XR77103 Datasheet, PDF (16/28 Pages) Exar Corporation – 3-Output Programmable Buck Regulator

XR77103
Applications Information (Continued)
Frequency Compensation
In order to properly frequency compensate the device,
the following component selection is recommended.
The table below is for 2A loads.
V_IN
V_OUT
L
C_OUT
(V)
(V)
(μH)
(µF)
500kHz Switching Frequency
12/5.0
1.0
2.2
22 x 3
12/5.0
1.2
2.2
22 x 3
12/5.0
1.5
3.3
22 x 3
12/5.0
1.8
3.3
22 x 2
12/5.0
2.5
4.7
22 x 2
12/5.0
3.3
4.7
22 x 1
12
5.0
6.8
22 x 1
1MHz Switching Frequency
5.0
1.0
1.5
22 x 3
5.0
1.2
1.5
22 x 3
5.0
1.5
1.5
22 x 2
12/5.0
1.8
1.5
22 x 2
12/5.0
2.5
3.3
22 x 1
12/5.0
3.3
3.3
22 x 1
12
5.0
3.3
22 x 1
R_COMP C_COMP
(kΩ)
(nF)
10
4.7
10
4.7
20
4.7
20
4.7
20
4.7
20
4.7
20
4.7
10
4.7
10
4.7
20
4.7
20
4.7
20
4.7
20
4.7
20
4.7
For configurations not listed above contact
[e-mail].
Switching Frequency Setting
Switching frequency can be set from 300kHz to 2.2MHz
with a 100kHz step. Lower 5 bits of the register 09h are
allocated to setting the switching frequency.
Current Limit Setting
Peak inductor current limit level of each converter can
be set individually from 1A to 4A with a 0.5A step. Lower
3 bits of the registers 06h, 07h and 08h are allocated
to setting the peak inductor current limit of Buck 1,
Buck 2 and Buck 3 respectively.
Soft-start Time Setting
Soft-start time of each converter can be set individually
(see Figure 36). Lower 3 bits of the registers 03h, 04h and
05h are allocated to setting the soft-start time of Buck 1,
Buck 2 and Buck 3 respectively.
The soft-start times are relative to switching frequency.
They scale with switching frequency.
At switching frequency set at 1MHz, the available soft-start
range is from 0.5ms to 4ms with a 0.5ms step.
At switching frequency set at 500kHz, the available
soft-start range is from 1ms to 8ms with a 1ms step.
EN
VOUT1
VOUT2
tDLY1 tSS3
VOUT3
tDLY2 tSS2
tDLY3
tSS3
Figure 37. Programmable Soft-start Time and
Delay Time of each Converter
Delayed Start-Up
All outputs start up once EN pin is high and select bits of
each converter are set. If a delayed start-up is required
on any of the buck converters, set delay time of each
converter. The bits [6:4] of the registers 03h, 04h and 05h
are allocated to setting delay time of Buck 1, Buck 2 and
Buck 3 respectively.
The soft-start delay times are relative to switching frequency.
They scale with switching frequency.
At switching frequency set at 1MHz, the available soft-start
delay time range is from 0ms to 35ms with a 5ms step.
At switching frequency set at 500kHz, the available
soft-start delay time range is from 0ms to 70ms with a
10ms step.
REV1B
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