DC1297B Linear Technology, DC1297B Datasheet - Page 12

• Manufacturer Part Number: DC1297B
• Description: BOARD EVAL LTM4612
• Manufacturer: Linear Technology
• Series: µModuler

Specifications of DC1297B

• Design Resources: LTM4612 Spice Model LTM4612 Gerber Files DC1297B Design Files DC1297B Schematic
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Power - Output: -
• Voltage - Output: 3.3V, 5V ,12V
• Current - Output: 5A
• Voltage - Input: 5 ~ 36 V
• Regulator Topology: Buck
• Frequency - Switching: 850kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LTM4612
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

LTM4612
applicaTions inForMaTion
Operating Frequency
The operating frequency of the LTM4612 is optimized to
achieve the compact package size and the minimum
output ripple voltage while still providing high efficiency.
As shown in Figure 2, the frequency is linearly increased
with larger output voltages to keep the low output cur-
rent ripple. Figure 3 shows the inductor current ripple DI
with different output voltages. In most applications, no
additional frequency adjusting is required.
If lower output ripple is required, the operating frequency
f can be increased by adding a resistor R
pin and SGND, as shown in Figure 19.
12
f =
1.5 • 10
Figure 2. Operating Frequency vs Output Voltage
1200
1000
800
600
400
200
2
−10
V
4
(
OUT
R
fSET
6
|| 93.1k
8
V
OUT
(V)
10
)
12
14
fSET
4612 F02
16
between f
SET
For output voltages more than 12V, the frequency can be
higher than 1MHz, thus reducing the efficiency significantly.
Additionally, the 500ns minimum off time (400ns + 100ns
for margin) normally limits the operation when the input
voltage is close to the output voltage. Therefore, it is rec-
ommended to lower the frequency in these conditions by
connecting a resistor (R
shown in Figure 20.
The load current can affect the frequency due to its constant
on-time control. If constant frequency is a necessity, the
PLLIN pin can be used to synchronize the frequency of
the LTM4612 to an external clock, as shown in Figures
21 to 23.
f =
Figure 3. Inductor Current Ripple vs Output Voltage
5 • 10
3.5
3.0
2.5
2.0
1.5
1.0
0.5
−11
2
⎛
⎜
⎝
R
3 • R
4
V
fSET
OUT
fSET
6
− 2 • 93.1k
fSET
V
V
8
OUT
IN
• 93.1k
) from the f
= 20V
(V)
10
12
V
⎞
⎟
⎠
IN
V
= 36V
IN
14
= 28V
SET
4612 F03
16
pin to V
IN
4612fb
, as