMS = I PEAK D
2
∴Power = I P × D × R SENSE
Where: IP = 20A + 4A = 24A (Using half 0f ripple current
2
Power = 24A × 0.15 × 5mΩ
V IN – V OUT V OUT
12V – 1.8V
1.8V
L = ---------------------------------- × ----------------- = ----------------------------------- × -----------200kHz × 8A 12V
f SW
V IN
------------ × ∆I
L
2
= 956nH
= 432mW
Used a 1W resistor
J. RL Selection:
ni × R SENSE
12.5 × 5mΩ
R L = ------------------------------------------ = -------------------------------------------------------- = 8.7kΩ
gm × R OUT × 2
2.2mS × 1.63mΩ × 2
ni = ∆VCOMP / VCS (from data sheet)
am Amplifier Gain = gm × RL = 2.2mS × 8.7k = 19.1
F. Output Capacitors:
Capacitor ESR ≅ R OUT = 1.63mΩ
Sonya 1500µF, 4V OS-CON Capacitors
have an ESR < 10mΩ
Six capacitors < 1.66mΩ
Total Capacitance = 9mF
K. VSET Computation for No Load Voltage = DAC:
VOUT, the no load voltage programed to the DAC voltage
V S E T, the voltage set at the COMP pin
I RIPPLE × R SENSE × ni
VSET = 1V + ---------------------------------------------------------------------2
8A × 5mΩ × 12.5
= 1V + --------------------------------------------2
= 1V + 250mV = 1.25V
10
ISL6560/62 Evaluation Board
L. gm Amplifier Output Load Network:
VREF = 3V
V REF
R U = ----------------- × R L
V SET
R U || R B = R L
VREF = 3V
3V
R U = ---------------- × 8.7k = 20.9k
1.25V
RU
RB
N. gm Amplifier Output Load Network:
R U || R B = R L
3V
R U = ---------------- × 8.7k = 16.9K
1.54V
RU
To COMP pin,
this voltage is VSET
RB
To COMP pin,
this voltage is VSET
V SET
R B = ---------------------------------------- × R U
V REF – V SET
V SET
R B = ---------------------------------------- × R U
V REF – V SET
1.25V
R B = ----------------------------- × 20.9k = 14.9k
3V – 1.25V
M. VSET Computation for No Load Voltage = DAC +15mV:
1.54V
R B = ----------------------------- × 16.9k = 17.8k
3V – 1.54V
O. CC and RC Selection:
R OUT × C OUT
1.63mΩ × 9mF
C C = ------------------------------------------ = ----------------------------------------- = 1.68nF
8.7k
RL
VOUT, no load voltage to be set 15mV above
programed DAC voltage
VREF = 3V
Added output voltage of the gm amplifier will be:
15mV X gm Amplifier gain = 15mv x 19.1 = 287mV
I RIPPLE × R SENSE × ni
V SET = 1V + ---------------------------------------------------------------------- + 287mV
2
8A × 5mΩ × 12.5
= 1V + --------------------------------------------- + 287mV
2
= 1V + 250mV + 287mV = 1.536V
V REF
R U = ----------------- × R L
V SET
R U || R B = R L
RU
To COMP pin
CC
CC
RC
AC Equivalent
COMP pin
RC
RB
RL
RC = 0.5 x RL = 0.5 x 8.7k = 4.35k
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