ADP1621ARMZ-R7 Analog Devices Inc, ADP1621ARMZ-R7 Datasheet - Page 17

• Manufacturer Part Number: ADP1621ARMZ-R7
• Description: IC CTRLR DC/DC PWM STEPUP 10MSOP
• Manufacturer: Analog Devices Inc
• Type: Step-Up (Boost)r

Specifications of ADP1621ARMZ-R7

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Current - Output: 1A
• Frequency - Switching: 100kHz ~ 1.5MHz
• Voltage - Input: 2.9 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Primary Input Voltage: 5.5V
• No. Of Outputs: 1
• Output Current: 1A
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Frequency Max: 1.5MHz
• Termination Type: SMD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: ADP1621-EVALZ - BOARD EVALUATION FOR ADP1621
• Voltage - Output: -
• Power - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: ADP1621ARMZ-R7; ADP1621ARMZ-R7TR

frequency occurs well below the frequency of the RHP zero. The
location of the RHP zero is determined by the following equation:
where f
load resistance or the output voltage divided by the load current.
To stabilize the regulator, ensure that the regulator crossover
frequency is less than or equal to one-fifth of the RHP zero
frequency and less than or equal to one-fifteenth of the switching
frequency. For an initial practical design, choose the crossover
frequency f
and
where f
frequency.
The regulator loop gain is
where A
voltage (typically 1.215 V), V
D is the duty cycle, g
gain (typically 300 μS), Z
from COMP to GND, n is the current-sense amplifier gain
(typically 9.5), R
the impedance of the load and output capacitor. In the case of
lossless current sensing, as shown in Figure 28, R
on resistance, R
R
Figure 29.
To determine the crossover frequency, it is important to note
that at that frequency the compensation impedance, Z
dominated by Resistor R
is dominated by the impedance of the output capacitor, C
When solving for the crossover frequency, the equation is
simplified to
where f
resistor, and C
Solving for R
|
A
V
V
A
CS
VL
OUT
VL
FB
represents the external current-sense resistor, as shown in
=
R
f
f =
f =
= |
Z
C
C
×
COMP
Z,RHP
C
V
C
,
V
RHP
(
VL
1
is the crossover frequency, and f
OUT
is the crossover frequency, R
FB
−
is the loop gain, V
f
15
f
is the RHP zero frequency, and R
C
SW
Z
=
D
=
,RHP
5
to be the lower of
COMP
×
(
)
OUT
1
2
(
DSON
×
1
π
−
CS
g
−
×
D
is the output capacitance.
gives
m
is the current-sense resistance, and Z
, of the external power MOSFET. Otherwise,
D
f
)
×
C
2
m
)
V
×
R
×
×
is the error amplifier transconductance
FB
COMP
g
COMP
R
2
C
COMP
π
m
×
LOAD
OUT
×
×
(
1
is the impedance of the RC network
|
×
L
FB
, and the output impedance, Z
−
OUT
Z
×
n
D
COMP
is the feedback regulation
n
×
is the regulated output voltage,
×
)
1
R
×
R
CS
g
CS
|
m
×
COMP
×
×
n
2
V
×
SW
π
OUT
is the compensation
1
R
×
LOAD
is the switching
CS
f
C
1
is the equivalent
×
CS
×
|
C
is equal to the
Z
OUT
OUT
COMP
=
|
OUT
1
OUT
, is
OUT
is
(25)
(26)
(27)
(28)
(29)
(30)
Rev. A | Page 17 of 32
.
,
Once the compensation resistor, R
formed by the resistor and compensation capacitor, C
one-fourth of the crossover frequency, or
Capacitor C2 is chosen to cancel the zero introduced by the output
capacitance ESR. Thus, C2 should be set to (see Figure 31)
where ESR represents the ESR of C
For low ESR output capacitors, such as ceramic capacitors, C2
is small, generally in the range of 10 pF to 400 pF. Because of the
parasitic inductance, resistance, and capacitance of the PCB layout,
the R
observing the load transient response of the ADP1621 to establish a
stable operating system and achieve optimal transient performance.
For most applications, R
and C
SLOPE COMPENSATION
The ADP1621 includes a circuit that allows adjustable slope
compensation. Slope compensation is required by current-
mode regulators to stabilize the current-control loop when
operating in continuous conduction and the switching duty
cycle is greater than 50%.
Slope compensation is achieved by internally forcing a ramping
current source out of the CS current-sense pin. By placing a resistor
between the CS pin and the current sensing device (the drain of
the external MOSFET in the case of lossless current sensing or
the source of the MOSFET if a current-sense resistor is used), a
voltage is developed across the resistor that is proportional to
the slope-compensation current.
To ensure stability of the current-mode control loop, use a
compensation voltage slope that is equal to or greater than one-
half of the current-sense representation of the inductor current
downslope. Therefore, it follows that
where R
compensation current, f
current-sense resistor, V
forward-voltage drop of the diode, V
the minimum off time, and L is the power-stage inductor. In the
case of lossless current sensing, R
C
C
2
COMP
COMP
COMP
×
2
S
R
=
is the slope-compensation resistor, I
, C
S
is in the range of 100 pF to 30 nF.
ESR
×
=
COMP
1
π
R
−
COMP
×
×
REF
I
Figure 31. Compensation Components
t
SC,PK
f
, and C2 values might need to be adjusted by
2
OFF,
C
C
OUT
×
2
MIN
R
×
COMP
OUT
f
g
×
SW
COMP
SW
m
f
is the regulated output voltage, V
is the switching frequency, R
SW
is in the range of 5 kΩ to 100 kΩ,
COMP
>
3
R
CS
CS
COMP
OUT
IN
is equal to the on resistance,
R
×
C
is the input voltage, t
COMP
.
COMP
V
, is known, set the zero
OUT
SC,PK
+
C2
V
L
D
is the peak slope-
−
ADP1621
V
IN
COMP
CS
OFF,MIN
is the
D
, to
is the
(31)
(32)
(33)
is