Boost (Step-Up) Circuit Design | GREEN Digital Power

Boost chip scheme for 1V~5V input, 2~5.5V output:

1.1Scheme: SY7080ABC, 0.9~4V input, 2~4V output, integrated boost chip solution

Input voltage: 0.9V - 4V

Output voltage: 2.5V - 4V
Current limit: 1.8A
Switching frequency: 1.2MHz

Max efficiency: 90% (Vin=1.5V, Vout=3.3V 0.2A)

Quiescent current: <1µA
Rds(on): 90mΩ/200mΩ (main/sync)

Inductor: L>=Vin*(Vout-Vin)/(2*Vout*Iout*fs); ensure saturation current > 1.5*Iout

Capacitors: ceramic, solid polymer, or high-frequency low-ESR electrolytic
Chip package: SOT23-6
Applications: portable devices powered by one or two NiMH or alkaline cells.
Chip reference price: RMB 1.5

Typical application circuit:

Boost (Step-Up) Circuit Design — figure 1 — FIG.01 · CLICK TO ENLARGE

1.2Scheme: SY7069ADC - 1.8V~5V input, 2~5V output, integrated boost chip solution

Input voltage: 1.8V – 5.5V

Output voltage: 2.5V – 5.5V
Current limit: 3.0A. Note: with TI's TPS61236 the current limit can reach 8A
Switching frequency: 1MHz
Max efficiency: 94% (Vin=3.6V, Vout=5V 1A); with TI's TPS61236 up to 97%
Quiescent current: <1µA
Rds(on): 50mΩ/90mΩ (main/sync)

Inductor: L1= (Vout-Vin)*Vin/(Vout*0.2*Iout*fs); ensure saturation current ≥ 1.2*Iout

Capacitors: ceramic, solid polymer, or high-frequency low-ESR electrolytic
Chip package: SOT23-6

Applications: single Li-ion cell powered devices, power banks

Chip reference price: RMB 1

Typical application circuit:

Boost (Step-Up) Circuit Design — figure 2 — FIG.02 · CLICK TO ENLARGE

Boost chip scheme for 3V~25V input, 4~25V output:

Many vendors offer integrated boost chips in this voltage/current range; here is the cost-effective SY7208ABC:

Chip: SY7208ABC, reference price RMB 1

Input voltage: 3V ~ 25V

Output voltage: 4V ~ 25V
Current limit: 2.5A. Note: for higher current, TI's TPS61288 with 15A limit is recommended
Switching frequency: fixed 1MHz
Peak efficiency: >90% (5V input, 12V 0.5A output)
Quiescent current: <1µA
Rds(on): 150mΩ
Chip package: SOT23-6
Features: wide input range, 1µA shutdown current, 1MHz high frequency, built-in 150mΩ MOSFET
Design case: 5V→12V/0.5A

Power inductor calculation: L1= (Vout-Vin)*Vin/(Vout*0.2*Iout*fs); note saturation current ≥1.2*Iout

Input/output capacitors: high-frequency low-ESR electrolytic

Applications: automotive devices, industrial control, solar PV, power banks

Typical application circuit:

Boost (Step-Up) Circuit Design — figure 3 — FIG.03 · CLICK TO ENLARGE

3General-purpose boost scheme (controller + external MOS)

For high-voltage output and other high-current boost circuits, use the general-purpose BOOST scheme below, formed by the SY7901 controller + external MOS:

Controller: SY7901DBC, reference price around RMB 2
Input voltage: >5V; note the SY7901 supply voltage must not exceed 25V — above 25V use a BUCK stage to power the IC
Output voltage: >8V
Output current: depends on the external MOSFET.
Peak efficiency: 90% (20V input, 40V 2A output)

Features: 500kHz, external MOSFET, no synchronous rectification, complete protection

MOSFET selection: Vds>1.3*Vout_max; Rds(on) and switching speed as small as cost allows.
Power diode: voltage rating >1.3*Vout, reverse recovery time trr<1/(10*fr), Id>2*Iout

Power inductor calculation: L1= (Vout-Vin)*Vin/(Vout*0.2*Iout*fs); note saturation current ≥1.2*Iout

Input/output capacitors: high-frequency low-ESR electrolytic

Applications: industrial power, chargers, solar PV supply, DC generator supply, etc.

Typical application circuit:

Boost (Step-Up) Circuit Design — figure 4 — FIG.04 · CLICK TO ENLARGE