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Charge Pump Voltage Multiplier Calculator

Calculate Dickson charge pump output voltage, loaded voltage, output ripple, and efficiency for switched-capacitor voltage multiplier circuits

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Formula

Voc=Vin×(N+1),Vout=Voc−N×Iout/(f×C)V_oc = V_in × (N+1), V_out = V_oc − N × I_out / (f × C)
V_in— Input voltage (V)
N— Number of stages
I_out— Output current (A)
f— Switching frequency (Hz)
C— Pump capacitance (F)

How It Works

The charge pump voltage calculator determines output voltage, current capability, and efficiency for capacitive DC-DC conversion — essential for gate drivers, RS-232 interfaces, flash memory programming, and low-power boost applications. Analog IC designers, portable device engineers, and mixed-signal developers use this tool to achieve voltage multiplication without magnetic components. According to TI application note SLVA517, charge pumps transfer energy by charging a flying capacitor to Vin during one phase and stacking it in series with Vin during the second phase, ideally producing Vout = N × Vin for an N× multiplier. The charge pump topology is analyzed in detail in Erickson & Maksimovic 'Fundamentals of Power Electronics' (3rd ed.) Chapter 5 (Discontinuous Conduction Mode) and the Analog Devices 'Linear Circuit Design Handbook' (2008) Chapter 4. Real-world output voltage drops due to switch resistance and capacitor ESR: Vout = N×Vin - Iout×(N×Rsw + N²×ESR/fsw). Per Maxim Integrated application note AN-725, unregulated charge pumps achieve 80-90% efficiency at optimal load, dropping to 50-60% at light load. Regulated charge pumps (TI LM2776) maintain 85% efficiency across 1-100 mA load range by adjusting switching frequency. Maximum output current depends on flying capacitor value: Iout_max ≈ C × fsw × Vin for voltage doublers, making higher capacitance or frequency necessary for increased current capability.

Worked Example

Design a voltage doubler for MOSFET gate drive from 5 V logic supply. Requirements: 10 V output, 50 mA peak current, <100 mV ripple. Step 1: Verify multiplication — Doubler: Vout_ideal = 2 × 5 V = 10 V. Step 2: Calculate flying capacitor — For Iout = 50 mA with 200 kHz switching: Cfly = Iout/(fsw × ΔV) = 50m/(200k × 0.1) = 2.5 µF minimum. Use 4.7 µF X5R ceramic. Step 3: Estimate voltage drop — Assume Rsw = 3 Ω (typical TI TPS60403): Vdrop = 50m × (2×3 + 2²×10m/200k) = 300 mV. Vout = 10 - 0.3 = 9.7 V. Step 4: Select output capacitor — Cout = Iout/(fsw × ΔVripple) = 50m/(200k × 0.1) = 2.5 µF. Use 10 µF for margin. Step 5: Verify efficiency — η = Vout/(2×Vin) = 9.7/10 = 97% at no load, dropping to 85-90% at 50 mA. Step 6: Select IC — TI LM2775 (doubler, 150 mA, 95% peak efficiency) with integrated soft-start and thermal shutdown.

Practical Tips

  • ✓Per Linear Technology (now ADI) application note AN-88, use regulated charge pumps for noise-sensitive applications — unregulated pumps generate 20-50 mV ripple that couples into adjacent analog circuits
  • ✓Add small series resistance (1-10 Ω) in the output for improved transient response and to damp LC resonance between output capacitor ESL and load capacitance
  • ✓For negative voltage generation, use inverting charge pump topology (Maxim MAX1044) — achieves Vout = -Vin with same efficiency as positive doublers

Common Mistakes

  • ✗Using electrolytic capacitors — ESR of 100-500 mΩ causes 10× higher voltage drop than ceramics; charge pumps require low-ESR (5-20 mΩ) X5R/X7R ceramics for rated performance
  • ✗Ignoring capacitor DC bias derating — 10 µF/10V X5R at 9 V DC retains only 20-30% of capacitance; either use 16 V rated capacitor or 3× larger nominal value
  • ✗Exceeding output current rating — charge pump output impedance is ~1/(fsw × C); at 200 kHz with 1 µF, Zout = 5 Ω, causing 500 mV drop at 100 mA

Frequently Asked Questions

Per TI SLVA517, a charge pump uses capacitors and switches to transfer charge in discrete packets, achieving voltage multiplication or inversion without inductors. During phase 1, flying capacitor charges to Vin; during phase 2, it's reconfigured to add (doubler), subtract (inverter), or series stack (tripler/quadrupler). Advantages: no magnetic EMI, compact size, low cost. Disadvantages: limited current (typically <500 mA), efficiency drops at high Vout/Vin ratios.
Per Maxim AN-725: Unregulated doublers: 80-90% peak efficiency at matched load impedance, Vout ≈ 2×Vin - I×Rsw. Regulated charge pumps: 85-95% using PFM or PWM regulation. Fractional converters (3/2×, 2/3×): 90-95% efficiency due to lower switch stress. Inverters (-1×): 75-85% due to two charge transfer cycles. Efficiency degrades rapidly when output voltage differs significantly from ideal ratio.
Primary applications: (1) Gate drivers — 12 V bootstrap from 5 V for MOSFET Vgs, (2) RS-232 transceivers — ±12 V from 3.3 V for MAX232 family, (3) Flash/EEPROM programming — 12-20 V from 3.3 V for write operations, (4) LCD bias — negative voltage for display contrast, (5) White LED drivers — boost 3.7 V Li-ion to 4.5 V for 4 series LEDs. Annual market: >$500M, with 15% CAGR in IoT/wearables per IC Insights.
Iout_max = Cfly × fsw × ΔV, where ΔV is acceptable flying capacitor voltage sag. For 10 µF at 1 MHz with 0.5 V sag: Iout_max = 10µ × 1M × 0.5 = 5 A theoretical. Practical limits: switch current rating (typically 100-500 mA), package thermal limits. High-current charge pumps (TI TPS60150, 400 mA) use multiple paralleled stages or larger switches.
Per TI SLVA517: (1) Increase output capacitance — doubling Cout halves ripple, (2) Increase switching frequency — doubling fsw halves ripple (limited by driver losses), (3) Use regulated topology — PFM maintains constant output with variable frequency, (4) Add post-regulator — ferrite bead + capacitor provides 20 dB additional filtering. Target ripple: <50 mV for digital logic, <10 mV for analog/RF loads.

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