JAJSNC2 データシート

JAJSNC2B March 2023 – January 2024 TPS56836 , TPS56837 , TPS56838

PRODUCTION DATA

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）

RPA|10
- MPQF515

サーマルパッド・メカニカル・データ

発注情報

7.2.2.3 Output Filter Selection

The LC filter used as the output filter has double pole at:

Equation 7.

f_{p} = \frac{1}{2 π \times \sqrt{L_{O U T} \times C_{O U T}}}

At low frequencies, the overall loop gain is set by the output set-point resistor divider network and the internal gain of the device. The low frequency phase is 180 degrees. At the output filter pole frequency, the gain rolls off at a –40dB per decade rate and the phase drops rapidly. D-CAP3 control mode introduces a high frequency zero that reduces the gain roll off to –20dB per decade and increases the phase to 90 degrees one decade above the zero frequency. The inductor and capacitor for the output filter must be selected so that the double pole of Equation 7 is located below the high frequency zero but close enough that the phase boost provided be the high frequency zero provides adequate phase margin for a stable circuit. To meet this requirement use the values recommended in Table 7-2.

Table 7-2 Recommended Component Values

Switching Frequency (kHz)	Output Voltage⁽¹⁾ (V)	R6⁽²⁾(kΩ)	R7 (kΩ)	L1 (µH)	C_OUT⁽³⁾			C10 ⁽⁴⁾(pF)
Switching Frequency (kHz)	Output Voltage⁽¹⁾ (V)	R6⁽²⁾(kΩ)	R7 (kΩ)	L1 (µH)	Minimum	Typical	Maximum	C10 ⁽⁴⁾(pF)
500	1.05	7.5	10	1	22uF × 1	22uF × 3	22uF × 10
	1.8	20	10	1.5	22uF × 1	22uF × 3	22uF × 10
	3.3	45.3	10	2.2	22uF × 1	22uF × 3	22uF × 10	100-200 (150 typical)
	5	73.2	10	3.3	22uF × 1	22uF × 2	22uF × 10	100-200 (150 typical)
	9	140	10	4.7	22uF × 1	22uF × 2	22uF × 10	50-150 (100 typical)
	12	383	20	5.6	22uF × 1	22uF × 2	22uF × 10	30-100 (30 typical)
800	1.05	7.5	10	0.68	22uF × 1	22uF × 3	22uF × 10
	1.8	20	10	1	22uF × 1	22uF × 3	22uF × 10
	3.3	45.3	10	1.5	22uF × 1	22uF × 3	22uF × 10	100-200 (150 typical)
	5	73.2	10	2.2	22uF × 1	22uF × 2	22uF × 10	100-200 (150 typical)
	9	140	10	3.3	22uF × 1	22uF × 2	22uF × 10	50-150 (100 typical)
	12	383	20	3.3	22uF × 1	22uF × 2	22uF × 10	30-100 (30 typical)
1200	1.05	7.5	10	0.47	22uF × 1	22uF × 3	22uF × 10
	1.8	20	10	0.68	22uF × 1	22uF × 3	22uF × 10
	3.3	45.3	10	1	22uF × 1	22uF × 3	22uF × 10	100-200 (150 typical)
	5	73.2	10	1.5	22uF × 1	22uF × 2	22uF × 10	1100-200 (150 typical)
	9	140	10	2.2	22uF × 1	22uF × 2	22uF × 10	50-150 (100 typical)
	12	383	20	2.2	22uF × 1	22uF × 2	22uF × 10	30-100 (30 typical)

(1) Please use the recommended L1 and C_OUT combination of the higher and closest output rail for unlisted output rails.

(2) R6 = 0Ω for V_OUT = 0.6V.

(3) C_OUT in this data sheet is using Murata GRM32ER71E226KE15L 25VDC capacitor. Recommend to use the same effective output capacitance. The effective capacitance is defined as the actual capacitance under DC bias and temperature, not the rated or nameplate values. All high value ceramic capacitors have a large voltage coefficient in addition to normal tolerances and temperature effects. A careful study of bias and temperature variation of any capacitor bank must be made to make sure that the minimum value of effective capacitance is provided. Refer to the information of DC bias and temperature characteristics from manufacturers of ceramic capacitors. Higher than Cout_max capacitance is allowed by careful tuning the feedforward compensation.

(4) R8 and C10 can be used to improve load transient response or improve the loop-phase margin. Optimizing Transient Response of Internally Compensated DCDC Converters with Feed-forward Capacitor application report is helpful when experimenting with a feed-forward capacitor.

The inductor peak-to-peak ripple current, peak current and RMS current are calculated using Equation 8, Equation 9, and Equation 10. The inductor saturation current rating must be greater than the calculated peak current and the RMS or heating current rating must be greater than the calculated RMS current.

Use 500kHz for f_SW. Make sure the chosen inductor is rated for the peak current of Equation 9 and the RMS current of Equation 10.

Equation 8.

{I l}_{p - p} = \frac{V_{O U T}}{V_{I N (M A X)}} \times \frac{V_{I N (M A X)} - V_{O U T}}{L_{O U T} \times F s w}

Equation 9.

{I l}_{P E A K} = I_{O} + \frac{{I l}_{p - p}}{2}

Equation 10.

I_{L O (R M S)} = \sqrt{{I_{O}}^{2} + \frac{1}{12} \times {I l}_{p - p}^{2}}

For this design example, the calculated peak current is 9.13A and the calculated RMS current is 8.03A. The inductor used is Wurth 744325330 with saturation current 15A and rating current 9.7A.

The capacitor value and ESR determines the output voltage ripple. The TPS56837 is intended to use with ceramic or other low ESR capacitors. Use Equation 11 to determine the required RMS current rating for the output capacitor.

Equation 11.

I_{C O (R M S)} = \frac{V_{O U T} \times (V_{I N} - V_{O U T})}{\sqrt{12} \times V_{I N} \times L_{O U T} \times F s w}

For this design, two MuRata GRM32ER71E226KE15L 22µF output capacitors are used so that the effective capacitance is 35µF at DC biased voltage of 5V. The calculated RMS current is 0.63A and each output capacitor is rated for 4A.