ADP1873ARMZ-0.3-R7 Analog Devices Inc, ADP1873ARMZ-0.3-R7 Datasheet - Page 20

• Manufacturer Part Number: ADP1873ARMZ-0.3-R7
• Description: 300kHz, Light Load Eff Enabled
• Manufacturer: Analog Devices Inc

Specifications of ADP1873ARMZ-0.3-R7

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 300kHz
• Duty Cycle: 84%
• Voltage - Supply: 2.75 V ~ 20 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Frequency-max: 300kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ADP1873ARMZ-0.3-R7TR

ADP1872/ADP1873
Table 6. Valley Current Limit Program
R
(mΩ)
1.5
2
2.5
3
3.5
4.5
5
5.5
10
15
18
1
Refer to Figure 70 for more information and a graphical representation.
ON
Figure 70. Valley Current-Limit Value vs. R
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
47 kΩ
A
31.0
26.0
9
7
5
3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
CS
RES = 100kΩ
= 3 V/V
A
CS
= 24V/V
for Each Programming Resistor (RES)
22 kΩ
A
23.3
15.5
13.0
CS
Valley Current Level
= 6 V/V
RES = NO RES
A
CS
R
ON
CURRENT
= 12V/V
(mΩ)
ZERO
CLIM
Open
A
39.0
33.4
26.0
23.4
21.25
11.7
7.75
6.5
HS
ON
CS
of the Lower Side MOSFET
= 12 V/V
Figure 72. Idle Mode Entry Sequence Due to Current-Limit Violations
1
REPEATED CURRENT LIMIT
RES = 22kΩ
A
RES = 47kΩ
VIOLATION DETECTED
A
CS
CS
= 6V/V
= 3V/V
A
38.9
29.2
23.3
19.5
16.7
13
11.7
10.6
5.83
7.5
3.25
100 kΩ
CS
= 24 V/V
Rev. A | Page 20 of 40
A PREDETERMINED NUMBER
OF PULSES IS COUNTED TO
ALLOW THE CONVERTER
The valley current limit is programmed as outlined in Table 6
and Figure 70. The inductor chosen must be rated to handle the
peak current, which is equal to the valley current from Table 6
plus the peak-to-peak inductor ripple current (see the Inductor
Selection section). In addition, the peak current value must be
used to compute the worst-case power dissipation in the MOSFETs
(see Figure 71).
HICCUP MODE DURING SHORT CIRCUIT
A current-limit violation occurs when the current across the
source and drain of the lower side MOSFET exceeds the current-
limit setpoint. When 32 current-limit violations are detected,
the controller enters idle mode and turns off the MOSFETs for
6 ms, allowing the converter to cool down. Then, the controller
re-establishes soft start and begins to cause the output to ramp
up again (see Figure 72). While the output ramps up, COMP is
monitored to determine if the violation is still present. If it is still
present, the idle event occurs again, followed by the full-chip
power-down sequence. This cycle continues until the violation
no longer exists. If the violation disappears, the converter is
allowed to switch normally, maintaining regulation.
TO COOL DOWN
Figure 71. Valley Current-Limit Threshold in Relation to Inductor Ripple Current
INDUCTOR
CURRENT
0A
ΔI = 33%
OF 30A
VALLEY CURRENT LIMIT
THRESHOLD (SET FOR 25A)
35A
30A
REINITIALIZED TO
MONITOR IF THE
SOFT START IS
STILL EXISTS
VIOLATION
MAXIMUM DC LOAD
OF 32.25A
ΔI = 45%
CURRENT
39.5A
32.25A
ΔI = 65%
OF 37A
49A
37A
OUTPUT
SWING
COMP
OUTPUT
COMP
2.4V
1V